Iec tr 62258 3 2005

4.4.4.1 Pick-up tools and collets A wafer extraction tool should be used to assist in guiding the wafer out of a cassette in order to avoid scratching or damaging the wafer.. 5 Process h

General

Contact with the exposed active surface of die products should be avoided When contact is absolutely necessary, only properly designed tools and materials should be used

The working environment, including tools, materials and containers for handling and transport of die products should provide for ESD protection (refer to IEC 61340-5-1 and IEC 61340-5-

It should also be realised that die products are sensitive to certain chemicals.

Working environmental controls

For optimal performance of semiconductor technologies, it is essential to maintain specific working environmental conditions The recommended temperature range is between 17 °C and 28 °C, with humidity levels ideally at 40% ± 10% Additionally, the particle count should meet ISO 14644-1, Class 8 standards or better It is important to note that this environment should not be used for storing semiconductor die, and a thorough characterization of the specific technology is necessary to identify any unique environmental requirements.

General handling precautions

The selection of appropriate tools is critical to successful handling of bare die and wafers

Specialized tools are essential for the proper handling of dies and wafers If any tooling or equipment is identified as damaging to die products, its use must be halted immediately.

Die products should never be allowed to come into contact with each other, or to be stacked on top of each other without the use of suitable separators

To prevent damage, die products must not be placed with the active side against any hard surface Additionally, contact with soft surfaces containing hard particles, like silicon debris, can also harm the die surface.

When handling wafers it is recommended that physical contact should be made only with the outer periphery and/or the back side of the wafer.

Cleanroom good practice

Bare die or wafer containers must be opened exclusively in a controlled environment, referred to as a cleanroom This requirement is crucial for any procedure that exposes the die or wafer surface to the surrounding environment, including quality inspections, die sorting, and the assembly of products that incorporate bare die.

Personnel working in these areas need to be adequately trained to ensure that die products are not physically damaged nor contaminated when handled in the cleanroom

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To minimize ESD damage, it is essential to utilize grounded workstations, conductive wrist and shoe straps, and conductive material totes Additionally, incorporating staticide chemicals, conductive floor waxes, tiles, mats, ionizers, conductive packing foams, and shielded bags can enhance the effectiveness of environmental controls.

To ensure optimal conditions, bare die or wafers must always be kept in a clean environment When transporting wafers between cleanrooms, it is essential to use an appropriate wafer carrier, keeping the container closed throughout the process Additionally, the container should be thoroughly cleaned on the outside before re-entering the cleanroom.

To prevent contamination, it is advised to avoid handling die or wafers manually, as bare hands can transfer skin oils, flakes, and other contaminants Even with gloves, there is a risk of contamination from plasticizers However, wafers can be safely handled with gloved hands if they are held by the edges, ensuring that the active surface remains untouched.

To ensure the integrity of die products, all surfaces in contact with them must be kept clean and, whenever possible, made of non-metallic materials Hard materials can lead to scratches or chipping on the die products It is crucial to adhere to these guidelines consistently, as contamination of one die or wafer can result in the transfer of contaminants to other surfaces, process equipment, and additional wafers.

To prevent contamination during product handling, it is essential to keep working surfaces free from non-clean items like equipment covers, internal parts, and personal belongings Simply wiping a surface may not effectively eliminate oils and residues, highlighting the need for thorough cleaning practices.

4.4.2.1 Hats, hoods, nets, masks and shoes

Head and facial hair should be completely enclosed at all times using appropriate hoods or nets to avoid contamination from skin particles or hair

Wearing masks at all times in the production area with exposed wafers or die is essential to prevent contamination from spittle Masks should adequately cover both the mouth and nose, and they should be replaced daily or more frequently if they become contaminated.

In cleanroom environments, it is essential to wear specialized ESD-safe shoes, which must remain within the cleanroom or designated changing areas, only being taken outside for cleaning or repairs Alternatively, disposable overshoes can be utilized, but they should be discarded immediately after use in appropriate waste containers While some overshoes can be washed and reused, they must be cleaned before any subsequent use.

Special smocks and gowns should be worn within the cleanroom, to cover normal clothing

They should be selected according to the cleanroom classification and should be made of material that is both anti-static and lint-free

Gloves act as a crucial barrier against the release of skin flakes, oils, and other contaminants from hands For general use, disposable vinyl gloves that meet cleanroom standards are highly suitable.

When handling die products, avoid using cotton gloves or any gloves that shed lint or powder, even if worn under vinyl gloves Instead, opt for polyester or nylon gloves, which are suitable for use beneath vinyl gloves.

Rubber gloves packed with powder should not to be used

In a cleanroom environment, it is essential to replace gloves each time you enter, or more frequently if they become contaminated, such as from ink or contact with the face Additionally, any gloves that show signs of rips or tears must be replaced immediately to maintain cleanliness and safety.

When donning personal protective equipment, it is essential to put on gloves last, following the application of other items Ensure that gloves are worn over the cuffs of sleeves and are secured at the wrists at all times.

Gloved hands should avoid contact with the face, hair, or any potential sources of contamination, as this can lead to the transfer of contaminants to other items, including die products, process equipment, and handling equipment.

Finger cots serve as a convenient alternative to gloves, particularly in tasks like wafer quality control inspection, despite offering less protection against contamination To minimize the risk of inadvertent contamination, it is advisable to wear finger cots on all fingers Additionally, finger cots should be stored and utilized exclusively within the cleanroom area, rather than in the gowning area.

Finger cots should not be re-used and should be replaced if torn or damaged Fresh finger cots should be used after re-entering the cleanroom

Food and drink should not be taken into the cleanroom

Hands should be washed before gowning and entering the work area, especially after handling foods

Cosmetics and excessive creams or lotions should be avoided in cleanrooms, as their chemical components can potentially damage or contaminate die products.

Wafer sawing

Wafer sawing is a crucial step in preparing die products from unsawn wafers, typically achieved by cutting the wafer with a high-speed, high-precision diamond-tipped saw blade The wafer is secured to a pressure-sensitive adhesive (PSA) tape attached to a film frame, which is available in various materials and sizes to meet different equipment requirements and accommodate various wafer sizes.

Silicon wafers are fragile, requiring careful handling during the sawing process to prevent damage to the individual dies Special attention must be paid to ensure that each die is separated effectively while maintaining their integrity.

– flow rate of rinse and cutting water,

– dual blade sawing to fully cut away process control modules/test structures in the saw lane, and

– back side and front side chipping

For bare die and flip-chip products, it is advisable to utilize a "bevel" cut to prevent edge chipping and cracks on the front, sides, and back This beveling process also reduces metal flakes from the die edge, which can occur when a nickel/diamond blade cuts through aluminum test grids Adhering to this recommendation is crucial, as any deviations can lead to defects that compromise the quality of the die.

Figure 1 provides a pictorial view of the bevelled edge for both wire-bonded and flip-chip processing

Figure 1 – Bevel cut for bare die and flip-chip products

To avoid edge chipping, it is advised against using a finger or any tool to check the saw cut under a mounted cut wafer, as this may lead to adjacent die shifting against one another.

Other wafer material, such as gallium arsenide (GaAs), composites such as silicon on sapphire (SoS) or bonded wafers, require special saw processes

Selecting the right film material for wafer mounting is crucial, as industry experience shows that using specific films can significantly reduce defects after wafer dicing It is advisable to consult with the film vendor to identify the optimal film for your application, considering factors such as higher modulus and increased tack levels.

UV films have all shown improved performance in reducing die chipping and fractures

Water plays a crucial role in the sawing process, serving as a lubricant, coolant, and slurry rinse To protect the dies from potential damage caused by contaminants, it is essential to use only ultra-pure water.

Ultra-pure water, typically generated through deionization, is highly resistive, leading to the accumulation of static charges during sawing To mitigate this static hazard, a small amount of pure carbon dioxide gas is often introduced into the water through bubbling However, it is crucial to control the CO₂ levels, as excessive amounts can render the water acidic and corrosive.

Water additives may be used to improve the cutting process Any additive used should be fully assessed to ensure die are not damaged by chemicals contained in the additive

Residue from the cutting process may remain on the surface of the wafer It is normal to rinse or wash the cut wafer using ultra-pure water

The process used to dry the wafer after washing should ensure that the surface is clean and dry.

Die sorting

Die products can be provided in wafer form, either pre-sawn on adhesive film or unsawn, necessitating sawing prior to use In both scenarios, individual die are extracted from the adhesive film utilized during the sawing process for integration into the final product.

When selecting equipment for wafer processing, it is crucial to ensure compatibility with the specific wafer type and technology Special attention should be given to particularly sensitive dies, such as unpassivated or extremely thin and fragile dies, as they are more susceptible to damage.

Die removed from the adhesive film may be placed into a die carrier for subsequent assembly

Die sorting is a crucial process that segregates electrically functional die from defective ones, as well as categorizing them into various grades The carrier systems used for individual die include chip trays, vacuum release trays, and tape-and-reel methods.

5.2.1 Guidelines for handling frames containing sawn wafers

After sawing, the wafer will be securely mounted on the film frame, which must be properly positioned on a holding fixture This fixture is essential for ensuring that the frame remains stable during indexing, loading, unloading, and die removal processes.

Best results are obtained under good vacuum conditions at the pick-up tool and beneath the wafer-film Manufacturers’ recommendations on vacuum pressures should be followed

To ensure proper engagement between the pick-up tool and the die, it is essential to minimize the contact force and start with a slow ascent rate The timing of the plunge-up needles and the pick-up tool must be coordinated so that the die stays in contact with the tool until it is fully separated from the film A rapid ascent can lead to premature separation of the die from the tool before it detaches from the membrane.

The commonly used adhesive-backed film for mounting wafers experiences a change in adhesive strength after being removed from the roll due to a silicone spray added as a release liner Over several weeks, this additive is released into the atmosphere, resulting in an increase in adhesion by a factor of five or more after sawing, which can complicate the die removal during sorting To mitigate this issue, it is advisable to conduct the die sorting process as soon as possible after sawing Alternatively, other adhesive-backed films, such as UV tape, are available that do not present this problem.

In the die sorting process, a needle or needle bed is typically used to detach die from the adhesive-backed film during sawing However, thin or fragile wafers are not suitable for needle offload For small die, a needle with a small radius tip and a smaller angle A is recommended to puncture the film, enabling the adhesive-backed film to peel off without damaging the die's back Conversely, for larger die, needles with a larger radius tip and a greater angle A should be employed; these needles should elevate the die without puncturing the film, ensuring that the film peels off cleanly without leaving adhesive residue on the die's back.

Die have various back side surface finishes, some of which are more susceptible to damage by a needle than others

The needle tip profile is crucial for preventing damage during the die sorting process, with the radius of the tip being a key feature.

Examples of marks caused by die eject needles on the back surface of a back-lapped die are shown in Table 1

Table 1 – Example die eject marks

Description Normal lighting Dark-field lighting Accept/reject Cause/remedy

No needle mark or film adhesive residue

Accept Correct die eject set-up – no visible needle mark or film adhesive residue

Excessive needle mark showing micro-cracks

Reject unless there is no evidence of microcracks

Heavy needle mark caused by too much ‘over-travel’ or wrong choice of needle Reduce over-travel or change needle

Excessive needle mark, scratches and micro-cracks

Reject Too much over- travel and incorrect machine set-up resulting in needle bounce Adjust machine set-up, die eject speed and needle over-travel

Excessive needle mark with scrape and residue

Reject Die eject not perpendicular to die surface caused by incorrect machine set-up or broken needle Check machine die eject/replace needle

Certain die types are unpassivated and need careful handling to protect the active surface from damage Using a standard vacuum pick-up tip can lead to scratches on this surface Instead, a soft rubber tip or a collet that securely grips the die's edge is recommended for safe handling.

MEMS and sensors often have delicate mechanical features at the center of their active surfaces, which can be easily damaged by standard pick-up tips To prevent this, it is advisable to use a collet that securely grips the edge of the die.

When dealing with MEMS and sensors that possess mechanical features extending through the die, it is crucial to avoid using a needle for normal die ejection, as this can potentially damage the mechanical components located on the underside of the die.

6 Die and wafer transport and storage media

Various shipping and storage media are available for transport or storage of die and wafers

Wafer cassettes may be used for transportation and storage within a single facility Wafer shipping carriers and containers may be used when transferring product between facilities

Shipping and storage boxes are essential for managing sawn wafers on frames, which consist of adhesive-backed film supported by a frame For transporting singulated die, options include chip trays, vacuum release trays, or reels of adhesive-backed carrier tape and pocketed tape.

To minimize exposure to work-area air, it is essential to store wafers and dies in appropriate closed containers or sealed bags for reels of die on tape.

To prevent contamination from airborne particles or moisture, containers of die or wafers must remain sealed outside the cleanroom Additionally, products transported by air should be securely packaged in hermetic bags or containers.

Die and wafer containers must be handled with care and should never be touched with ungloved hands, even outside the cleanroom This precaution is essential to prevent ionic contamination from being transferred to the product when the container is opened in the cleanroom.

Die and wafer storage containers and cassettes should be cleaned regularly, especially whenever visible contamination is present

Die and wafers should remain in their carriers at all times and should only be removed when they are in process

Wafer carriers and cassettes

At various points during their production, semiconductor wafers are transported between different equipment and facilities, such as:

– raw wafer processing and shipping;

– wafer processing including patterning, metallization and passivation;

– back-end processing including test, thinning and bumping;

– finished wafer shipping and handling

Any of these stages can take place in facilities remote from each other It is also common to have some stages sub-contracted out to another company

Differentiating between transportation carriers and shipping carriers is crucial, as using a carrier meant for internal wafer transport to ship wafers to another facility can lead to breakages While these carriers are designed to securely hold wafers for hand or robotic movement within a facility, they are not suitable for packaging and shipping through a transport company.

When selecting a shipping or process carrier, it is crucial to prioritize care to prevent damage to the edges of unsawn wafers Such damage can lead to the formation of micro-cracks, which may later propagate during processes like mounting on film, back-grinding, or sawing This can ultimately result in the wafer breaking or shattering during handling.

Wafer cassettes should be handled from the ends, touching only the exterior surfaces Avoid picking up a cassette from the top

When transferring wafers to a different carrier, it is essential to use slide transfer (cassette to cassette) whenever possible, ensuring that wafers slide gently Avoid dump transferring, as it can lead to damage or contamination of the wafers.

In-process carriers and transport systems

A wafer cassette is the primary form of container used in transporting and storing wafers

To optimize wafer handling, it is advisable to manage cassettes as a single unit instead of dealing with individual wafers Various carriers are specifically designed for both sawn and unsawn wafers, facilitating their movement within the processing area and providing temporary storage solutions.

They are not designed for shipping wafers

Sawn mounted wafers are offered in two versions: on a film frame or a grip ring It's important to recognize the wide range of film frame sizes and types available, making the careful selection of the appropriate carrier essential.

Packing for shipment of unsawn wafers

Wafer tubs or jars are essential for transporting unsawn silicon wafers, and it is crucial to adhere to the manufacturer's packing instructions during loading and unloading to prevent any damage to the wafers.

The typical structure of a wafer shipping jar consists of a lid and base, featuring a lining made of static dissipative material to securely hold the wafers, which are interleaved with separators Each jar usually contains fewer than 50 wafers, and it is advisable to include wafers from only a single lot per jar After securing the lid, a label with essential product identification and traceability information should be affixed to the top The jar is then placed in an ESD shield shipping bag, which also requires an external label To prevent wafer breakage, it is crucial to overfill the jar, as this creates light compression on the wafers when the lid is snapped on, minimizing movement and potential damage.

4 Spun-bonded lint-free disk

6 Wafer container with static dissipative foam

8 ESD shield bag with ID and ESD labels

Wafers should only be removed from shipping jars in a cleanroom environment while adhering to proper ESD procedures to maintain product quality The use of air ionizers is recommended during the handling and processing of wafers and wafer cassettes Care must be taken when removing wafers, as contact with tools like pick-up wands or tweezers can cause micro-scratches on the active surface Manual handling of wafers should be avoided to prevent damage.

Wafer jars are not ideal for long-term storage of wafer products due to the degradation of the commonly used foam liner, which releases harmful fluorine when exposed to light However, there are special closed-cell foams filled with nitrogen that do not degrade or emit gases, making them suitable for extended storage For specific information on the type of foam used, it is advisable to consult suppliers.

Packing for shipment of sawn wafers

When sawing a wafer, it is attached to an adhesive film secured by a film frame or grip ring Transferring wafers from the frame to grip rings allows for further stretching of the film, facilitating die separation and improving the offload process.

Shipping wafers with this method has a limited storage duration before the dies must be offloaded, as the adhesive used in this film tends to lose strength over time.

After the wafer is mounted, the adhesive strength starts to increase, which can aid the sawing process but complicates the die offload process The longer the die remain on the film, the more challenging they are to remove Therefore, it is crucial to remove the die promptly after sawing for optimal efficiency.

Other film types are available which have different adhesive properties, for example UV film

After sawing, specific films utilize light of a certain wavelength and/or heat to weaken the adhesive, facilitating the easier removal of the die from the film.

Whichever film system is used, sawn wafer on film should not be used for long-term storage of wafers

A 'film frame' refers to a specialized frame that holds an adhesive film and wafer for die processing and transportation These frames are made from various materials and are available in different sizes to meet the requirements of diverse equipment and wafer dimensions Typically, film frames feature two registration notches on one edge to enhance handling efficiency with automatic machinery.

Film frames are securely packaged in shipping frames, with a label affixed to the lid This assembly is then enclosed in an ESD shield bag along with a desiccant, and a final label is attached to the exterior.

Figure 4 provides a pictorial view of this structure

The quality of wafers is significantly influenced by their storage and handling environment To maintain optimal conditions, it is advisable to use die shipped in this format promptly, as the tack level of the film may increase over time For specific guidance on recommended storage durations, consulting the supplier or manufacturer is essential.

A 'grip ring' refers to a two-part circular frame designed for mounting an adhesive film and wafer, essential for die processing and transportation These grip rings are produced from various materials and are available in multiple sizes to meet specific equipment requirements and accommodate different wafer dimensions.

Grip rings are engineered without registration notches to enhance handling by automatic equipment They are stored in a shipping container with a label affixed to the lid, then placed in an ESD shield bag along with a desiccant, and finally, a label is attached to the exterior For a visual representation of this setup, refer to Figure 5.

The ring or frame should be well positioned on a holding fixture The fixture should securely hold the ring during any indexing, loading, unloading or die removal

To ensure proper engagement between the pick-up tool and the die, it is essential to minimize the contact force The ascent rate should start off slowly, allowing for precise timing of the plunge-up needles and the pick-up tool This coordination is crucial to maintain contact between the die and the pick-up tool until the die is fully separated from the membrane.

Rapid ascent can lead to the separation of large dies from the tool before they detach from the membrane It is essential to use at least three needles for film penetration and die presentation, although only one needle may be sufficient for very small dies To neutralize electrostatic charges on the die and equipment during removal, a continuous flow of ionized air should be directed onto the wafer's surface.

Packing for shipment of single wafers

These carriers are for use with sawn or unsawn wafers mounted on film and are designed for shipping single wafers

A carrier specially designed for shipping single wafers is preferred

This system supports various versions for wafers mounted on either film frames or grip rings, ensuring compatibility with a wide range of film frame sizes and types.

Another technique involves placing the film frame or ring with a rigid support into a vacuum– sealed, ESD shield bag This shipping method is suitable only for sawn wafers

A custom separating disk is placed over the face of the wafer to protect the surface of the die

A low-lint laboratory grade filter paper disk is positioned over the separating disk to fully cover the interior width of the frame Next, a card or thin board disk, smaller in diameter than the frame's inside diameter and approximately half the frame's thickness, is placed on top of the filter paper Additionally, a second card or thin board disc is positioned on the underside of the film frame, completing the assembly before careful placement.

ESD shield bag and sealed using a vacuum sealer

The sealed bag is placed in an anti-static cardboard box for shipping, which may feature a cushioned interior for a single wafer or accommodate multiple wafers stacked together, with each wafer individually vacuum-packed.

In the case of a sawn wafer on film mounted in grip rings, a similar packing method may also be used.

Packing for shipment of die using trays

Die products may be presented to placement machines in a variety of ways including waffle packs, vacuum release trays, die on tape and sawn wafer formats

The particular packing form selected may be based on volume and throughput considerations

Whereas both waffle pack and tape feeding require die-sort/pick-and-place processes upstream from chip attach, tape feed is better suited to higher volumes

Waffle packs, also known as chip trays, are essential for the handling and shipping of die products, including bare die, CSP, opto-electronics, and other microelectronic devices These trays are constructed from various materials tailored for specific applications, with a focus on using ESD-safe materials for die products Each pack is designed for a narrow range of die sizes, featuring compartments that securely hold the die in place Typically, waffle packs are available in sizes of 50 mm² or 100 mm².

Each pack or tray features a matrix of cavities designed to hold dies, with various types available that differ in cavity dimensions such as width, length, and depth Key handling challenges involve managing the aspect ratio and ensuring the die size is appropriate for the cavity dimensions of the selected pack or tray.

To minimize die movement during handling and prevent potential damage, it is essential to shorten the search time for die fiducials and enable the use of optimal pick tools.

Ideally, the cavity size should be no more than 10 % larger than the die size in each axis

After placing a lint-free sheet over the die, a lid and clips are secured The waffle packs are then inserted into an ESD shield bag along with a desiccant, and a final label is affixed to the exterior of the bag.

Waffle packs may be in a single (see Figure 6) or stacked (see Figure 7) configuration

Different clips are available for these configurations

After the clips, lid, and lint-free sheet are removed, the die can be effortlessly extracted with a vacuum pick-up tool It is essential to ensure that the tray is properly positioned on a holding fixture that securely supports it during indexing, loading, unloading, or die removal.

6.6.2 Vacuum-release (VR) trays for die products

VR trays utilize a unique gel membrane over a mesh material, distinguishing them from traditional waffle packs This innovative design securely holds dies on the membrane's surface, ensuring safe handling and shipping.

Die are dispensed on demand by creating a vacuum beneath the membrane through an opening in the tray's bottom Once released, the die can be easily retrieved with standard pick-up tools The VR tray design allows for the loading of various die sizes simultaneously, as it does not feature any pockets.

The reusable trays are ideal for handling small or fragile die products, particularly in high-speed pick-and-place operations Featuring a proprietary gel membrane, these trays securely hold the die in place, safeguarding the edges and top surface from damage without requiring a lid insert The cover's depth provides sufficient clearance between the lid and the die, ensuring proper orientation once loaded, which minimizes the need for corrections by the pick-and-place equipment.

Die are typically arranged in a matrix format, utilizing rows and columns with X and Y coordinates originating from the reference corner of the tray Adequate spacing is maintained between the rows and columns to facilitate the removal of individual die without affecting neighboring ones.

The lid's depth must create a gap between its interior and the die's top After sorting the dies into trays, a product label and clips are added to the lid The trays are subsequently enclosed in an ESD shield bag with a desiccant, and a final label is affixed to the bag's exterior Figure 8 illustrates this setup.

6.6.2.1 Guidelines for handling vacuum-release trays

To ensure optimal performance, the tray must be securely placed on a holding fixture that provides vacuum support to its underside Additionally, the fixture should incorporate a rubber gasket or O-ring to effectively prevent any leakage within the system.

Best results are obtained under good vacuum conditions both at the pick-up tool and at the tray Manufacturers’ recommendations on vacuum pressures should be followed

NOTE The gel membrane may appear to be in a release mode even under relatively low vacuum conditions

Therefore, one should not rely on the appearance of the gel membrane as evidence for adequate vacuum

Heated collets or pick-up tools should be avoided for die removal from the tray due to the membrane material's properties If the use of heated tools is necessary, the initial pick-up must adhere to the specified guidelines, with the die then moved to an intermediate stage for the final pick and bond process.

Membranes are delicate and require careful handling to prevent tears, which can lead to vacuum leakage at the tray and hinder die removal In cases where a tear affects die removal, applying a small piece of tape over the damaged area may be necessary to resolve the issue.

6.6.3 Recommendations for die orientation in trays

Orientation of die in trays is an issue with many facets The die user needs to take into account the die assembly methods, applicable standards and cost

Die should be consistently placed in the tray using the same orientation Where necessary, the die orientation should be specified

Each tray must exclusively hold die from a single chip or bump lot Partially filled trays are acceptable, provided that the labels and documentation accurately reflect the correct quantity.

For flip-chip products, die are loaded into the vacuum release tray with the bumps facing up, or away from the gel

During transportation, the corners of the dies are prone to damage due to their unrestricted movement within the cavity This issue can be addressed by utilizing chip tray cavities designed with half-moon corners, as illustrated in Figure 9.

Figure 9 – Corner relief in the cavity of a chip tray

Packing for shipment of die using tape-and-reel

Tape-and-reel packing systems are primarily intended for high volume and automated handling

The IEC 60286-3 standard outlines the guidelines for selecting and designing tape-and-reel packing systems specifically for surface mount components, including die products.

Details about embossed, adhesive backed and punched tape are fully defined in IEC 60286-3

6.7.1 Embossed tape with cover tape

Embossed tape, also known as pocketed tape, is commonly used for delivering components designed for assembly on high-speed automation equipment This tape features individual pre-sized pockets or tub-like cavities that securely hold each component, with each pocket sealed by a cover tape For convenient handling, the tape is wound onto a reel.

Embossed tape is specifically designed for the shipping and handling of die products, utilizing a unique embossing technique to create pockets with exact dimensions and a flat bottom to prevent damage or scratches Additionally, corner relief features are included to protect the edges of the die This type of tape is essential for transporting both bare and bumped die from suppliers to customers, allowing for flexible loading options with the active side facing either up or down as needed.

The structure features a base tape made of conductive material with customized pockets for the specified die size A static dissipative cover tape is applied along the tape's length to secure and protect the die during shipping and assembly Finally, a product ID label is affixed to the reel, which is then placed in an ESD shield bag that includes both a product ID and ESD label.

6.7.2 Punched tape with top and bottom cover tape

Punched tape features a conductive carrier with cavities designed to fit specific device dimensions, incorporating industry-standard sprocket holes It is equipped with static dissipative cover tapes on both the top and bottom Unlike paper-based alternatives, this type of tape is not suitable for die products.

The thickness of the carrier tape is directly proportional to the thickness of the device, thus providing protection to the device while preventing tilting or inversion of the device

Clear cover tapes on both the top and bottom of the carrier tape enable visual inspection of the device from both sides Additionally, punched tapes facilitate the taping and reeling of bare die and wafer-level packages with the active side positioned either on the top or bottom, thereby removing the need for flipping during tape-and-reel or pick-and-place operations.

Corner reliefs may be included in the cut-outs to ensure there is no damage to the corners of the devices and to ensure a clean pick-and-place operation

6.7.3 Adhesive-backed punched carrier tape (without cover tape)

Adhesive-backed punched carrier tape is a punched conductive plastic carrier containing pressure-sensitive adhesive (PSA) tape affixed to the bottom side Die are retained by the

PSA tape maintains a fixed orientation until it is picked, eliminating the need for a cover tape and preventing component displacement during the peel-back process This design ensures that components remain accessible for inspection, testing, marking, and other automated processing The adhesive-backed tape is specifically designed for packing singulated bare die, facilitating high-speed automated chip-on-board (COB) and flip-chip assembly.

This system excels in managing small or delicate die and is ideal for high-speed pick-and-place operations It features oversized compartments that allow a single tape size to fit various die sizes The die are securely taped in consistent positions, centered at a reference point aligned with the sprocket drive holes This design enables 'blind picking' of each die from the tape, eliminating the necessity for machine vision.

When applying cover tape to embossed or punched carrier tape, it is crucial to ensure a smooth peel during the de-taping process Extreme care is necessary when de-taping bare die to prevent the die from bouncing out of the carrier.

6.7.5 Orientation of die in tape-and-reel

The orientation of die in tape-and-reel presents multiple challenges that die users must consider, including assembly methods, relevant standards, and cost implications However, as tape-and-reel systems are optimized for high-speed assembly lines, any adjustments made by the pick machine to correct orientation can negatively impact both the speed and accuracy of component placement.

The orientation of the die must be mutually agreed upon by both the customer and the supplier It is essential that the die is consistently positioned in the tape with the same orientation, as any die that is misaligned may be deemed defective Additionally, any alterations to the die orientation for an existing product should be treated as a product redesign, necessitating adequate notification.

6.7.6 Tape-and-reel packing structure

The inner shipping structure for shipping the product in a tape and reel is represented in

After the dies are inserted into the tape and spooled onto the reel, a product label is affixed for identification The spooled tape is then placed in a vacuum bag with a desiccant and sealed Finally, an additional label containing the same information is attached to the exterior of the bag.

Figure 10 – Tape-and-reel packing structure

Secondary packing for shipment

The final shipping structure is designed to protect devices from mechanical, electrical, and environmental hazards during transit while adhering to environmental standards Each product is sealed in a specialized static protective vacuum bag and placed in an inner shipping box lined with shock-absorbent material A product identification label is affixed to this inner box, which is then placed inside an outer shipping box, also lined with shock-absorbent material, and labeled accordingly This multi-layered packaging ensures optimal protection throughout the shipping process.

Figure 11 – Packaging material for shipment

Die and wafer storage

Die and wafers can be briefly stored in open containers during operation if exposed only to clean air, ideally from uninterrupted laminar air flow However, at all other times, they must be kept in clean containers within a controlled environment, known as short-term storage Opening a container allows outside contaminants to enter, potentially compromising the die products and the container itself Therefore, it is crucial to store containers in a clean environment and to open them gently in filtered air Unsealed containers should also be maintained in a controlled environment to prevent contamination.

Doors on cabinets should be kept closed at all times when not in use.

Short-term storage environment and conditions

To ensure optimal preservation of devices when not in use, it is essential to store them in an inert environment, such as dry air or nitrogen, preferably within the manufacturer's original container or a suitable alternative for bare die or wafers Recommended storage conditions for most die devices include an atmosphere composed of 99% nitrogen or dry air, a temperature range of 17 °C to 28 °C, and a relative humidity (RH) between a minimum of 7% and a maximum of 30%.

(A minimum of 7 % RH is desirable to avoid electrostatic damage) d) Particle count: ISO 14644-1, Class 6

In short-term storage settings, maintaining appropriate humidity levels is typically achieved by continuously introducing filtered dry air or dry nitrogen It is crucial to monitor and manage any static charge accumulation that may arise from the dry environment to prevent potential damage to dies or wafers.

Storage time limitations

Maximum recommended storage times are governed by several different modes of deterioration, for example:

– wire bondability is limited by both build-up of oxide and deposit of organic contaminants;

– solderability of flip-chip with solder bumps may be limited by build-up of oxide;

– die stored on wafer film frames may be subject to problems of removal from the adhesive which tends to increase in strength over time;

– retrieval of die stored in embossed or punched tape may be subject to problems in removing the cover tape due to increasing strength of adhesive;

– die with organic passivation (polyimide or BCB) tend to absorb moisture which will subsequently outgas during high-temperature processing;

– all bare die and wafers should be protected from contaminants that could lead to corrosion and semiconductor junction failures during use

Ambient conditions such as temperature, humidity, oxygen levels, and purity significantly affect the storage of dies in carrier tape or wafers in cassettes It is essential to treat these dies as bare dies or wafers, as the tapes and cassettes do not provide adequate protection against moisture or other contaminants.

Sawn wafer on wafer frame or ring

Die should not be stored on wafer frames with solid sticky tape membranes, as the adhesion of commonly used tapes can increase significantly—by five times or more—within just two weeks of atmospheric exposure This heightened adhesion can lead to challenges in die retrieval from wafers, potentially causing die breakage, edge chipping, and latent defects due to excessive stress.

Die products in the production area

Exposed dies or wafers must not remain in the production area atmosphere for over 8 hours When not in use during production or at the end of a shift, they should be promptly transferred to an appropriate storage container.

Die in tape-and-reel

Die in tape-and-reel should ideally be utilized within 12 months when kept in a controlled environment After this period, the adhesive on the cover tape may weaken, leading to increased adhesion and making the cover tape challenging to remove.

Dry-packed die products

Dry-packing has a finite effective life due to the deterioration of the desiccant and moisture penetration through the packing material

General

Traceability is crucial for die products, as most dies or wafers lack unique markings for product type and lot number In contrast, MPDs and CSPs are typically marked like packaged products, eliminating the need for special traceability measures.

Wafer traceability

Wafers typically feature lot markings that are either scratched or etched on their edges or back sides These markings serve to uniquely identify each wafer or indicate its association with a specific batch of wafers processed together.

If the wafer is to be thinned before use, then any marks on the back of the wafer will be lost

Care should be taken to ensure that traceability of the wafer is not compromised if these marks are lost

Normally, traceability is only required to the process lot which may comprise anywhere from

20 to 50 wafers However, some applications require that individual wafers are traceable within the lot.

Die products traceability

It is essential to retain all information from labels on the primary packaging with the batch of dies until the assembly process is finalized or until the dies are transferred to different primary packaging containers.

Die from different lots should be kept segregated Die from different lots should not be placed in the same chip tray

A reel of taped die may include products from various wafers within the same lot or from different lots, necessitating the identification of these lots or wafers for traceability To achieve this, blank pockets can be inserted between die from different wafers or lots It is essential to document the order of wafer loading on the tape alongside the wafer traceability information for all die in the reel During the assembly process, automatic pick-and-place machines are programmed to halt if they detect two or more empty pockets, allowing operators to recognize a lot change and update the relevant traceability information.

Certain programmable devices may store lot traceability information electronically within their on-chip memory It is crucial that any subsequent processing preserves this electronic lot traceability data and prevents its erasure.

Wafer and die back side marking

Die or wafers may be marked on the back to aid identification and traceability, especially for flip-chip products

Commercial wafer marking utilizes lasers, which must be chosen and adjusted meticulously to achieve clear markings while preventing damage to the wafer's backside It is crucial that the laser mark does not penetrate excessively into the material or harm diffusion zones due to localized heating.

Die with laser marking may need special die attach methods or conditions

Back side marking can be achieved with appropriate permanent ink that withstands processes like wafer sawing and washing It is essential to conduct tests to verify the durability of the marking and to confirm that the ink does not harm the wafer or die material Typically, dies marked with ink are utilized for flip-chip attachment.

A complete wafer may be marked on the front surface around the edge of the wafer All active areas of the wafer should be avoided

9 Guidelines for long-term storage (die banking) of bare die and wafers

General

Long-term storage of dies or wafers requires careful consideration to ensure their usability after several years It is crucial to focus on the storage media and the surrounding environment to maintain the integrity of the dies Additionally, important data, such as wafer maps, must remain accessible for future processing of the product.

These guidelines do not imply any warranty of product or guarantee of operation beyond the storage time given by the manufacturer.

Preparing for storage

Only products that can reliably demonstrate correct functionality should be stored For wafers, they must be inked or accompanied by a human-readable wafer map Relying on wafer maps stored on electronic media is not advisable, as they may become illegible by the end of the storage period.

The best conditions for accelerated testing of storage reliability are through temperature cycling or humidity cycling or a combination of the two

Damage to die products during long-term storage

Defects caused by mechanical damage may affect different regions of the die or wafer and should be considered when designing long-term storage schemes

9.3.1 Long-term storage failure mechanisms

Failure mechanisms that may occur during long-term storage include:

– outgassing of packing materials causing ionic contamination;

– humidity infiltration of packing material causing metal corrosion;

– interactions between incompatible packing and/or IC materials causing hazardous reactions;

– temperature cycling causing metal fatigue, solder creep or glassivation crazing;

– improper handling causing cracking, scratches or contamination to die surfaces;

– non-specific electrical or radiation events in the atmosphere causing gate oxide and metallization failures;

– piezo-electric effect – changing electrical parameters through in-built stress,

– photovoltaic effect – changing electrical parameters through imposed charge,

– electrical overstress caused by ESD or other sources of radiation

To ensure proper mechanical protection for dies and wafers, it is crucial to handle their initial placement in storage containers and their removal with care, as damage can easily happen during the loading and unloading processes.

To ensure product safety during storage, it is crucial to protect against movement and vibration Proper die or wafer orientation is essential, particularly for MEMS or sensor products, to reduce the risk of damage from shock Additionally, containers and shelving should incorporate anti-vibration or anti-resonance features, while packing materials must be designed to provide adequate protection against shock and vibration.

Die and wafers should not be inspected unless required under a specific sample programme in order to minimize the amount of handling to which the die or wafers are subjected

Material in contact with the wafer or die surface should ensure that there is minimal abrasion and adhesion of foreign matter to surfaces.

Long-term storage environment

Long-term storage conditions are more rigorous than those for short-term storage, as the storage environment plays a crucial role in ensuring success The recommended methods may not be appropriate for shipping, particularly by air Key requirements include an atmosphere composed of 99% nitrogen or inert gas, a temperature range of 17 °C to 25 °C, humidity levels with a minimum of 7% and a maximum of 25%, and pressure maintained slightly above ambient atmospheric levels.

The gas pressure should be sufficiently high to prevent the ingress of external contaminants

To control the relative humidity, it is normal for die and wafer storage environments to use high-purity nitrogen, for example, derived from a liquid source

To prevent the build-up of electrostatic fields, relative humidity must remain above 7%, while it should not exceed 25% to avoid condensation and moisture ingress After opening a storage cabinet, it is essential to quickly restore the relative humidity, often achieved by installing a timed purge regulator.

Any temperature or humidity excursions outside these limits should be recorded and logged

To ensure product integrity, it is essential to address temperature and humidity conditions that exceed acceptable limits with appropriate corrective measures While minor excursions may not cause permanent damage to stored products, it is crucial to consider these out-of-limit conditions when retrieving the product for use.

Recommended inert atmosphere purity

Inert gas supply for the storage environment should satisfy the following:

– less than 0,5 % oxygen and argon,

Chemical contamination

To ensure the integrity of semiconductor devices, it is crucial to protect dies and wafers from ionic contamination and exposure to other chemicals This is important due to the mobility of contaminants within semiconductor materials, which can lead to unwanted intermetallic growths.

Protecting contact areas, active regions, and backside contacts is crucial, especially for wafers utilizing III-V materials, which require special attention due to their sensitivity.

Before placing bare die or wafers in a suitable container for long-term storage, it is essential to remove any degradable packing materials used for shipping This includes items that may cause chemical or particulate contamination due to long-term degradation, such as paper, cardboard, foam, or pink film Additionally, any ESD-coated materials should also be removed, as the coating can outgas during storage.

Vacuum packing is frequently utilized for shipping bare die and wafers, but it is not ideal for long-term storage This is because a vacuum can allow contaminants to penetrate the packing materials, leading to degradation over time Furthermore, the inclusion of desiccants may introduce minor particles into the packaging.

Foam is generally not suitable for use inside vacuum packs, as it can release absorbed contaminants when compressed However, nitrogen-filled, closed-cell foam is an exception and can be safely utilized.

9.6.2 Positive pressure systems for packing

Packing methods that use positive pressure are inherently better than vacuum-sealed bags

However, this requires good inlet filtering and is commonly implemented by initial vacuum followed by back-fill with nitrogen to help keep major contaminants out

9.6.3 Use of bio-degradable material

Certain packing materials, like the foam used in wafer jars or tubs, are intentionally biodegradable However, it is important to avoid using packing materials that are prone to deterioration, as the release of chemicals during this process can lead to product contamination.

– chlorine from cardboard and paper;

Certain foams, such as closed-cell foams filled with nitrogen, are engineered for durability and are not biodegradable When opting for a carbon-filled version of this foam, it is crucial to verify that the carbon is securely integrated into the material to prevent the release of particles during compression or disturbance.

Tiêu đề	Semiconductor Die Products – Part 3: Recommendations for Good Practice in Handling, Packing and Storage
Chuyên ngành	Electrotechnology
Thể loại	Technical Report
Năm xuất bản	2005
Thành phố	Geneva

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Số trang	50
Dung lượng	2,47 MB