Iec 60749 20 1 2009

3.3 mass reflow reflow of a number of components with simultaneous attachment by an infrared IR, convection/IR, convection, or vapour phase reflow VPR process allowable time period for

Assembly processes

Mass reflow

This standard applies to mass solder reflow assembly by convection, convection/IR, infrared

The article discusses the limitations of infrared (IR) and vapor phase (VPR) processes, specifically noting that these methods do not apply to mass solder reflow processes that involve immersing component bodies in molten solder, such as wave soldering for bottom-mounted components It emphasizes that such processes are prohibited for many surface-mount devices (SMDs) and are not included in the component qualification standards referenced in this document.

Localized heating

This standard also applies to moisture sensitive SMDs that are removed or attached singly by local ambient heating, i.e., ‘‘hot air rework.’’ See Annex B.

Socketed components

This standard is not applicable to socketed SMDs that are not exposed to solder reflow temperatures, as these components are not at risk and do not necessitate moisture precautionary handling.

Point-to-point soldering

This standard is not applicable to surface mount devices (SMDs) where only the leads are heated for solder reflow, such as in hand-soldering, hot bar attachment of gull wing leads, and wave soldering for through-hole components.

The heat absorbed by the SMD body during these operations is generally significantly lower compared to mass surface mount reflow or hot air rework, eliminating the need for moisture precautionary measures.

Reliability

The methods outlined in this specification guarantee sufficient SMD reliability during and after PCB assembly operations, as SMDs are assessed and verified according to IEC 60749-20 and/or IEC 60749-30, along with environmental reliability testing.

This specification does not address or ensure solder joint reliability of attached components

LICENSED TO MECON Limited - RANCHI/BANGALORE FOR INTERNAL USE AT THIS LOCATION ONLY, SUPPLIED BY BOOK SUPPLY BUREAU.

Requirements

Dry packing requirements for different moisture sensitivity levels are outlined in Table 1, based on IEC 60749-20 and IEC 60749-30 standards, along with reliability testing All materials utilized in dry packing must meet the applicable national packaging material standards for ESD-sensitive items.

Level Dry before bag MBB Desiccant MSID a label Caution label

Not required if classified at

220 °C to 225 °C A1 or B1 Optional Optional Optional Not required

Required b if classified at other than 220 °C to 225 °C A2 or B2 Optional Required Required Required Required

B2a-B5a Required Required Required Required Required

A Moisture-sensitive identification label (MSID) is optional, while a "Caution" label is not necessary if the level and reflow temperature are clearly stated in human-readable form on the barcode label of the lowest level shipping container.

Drying of SMDs and carrier materials before being sealed in MBBs

Drying requirements - level A2

Packing of the SMDs classified as Level A2 into MBBs shall be carried out within one week under the environmental condition below 30 °C/60 % RH after molding, burn-in, or bake

MET is not specified for Level A2 SMDs

MBBs can be briefly opened for under one hour and then re-closed if the HIC shows humidity levels below 30% RH, and the desiccant is replaced with a fresh one Upon the next opening of the MBB, it is essential that the HIC continues to indicate humidity below this threshold.

30 % RH, the duration time of the previous MBB’s opening may be disregarded Thus, if the

HIC indicates below 30 % RH when MBB is opened, the floor life is not dependent on the duration time of MBBs opening, and is 168 h at 30 °C/70 % RH.

Drying requirements - levels B2a to B5a

SMDs categorized from Levels B2a to B5a must be dried before sealing in MBBs, as outlined in Clause 6 The interval between drying and sealing should not exceed the MET, minus the time required for distributors to open and repack the parts If the supplier's actual MET exceeds the standard 24 hours, the actual time should be applied Additionally, if distributors typically repack MBBs with active desiccant, this time does not need to be deducted.

Drying requirements - carrier materials

The choice of materials for carriers like trays, tubes, and reels can influence moisture levels in the MBB To mitigate this effect and ensure the shelf life of SMDs, it is essential to either bake the materials or add extra desiccant as needed.

Drying requirements - other

Suppliers can leverage the drying effects of standard in-line processes, including post-mould cure, marking cure, and burn-in, to minimize bake time It is advisable to conduct an equivalency evaluation to confirm that high-temperature processing keeps moisture weight gain within acceptable limits The total weight gain of the SMD when sealed in the MBB should not surpass the moisture gain of the SMD when it starts dry and is subsequently exposed.

30 °C/60 % RH for MET h (less the time for distributors).

Excess time between bake and bag

If the allowable time between bake and bag is exceeded, the SMDs shall be redried in accordance with Clause 6.

Dry pack

Description

Dry pack consists of desiccant material and a humidity indicator card (HIC) sealed with the

SMDs and their carriers inside a moisture barrier bag (MBB) A representative dry pack configuration is shown in Figure 1

Figure 1 – Typical dry pack configuration for moisture-sensitive

Materials

The moisture barrier bag shall meet relevant national standard requirements for flexibility,

The bags must provide ESD protection, mechanical strength, and puncture resistance, and they should be heat sealable Additionally, the water vapor transmission rate (WVTR) must not exceed 0.03 g/m² in 24 hours at 40 °C, following flex testing as per national standards for flexible barrier materials The WVTR is determined using national standards that govern the measurement of water vapor transmission through plastic films and sheeting, utilizing a modulated infrared sensor.

The desiccant material must meet national standards for activated desiccants used in the static dehumidification of packaging bags It should be dustless, non-corrosive, and capable of absorbing specified amounts as outlined in the standards.

MECON Limited, located in Ranchi and Bangalore, has received licensed materials for internal use, supplied by the Book Supply Bureau The contents are packaged in moisture-permeable bags, with the amount of desiccant determined by the bag's surface area and water vapor transmission rate (WVTR) This ensures that the interior relative humidity remains below 30% at 25 °C for SMD classification A2, and below 10% at 25 °C for SMDs classified from Levels B2a to B5a.

In comparing different types of desiccants, the term "UNIT" is used as a standard measurement for desiccant quantity A UNIT is defined as the capacity to absorb at least 2.85 g of water vapor at 20% relative humidity (RH) and 25 °C To comply with dry pack standards, it is essential to determine the amount of water vapor a UNIT can absorb at 10% RH and 25 °C.

When the desiccant capacity at 10 % RH and 25 °C is known, the following equation should be used

U = amount of desiccant in UNITS;

M = shelf life desired in months;

WVTR = water vapour transmission rate in g/m 2 in 24 h;

A = total surface area of the MBB in m 2 ;

D = amount of water in grams, that a UNIT of desiccant will absorb at 10 % RH and 25 °C

When the desiccant capacity at 10 % RH and 25 °C is not known, the quantity needed can be estimated using the following simplified equation

U = amount of desiccant in UNITS;

A = total surface area of the MBB in m 2

NOTE If trays, tubes, reels, foam end caps, etc., are placed in the bag without baking, additional desiccant will be required to absorb the moisture contained in these materials

The HIC must adhere to national standards for chemically impregnated humidity indicator cards For level A2, it should demonstrate a sensitivity of 30% RH, which can be represented by color dots indicating sensitivity values of 20% RH, 30% RH, and 40% RH.

SMDs classified from Levels B2a through to B5a, as a minimum, the HIC shall have 3 colour dots with sensitivity values of 5 % RH, 10 % RH, 60 % RH Example HIC are shown in Figure

Below 30% RH can be confirmed by comparison of a color (lavender)

Figure 2a – Example humidity indicator card for level A2

NOT blue Lot num ber

Bake parts if 10 % is NOT blue and 5 % is pink

M anuf act urer’ s ident ifi cat ion

Initial use: Do not put this card into a bag if 60 % is pink

Figure 2b – Example humidity indicator card for levels B2a to B5a

Figure 2 – Example humidity indicator cards

Labels

The dry pack process requires specific labels, including the moisture-sensitive identification (MSID) label and a caution label as outlined in Annex A (refer to Figures A.2 to A.5) The MSID label must be placed on the lowest-level shipping container containing the moisture barrier bag (MBB), while the caution label should be attached to the exterior of the MBB.

Level B6 parts not shipped in MBBs shall have both an MSID label and the appropriate caution label affixed to the lowest level shipping container

Level A1 and B1 components, which are rated for a maximum reflow temperature between 220 °C and 225 °C, must display a caution label indicating this temperature limit This label should be attached to the MBB, if applicable, or to the lowest-level shipping container.

A caution label is unnecessary if a bar code label displays the level A1 or B1 classification along with maximum reflow temperature information in a readable format Specifically, parts classified as level A1 and B1 with a maximum reflow temperature between 220 °C and 225 °C do not need any moisture-related labels.

Shelf life

The calculated shelf life for dry packed SMDs shall be a minimum of 12 months from the bag seal date, when stored in a non-condensing atmospheric environment of 17 mm x 17 mm or any stacked die package (See

96 h As above per package thickness and moisture level

Not applicable As above per package thickness and moisture level

As above per package thickness and moisture level

SMD body thickness Level Bake at 125 °C Bake at 90 °C

At limit of floor life + 72 h at

≤ 2,0 mm B4 34 h 20 h 5 days 3 days 47 days 28 days

≤ 4,5 mm B4 48 h 48 h 10 days 10 days 79 days 67 days

> 17 mm × 17 mm or any stacked die package (See

2-6 96 h As above per package thickness and moisture level

Not applicable As above per package thickness and moisture level

As above per package thickness and moisture level

Tables 2(a) and 2(b) present data for worst-case moulded lead frame SMDs, allowing users to potentially shorten the bake time if supported by technical justification, such as absorption or desorption data This guidance is generally applicable to other non-hermetic SMDs as well.

BGA packages larger than 17 mm x 17 mm, which lack internal planes obstructing moisture diffusion in the substrate, can utilize bake times determined by the thickness and moisture level as outlined in the table.

Table 3 – Default baking times used prior to dry-pack that were exposed to conditions ≤60 % RH (supplier bake: MET = 24 h)

SMD body thickness Level Bake at 125 °C Bake at 150 °C

The specified bake times are based on worst-case scenarios set by suppliers and distributors, acknowledging that oxidation may occur Suppliers may adjust the actual bake time if there is technical justification, such as absorption or desorption data.

Post exposure to factory ambient

Floor life clock

Storing SMDs that have been in factory conditions for over one hour in a dry cabinet or dry pack does not automatically halt the floor life clock However, if the specified conditions in section 6.2.3 are satisfied, the floor life clock can be stopped or reset.

Any duration exposure

Moisture sensitive SMDs exposed to ambient conditions of 60% relative humidity or lower can be effectively dried using high or low temperature baking methods, as outlined in Table 2 for rebaking before reflow and Table 3 for drying before dry packing.

Short duration exposure

6.2.3.1 General considerations for short duration exposure

Previously dry SMDs, which have been exposed only to ambient conditions not exceeding

At 30 °C and 60% relative humidity, materials can be effectively dried using room temperature desiccation methods such as dry packs or dry cabinets When employing a dry pack, the original desiccant can be reused if the total exposure time does not exceed 30 minutes.

For moisture sensitivity levels B2 and B3 with floor life exposure not greater than 12 h at

30 °C/60 % RH, a minimum desiccating period of 5× the exposure time is required to dry the

SMDs enough to reset the floor life clock This can be accomplished by dry pack according to

5.3 or a dry cabinet that is capable of maintaining not greater than 10 % RH

For moisture-sensitive components classified as levels B2, B2a, or B3, exposure for less than their specified floor life can be managed by dry packing or storing them in a dry cabinet with a relative humidity not exceeding 10% RH, effectively pausing the floor life clock However, it is essential that the cumulative floor life adheres to the conditions outlined in Table 4 and/or Table C.2 This guideline does not apply to components classified as level B4.

For moisture sensitivity levels B5 and B5a with floor life exposure not greater than 8 h at

30 °C/60 % RH, a minimum desiccating period of 10× the exposure time is required to dry the

SMDs enough to reset the floor life clock This can be accomplished by dry pack according to

5.3 or a dry cabinet that is capable of maintaining not greater than 5 % RH

Once the floor life clock has been reset, refer to 7.4 for safe storage conditions.

General considerations for baking

High-temperature carriers

Unless otherwise indicated by the manufacturer, SMDs shipped in high-temperature carriers

(e.g., high-temperature trays) can be baked in the carriers at 125 °C.

Low-temperature carriers

SMDs transported in low-temperature carriers, such as tubes, low-temperature trays, or tape and reel, must not be baked at temperatures exceeding 40 °C If a higher baking temperature is necessary, the SMDs should be transferred to thermally safe carriers for baking before being returned to the original low-temperature carriers.

NOTE 1 Manual handling may increase the risk of mechanical and/or ESD damage

NOTE 2 If SMDs are placed in dry bags with unbaked carriers, refer to 5.3.2.2.

Paper and plastic container items

Before baking, it is essential to remove paper and plastic container items, including cardboard boxes, bubble wrap, and plastic wrap, from around the carriers Additionally, rubber bands on tubes and plastic tray ties must be taken off before subjecting the items to high temperatures of 125 °C.

Bakeout times

Bakeout times start when all SMDs reach the specified temperature.

ESD protection

To ensure the safety of ESD-sensitive items, it is essential to follow proper ESD handling precautions in line with national standards This is especially important when manually handling SMDs with vacuum pencils in low-humidity environments, such as dry conditions or after baking.

Reuse of carriers

The appropriate materials specification should be consulted before reusing carriers.

Solderability limitations

Baking surface mount devices (SMDs) can lead to oxidation and intermetallic growth at the terminations, potentially causing solderability issues during board assembly To mitigate these risks, the baking temperature and duration are constrained by solderability guidelines Unless specified otherwise by the supplier, the total baking time at temperatures exceeding 90 °C and up to 125 °C should not surpass 96 hours If the baking temperature remains below 90 °C, there are no restrictions on the baking duration Additionally, baking at temperatures above 125 °C requires prior consultation with the supplier.

Care should be taken to ensure that out-gassing of materials from the component carriers does not occur to any significant extent, such that solderability might be affected

Floor life clock start

When the MBB is opened, the floor life clock begins If the SMDs are not utilized within the designated floor life, it is essential to adhere to the procedures outlined in Clause 6.

Incoming bag inspection

Upon receipt

Inspect dry packed SMDs for the bag seal date on the caution or bar code label Ensure the bags are free from holes, gouges, tears, punctures, or any openings that could expose the contents or an inner layer of a multilayer bag If any openings are detected and the humidity indicator card (HIC) shows that maximum humidity has been exceeded, bake the parts for 48 hours at 125 °C or follow the saturated bake times outlined in Table 2.

Component inspection

Intact bags may be opened for component inspection by cutting at the top of the bag near the seal If the bags are opened under factory ambient conditions, see 6.2.3.

Floor life

The floor life of SMDs, as outlined in Table 4, can be affected by environmental conditions not specified in the table For guidance on the maximum allowable time before rebaking is required, consult Annex C If only partial lots are utilized, any remaining SMDs must be resealed or stored safely within one hour of bag opening, as indicated in section 7.4 Should the one-hour exposure limit be surpassed, refer to section 6.2 for further instructions.

Table 4 – Moisture classification level and floor life

Level Floor life (out of bag) at factory ambient

B6 Mandatory bake before use After bake, shall be reflowed within the time limit specified on the label

Safe storage

Safe storage categories

Safe storage of SMDs requires maintaining dry conditions with controlled humidity to ensure that the floor life clock remains at zero The acceptable storage conditions for SMDs classified as level B2 through B5a are outlined below.

Dry pack

Dry packed SMDs stored in intact MBBs, following the guidelines of section 5.3, are guaranteed a minimum shelf life of 12 months from the date indicated on the caution or bar code label.

Dry atmosphere cabinet

These are storage cabinets which maintain low humidity by purging with dry air or nitrogen at

25 °C ± 5 °C The cabinets must be capable of recovering to their stated humidity rating within

1 h from routine excursions such as door opening/closing

SMDs that are not stored in a moisture barrier bag (MBB) can be kept in a dry atmosphere cabinet with a relative humidity not exceeding 10% However, these dry cabinets should not be regarded as MBBs The storage duration of SMDs in these cabinets must be limited according to the guidelines provided in Tables C.1.

C.2 If the time limit is exceeded they should be baked according to Table 3 to restore the floor life

SMDs that are not sealed in a moisture barrier bag (MBB) can be stored in a dry atmosphere cabinet with a relative humidity of no more than 5% This method of storage is comparable to keeping them in an MBB, allowing for an unlimited shelf life.

Class A2 SMDs that are not sealed in a moisture barrier bag (MBB) can be stored in a dry atmosphere cabinet with a relative humidity not exceeding 30% RH This method of storage is regarded as equivalent to keeping them in an MBB, allowing for an unlimited shelf life.

Reflow

Reflow categories

Reflow includes single and multi-pass assembly reflow and single component attach/removal for rework.

Opened MBB

Once a dry pack (MBB) is opened, all surface mount devices (SMDs) inside must undergo complete solder reflow processing, including any necessary rework, before the specified floor life expires Alternatively, they should be resealed in the MBB or stored in a dry atmosphere cabinet as outlined in section 6.2 If the floor life or factory ambient conditions are surpassed, please consult section 7.6.3 for guidance.

Reflow temperature extremes

During reflow the component body temperature shall not exceed the rated value, stated on the caution label The body temperature during reflow directly influences component reliability

NOTE 1 The component body temperature can be very different from the lead or solder ball temperature, particularly in IR and IR/convection processes, and should be checked separately

NOTE 2 Some hot air attach processes can require heating the component body to very high temperatures If that temperature exceeds the classification temperature, moisture precautions and/or time-temperature limitations beyond the scope of this specification can be required The supplier should be consulted.

Additional thermal profile parameters

During the reflow process, it is essential to adhere to the thermal profile parameters outlined in IEC 60749-30 While the body temperature is the most critical factor, other parameters, including total exposure time to elevated temperatures and heating rates, can also significantly impact the reliability of components.

Multiple reflow passes

If more than one reflow pass is used, care shall be taken to ensure that no moisture sensitive

SMDs, whether mounted or unmounted, have surpassed their floor life before the final pass If any component on the board has exceeded its floor life, it is essential to bake the board before the next reflow For guidance on baking populated boards, please refer to Annex B.

NOTE 1 The floor life clock is NOT reset by any reflow or rework process

NOTE 2 For cavity packages in which water can be entrapped, water clean processes after the first reflow can be an additional source of moisture This can present an additional risk, which should be evaluated.

Maximum reflow passes

A maximum of three reflow passes is allowed per component If more than three are required for any reason, the supplier shall be consulted (see IEC 60749-20).

Drying indicators

Drying requirements

These are events and conditions that require component drying prior to reflow or continued safe storage.

Excess humidity in the dry pack

Excess humidity in the dry pack is indicated by the humidity indicator card (HIC), which can result from misprocessing, such as insufficient desiccant, mishandling that causes tears or rips in the moisture barrier bag (MBB), or improper storage conditions.

The HIC must be read promptly after being taken out of the MBB, ensuring optimal accuracy at a temperature of 23 °C ± 5 °C These conditions are applicable regardless of the storage duration, including instances where the shelf life may have been surpassed.

For SMDs of class A2, if the HIC indicates that humidity inside MBB does not exceed 30 %

RH, the parts are still adequately dry

For SMDs of classes B2a to B5a, if the 10 % RH dot is blue, the parts are still adequately dry

The desiccant shall be replaced by active desiccant if the bag is going to be resealed

For SMDs of class A2, if the HIC indicates that there is a possibility of the humidity inside

MBB exceeding 30 % RH, the SMDs have been exposed to an excessive level of moisture, and drying shall be done in accordance with Clause 6

For SMDs classified from B2a to B5a, the presence of a pink 5% RH dot and a non-blue 10% RH dot indicates excessive moisture exposure Consequently, drying must be performed as outlined in Clause 6.

Floor life or ambient temperature/humidity exceeded

If the conditions for floor life or ambient temperature and humidity outlined in Table 4 are exceeded, SMDs must be dried according to Clause 6 before reflow or safe storage In cases where the factory's ambient temperature and humidity cannot meet the specified conditions, the component's floor life should be derated accordingly For more details on floor life derating, refer to the relevant section.

Level B6 SMDs

SMDs classified as Level B6 shall be dried by baking, then reflowed within the time limit specified on the label

Symbol and labels for moisture-sensitive devices

The purpose of this annex is to provide a distinctive symbol and labels to be used to identify those devices that require special packing and handling precautions

This symbol (see Figure A.1) indicates that devices are moisture sensitive to level A2 or to a level from B2 to B6 and it appears on all moisture sensitive caution labels (see Figure A.4)

Figure A.1 – Moisture-sensitive symbol (example)

A.2.2 Moisture-sensitive identification (MSID) label

The lowest level shipping container must display a label indicating the presence of moisture-sensitive devices It is recommended that this label have a minimum diameter of 20 mm.

A label is mandatory when the classification temperature exceeds 225 °C, and it must be affixed to the lowest level shipping container This label serves to indicate the classification temperature and to identify the devices as “NOT MOISTURE SENSITIVE.”

These devices do not require special storage conditions, provided:

1 they are maintained at conditions equal to or less than 30 °C/85 % RH, and

2 they are solder reflowed at a peak body temperature which does not exceed 225 °C

NOTE Level and body temperature are defined in IEC 60749-20

Figure A.3 – Information label for level A1 or B1 (example)

The moisture-sensitive caution label may be used for level A2 as defined by IEC 60749-20

See Figure A.4 This label is required on the moisture barrier bag and will provide the following information:

• the calculated shelf life in the sealed bag;

• the peak SMD body temperature (top surface) used for device classification as defined by IEC 60749-20;

• the floor life of the device at 30 °C/70 % RH as defined by IEC 60749-20

1 Calculated shelf life in sealed bag : months at 70 % RH (for level A2) or 60 % RH (for level B2a to B5a), use diffusivity 1,320 e - 0,35eV/kT mm 2 ãs –1 (this uses largest known diffusivity at 30 °C)

Table C.1 – Recommended equivalent total floor life (days) for level A2 at 20 °C, 25 °C,

30 °C and 35 °C for ICs with Novolac, biphenyl and multifunctional epoxies

(reflow at same temperature at which component was classified)

Floor Life after opening MBBs whose inner atmosphere is 30 % RH (The values in parenthesis are floor life after opening MBBs whose inner atmosphere is 10 % RH)

SMD type and body thickness

Moisture sensitivity level Maximum percent relative humidity Temperature °C

All TQFPs, TSOPs or all BGAs < 1 mm body thickness

(1) 20 NOTE ∞ represents indefinite exposure time allowed at conditions specified

Table C.2 – Recommended equivalent total floor life (days) for levels B2a to B5a at

20 °C, 25 °C, 30 °C and 35 °C for ICs with Novolac, biphenyl and multifunctional epoxies

(reflow at same temperature at which component was classified)

SMD type and body thickness

Floor life SMD type and body thickness

All TQFPs, TSOPs or all BGAs

Tiêu đề	Handling, Packing, Labelling and Shipping of Surface-Mount Devices Sensitive to the Combined Effect of Moisture and Soldering Heat
Trường học	International Electrotechnical Commission (IEC)
Chuyên ngành	Electrical and Electronic Standards
Thể loại	International Standard
Năm xuất bản	2009
Thành phố	Geneva

Định dạng
Số trang	68
Dung lượng	1,22 MB