AN-2029

Handling & Process Recommendations Handling & Process Recommendations National Semiconductor Application Note 2029 Martin Schnepf June 18, 2010 Introduction This Application Note provides recommendations for handling, storing and mounting of National Semiconductor’s surface mount IC packages. The final manufacturing yield and board level reliability are influenced by various factors and processes outside the control of the IC manufacturer. This Application Note can therefore only be used as a guideline and reference to support our customers. Due to the variety of possible board assembly materials and equipments, National Semiconductor Corporation (NSC) advises the user to consult the individual suppliers and vendors to achieve the optimum board assembly yield. Moisture Sensitivity Level Due to the hygroscopic nature of the plastic encapsulants, the plastic ICs absorb a certain amount of moisture. When subjecting a SMT device to reflow soldering process (e.g. infrared, convection, vapor phase), the entrapped moisture inside the package can create excessive internal pressure resulting in delamination or even cracked package (popcorn effect). NSC’s components that are considered moisture sensitive are sealed in moisture barrier bags (MBB) together with a desiccant and a Humidity Indicator Card (HIC). National Semiconductor generally follows Industry Standards IPC/ JEDEC J-STD-020 and J-STD-033 to determine the moisture sensitivity level and corresponding floor life time for NSC’s plastic package types, for details on absolute maximum ratings for soldering see www.national.com/ms/MS/MSSOLDERING.pdf. The floor life time is the maximum time period from the opening of the MBB to the final reflow soldering process. The MSL Level and floor life time as per Table 1 is provided on NSC’s immediate and/or intermediate packing container label. Additionally, the MSL level and the maximum peak package temperature for National’s devices can be found within the Product Folder of National’s website. TABLE 1. Moisture Sensitivity Levels (According to IPC-JEDEC J-STD-033B.1 (Note 1) MSL Level 1 2 2A 3 4 5 5a 6 Floor Life (out of MBB) Time Unlimited (no moisture barrier bag) 1 year Conditions ≤ 30ºC / 85% RH ≤ 30ºC / 60% RH 4 weeks ≤ 30ºC / 60% RH 168 hours ≤ 30ºC / 60% RH 72 hours ≤ 30ºC / 60% RH 48 hours ≤ 30ºC / 60% RH 24 hours ≤ 30ºC / 60% RH Mandatory bake before use. After bake, must be reflowed ≤ 30ºC / 60% RH within the time limit specified on the label Storage and Shelf Life Solderability tests were conducted on components after long term storage in warehouse conditions and after exposure to accelerated aging environment. Based upon the results, NSC’s shelf life of dry-packaged moisture sensitive devices inside the unopened moisture barrier bag is 3 years after original seal date when stored in an environment not exceeding 40ºC / 90% RH. Component storage outside the MBB should be done in a dry storage cabinet at < 25°C and < 10% R.H. to prevent any moisture absorption. The shelf life with regard to soldering of non dry-packed devices, i.e. MSL1, is 3 years provided the storage environment is controlled at ≤ 30ºC / 85% RH. Please be aware that e.g. bare die & wafer products have different storage conditions and limitations. Reflow Soldering The most popular soldering method for surface mount devices is forced convection reflow and therefore the topic of this chapter. Other possible solder processes for surface mount devices are, with restrictions, infrared reflow (IR), vapor phase and wave soldering. It is not possible for an IC manufacturer to provide a general reflow profile recommendation for the end customer in charge of the board assembly. Reflow furnace settings depend for example on the number of heating/cooling zones, type of solder paste/flux used, board and component size as well as component density. The actual temperature setting needs to be above the liquidus temperature (solder melting point) of the solder paste in order to form a reliable solder joint, while the upper limit is clearly defined by the maximum peak package body temperature depending on package thickness and volume as provided by IPC /JEDEC J-STD-020, see Table 2 and Table 3 AN-2029 Note 1: Copyright IPC/JEDEC. Reproduced with permission. © 2010 National Semiconductor Corporation 301141 www.national.com AN-2029 TABLE 2. Maximum Peak Package Body Temperature Tp (according to IPC-JEDEC J-STD-020D) For Pb-Free Process (Note 1) Package Thickness 2.5 mm Volume < 350mm3 260 °C 260 °C 250 °C Volume 350-2000mm3 260 °C 250 °C 245 °C Volume > 2000mm3 260 °C 245 °C 245 °C TABLE 3. For SnPb Eutectic Process (Note 1) Package Thickness 72 h 5 hours 7 hours 9 hours 11 hours 18 hours 21 hours 27 hours 34 hours 48 hours 48 hours 48 hours 48 hours Exceeding Floor Life by Bake @ 90°C ≤5% RH Exceeding Floor Life by >72 h 17 hours 23 hours 33 hours 37 hours 63 hours 3 days 4 days 5 days 10 days 10 days 10 days 10 days Exceeding Floor Life by Bake @ 40°C ≤5% RH Exceeding Floor Life by >72 h 8 days 9 days 13 days 15 days 25 days 29 days 37 days 47 days 79 days 79 days 79 days 79 days Exceeding Floor Life by ≤72 h 3 hours 5 hours 7 hours 7 hours 15 hours 16 hours 17 hours 20 hours 48 hours 48 hours 48 hours 48 hours ≤72 h 11 hours 13 hours 23 hours 23 hours 2 days 2 days 2 days 3 days 7 days 7 days 8 days 10 days ≤72 h 5 days 7 days 9 days 9 days 20 days 22 days 23 days 28 days 67 days 67 days 67 days 67 days Thickness 2 2a 3 4 ≤1.4 mm Thickness >1.4 mm 2 2a 3 4 2 2a 3 4 ≤2.0 mm Thickness >2.0 mm ≤4.5 mm Note: For BGA package types >17x17mm, stacked die packages or packages with thickness > 4.5mm, please contact your local NSC sales representative 3 www.national.com AN-2029 Repair In case repair or even replacement of a component is needed, it is important that the temperature used for repairing, desoldering or replacing the component, needs to be selected as low as possible to avoid any damage to the adjacent components or PC board. The repair profile should be similar to the actual reflow profile, common rework tools are either hot gun or available rework machines. In addition, depending on the MSL level of the component and if the floor life time from initial reflow soldering process to the repair process is exceeded, a baking process is required with parameters provided in IPC/JEDEC J-STD-033B.1. Otherwise, the accumulated moisture can cause damage as described in the previous chapters. Proper handling practices are required to prevent any ESD damages during any handling of the components. Permissions Note 1: Copyright IPC/JEDEC. 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