Baking from 24hrs change to 16hrs Reliability plan

Brian

各位前輩先進好~
如果有Module(長29.5mm*寬22.0mm) Baking要從24hrs變更到16hrs,可靠度實驗要如何設計?要怎麼做?
Module相關的資訊如下:
1.The MSL of module is level 4 (Reference Document : IPC-JEDEC J-STD-033).
2.The baking temperature is 125ºC for 24hours or 60ºC for 13 days.
3.The allowable time period, after removal from a moisture barrier bag and before the solder reflows process, for a moisture-sensitive device to be exposed to a factory ambient not exceeding 30°C and 60% RH.
4.After the PCB is baked, it will be expired after 72 hours. Do the SMT process within 48 hours after baking is the best condition.
以上懇請多多指教~Thanks a lot.

liaojenyi

Using Kelvin for baking Temp., by Arrhenius rule
1. AF1 =13 = exp[Ea/8.625E-5*(1/333-1/398)]; ==> Ea = 0.451
2. AF2 = 24/16 =1.5 = exp[0.451/8.625E-5*(1/398-1/Tacc)]; ==> Tacc = 410.6 K = 137.6 C

hlperng

J-STD-020, Moisture/Reflow Sensitivity Classification for Nonhermetic Solid State Surface Mount Devices

5.4 Bake. Bake the sampe for 24 hours minimum at 125 +5/-0 °C.  This step is intended to remove moisture from the package so that it will be "dry".

Table 5-1 Moisture Sensitivity Level. ...  

Level 4: Floor Life = 72 hours @ ≤ 30 °C/60 %RH.  ⇒  Test @ 30 °C/60 %RH for 96 hours or Test @ 60 °C/60 %RH for 20 hours (E_a=0.40 eV ~ 0.48 eV) or 24 hours (E_a=0.30 eV ~ 0.39 eV) 

72 hours = 96 hours - 24 hours (MET)

MET = Semiconductor Manufacturer's Time.  Default MET = 24 hours. 

Note 1. ... Alternatively, if the known activation energy for moisture diffusion of the package materials is in the range of 0.40 eV ~ 0.48 eV or 0.30 eV ~ 0.39 eV, the "acceleration equivalent" may be used. ...

• 0.40 eV ~ 0.48 eV  ⇒ 0.445 eV
• 0.30 eV ~ 0.39 eV ⇒ 0.35 eV

J-STD-033, Handling, Packing, Shipping and Use of Moisture/Reflow Sensitive Surface Mount Devices

4. Drying

Table 4-1, 4-2 and 4-3 give reference conditons for drying SMD packages.  Table 4-1 gives conditions for rebake of SMD packages at a user site after the floor life has expired or other conditions have occurred to indicate excess moisture exposure.  

Package Body Thickness determines the Bake Conditions. (Bake Temperature and corresponding bake time)

For MSL=4, 

If Thickness ≤ 1.4 mm, Bake @ 125 °C for 11 hours (Floor Life > 72 hours) or 7 hours (Floor Life ≤ 72 hours); or Bake @ 90 °C ≤ 5 %RH for 37 hours (Floor Life > 72 hours) or 23 hours (Floor Life ≤ 72 hours); or Bake @ 40 °C ≤ 5 %RH for 15 days (FLoor Life > 72 hours) or 9 days (Floor Life ≤ 72 hours)

For Thickness >1.4 mm and ≤ 2.0 mm, Thickness > 2.0 mm and ≤ 4.5 mm, and BGA Package > 17 mm x 17 mm or any stacked die package, See Table 4-1. 

4.2.7.1 Oxidation Risk.  

... Unless otherwise indicated by the supplier, the cumulative bake time at a temperature greater than 90 °C and up to 125 °C shall not exceed 96 hours. ... Bake temperatures higher than 125 °C are not allowed without consulting the supplier.

7. Derating due to Factory Environmental Conditions

...

1. Activation Energy for Diffusion E_a= 0.35 eV (smallest known value) (NOTE. 濕度擴散的活化能FIDES建議值為0.90 eV。)

2. For ≤ 60 %RH, use Diffusivity = 0.121 exp ( - 0.35/KT) mm²/s (this uses smallest known Diffusivity @ 30 °C)

3. For ≥ 60 %RH, use Diffusivity =1.320 exp ( - 0.35/KT) mm²/s (this uses largest known Diffusivity @ 30 °C)

Appendix B.

...

2. Diffiusivity = 6.2 exp (- 0.445 /KT)  ⇐  E_a = 0.445 eV

參考資料：

• J-STD-020D.1, Moisture/Reflow Sensitivity Classification for Nonhermetic Solid State Surface Mount Devices, 2008.
• J-STD-033B, Handling, Packaging, Shipping and Ues of Moisture / Reflow Sensitive Surface Mount Devices, 2005.
• R.L. Shook and J.P. Goodelle, Handling of Highly-Moisture Sensitive Components - An Analysis of Low-Humidity Containment and Baking Schedules, ECTC, 1999, pp. 809-15. Paper Referenced in Appendix B of J-STD-033.