Hi Dee,
The answer to your question is going to be application specific. If you don't have it already, I'd recommend you obtain a copy of the following:
* IPC-7095 (Design and Assembly Process Implementation for BGAs)
A good deal of the reliability concerns associated with BGAs can be attributed to ball solder joint cumulative fatigue damage due to thermal cycling (on/off operation of the device, diurnals, temperature swings, etc.). This is largely driven by your end use thermal environment (application).
To this end, the following resources may be of some help:
* IPC-D-279 (Design Guidelines for Reliable Surface Mount Technology Printed Board Assemblies), Appendix A (Design for Reliability (DfR) of Solder Attachments).
* Global SM&T Packaging Magazine - September 2009 Issue, pages 36-39, "Pb-free solder creep-fatigue reliability models updated and extended" by Werner Engelmaier.
If you are unfamiliar with the topic of BGA solder joint reliability and the associated impact of lead vs lead-free solder, it might be worth it to bring in a consultant to help.
One suggestion:
http://www.engelmaier.com/
As Jeff already mentioned the choice of lead vs. lead-free solder influences the choice of board material, part selection and the board/cca manufacturing process. Given the large amount of historical data available for PbSn assemblies, and the relative lack for Pb-Free, re-balling of the BGAs and keeping the CCA a leaded solder assembly may merit serious consideration.
You could also consider underfilling the BGAs to increase solder joint reliability.
R/
Ken Harp
Mechanical Engineer
425.376.4423
[log in to unmask]
Powering your future
-----Original Message-----
From: Dee Stover [mailto:[log in to unmask]]
Sent: Thursday, June 10, 2010 7:13 AM
To: [log in to unmask]
Subject: [DC] rohs, BGAs & assembly
Hi all,
I need to find some written data on the long term reliability of rohs
assemblies. We don't have comply with rohs but can only get the
parts in rohs, with BGA's being the main drive for rohs compliant solder.
Just had an assembly vendor say that a rohs bga can be assembled with
eutectic solder paste with good results. 2 other assembly shops say
that is not recommended. Is there any real studies or data available
that provides the real answer? Also studies and data for the
reliability of rohs? We need our boxes to work for 10 years or more.
Thank you for your time. What a great network for people to share
knowledge. I will also be going through PCD&F and google to
(hopelessly behind on my reading)
:-) Dee Stover [log in to unmask] 520-318-8489
Tech Associate II
National Optical Astronomy Observatories
www.noao.edu
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