I agree Werner, the black pad venom. Can be fixed by Mid - P process.
This is so accurate
From: Werner Engelmaier /* <[log in to unmask]>
Date: Fri, 4 Jul 2008 22:33:12
To: <[log in to unmask]>
Subject: Re: [TN] [LF] [TN] SN100 for Reflow Application
First, I would suggest you use a different lab in the future, or get them
educated. The statements: " The presence of intermetallic at the interface shows
that a “Black Pad” condition is not present." is pure nonsense.
Essentially, but not exclusivley, 'Black Pad' requires that IMCs are formed—th
at enriches the P-content at the Ni/IMC interface.
Second, the fact that you have 3 different failure modes—pad cratering,
brittle interfacial separation, & BGA-side cracks, occuring, sometimes in
combination, shows that you do not have a significant weak link. Some of the
RoHS-capable PCB base materials are more brittle with lower cohesive strength, but
seeing multiple failure modes indicates that is not the issue.
Third, you do not tell me what other processes follow reflow—however,
whatever it is puts significantly higher stresses on the SAC-SJs than on the
CONCLUSION: The root cause is obvious—it is the switch from SnPb to SAC and
ALL that entails.
CRITICAL DIFFERENCES: A) SAC is about 40% stiffer than SnPb=>higher stresses;
B) delta-T to Tg of SAC Solidus v. SnPb Solidus is more than double=>higher
C) delta-T to Tg of SAC Soldering T's v. SnPb Soldering T's is more than 50%
higher causing more warpage=>higher stresses;
D) SAC creep rates are about 50x slower than SnPb=>higher stresses.
I would suggest attending my new workshop Pb-Free Soldering Processes—
Survival, Quality, Reliability.
Pb-Free Soldering Processes—Survival, Quality, Reliability, July 17/18, Thal,
Pb-Free Soldering Processes—Survival, Quality, Reliability, August 18,
Reliability Issues with Lead-Free Soldering Processes, September 22,
Failure Mode and Root Cause Analyses Reliability (Fatigue, Brittle Fracture,
ENIG), September 22, Schaumburg
Solder Joint Reliability: Parts 1 & 4, Oct. 9, Moscow, Russia
Solder Joint Reliability: Parts 1 & 4, Oct. 17, Timisoara, Rumania
Solder Joint Reliability: Parts 1 & 4, Oct. 22, Tallinn, Estonia
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