Hi Victor,
For optimum reliability, the pad diameters should be 1:1 if either both are SMD [solder mask defined] or neither is SMD; if one is SMD and the other is NSMD, the SMD pad diameter is best at about 1.1-to-1.2:1.
The reason for this is the stress concentration geometry resulting from the solder mask interfering with the surface tension of the molten solder forming a smooth contour.
Having said this, this is more important if you do aggressive accelerated testing or have severe use conditions [automotive].
Werner
Upcoming workshops:
September 21, European Electronics AssemblyReliability Summit, Tallinn, Estonia,
“Solder Joint Reliability-Part 1: Fundamentals in SolderJoint Reliability”
September 21, European Electronics AssemblyReliability Summit, Tallinn, Estonia,
“Solder Joint Reliability-Part 2: Failure Mode and RootCause Analyses (Fatigue, Brittle Fracture, ENIG)”
November 2 & 9, SMTA Webtorial,
“Fundamentals in Solder Joint Reliability”
December 7 & 14, SMTA Webtorial,
“Acceleration Models,Accelerated Reliability Tests and Screening Procedures”
-----Original Message-----
From: Victor Hernandez <[log in to unmask]>
To: [log in to unmask]
Sent: Wed, Oct 20, 2010 12:04 pm
Subject: [TN] Pad to Pad ratio, BGA solder bump
Fellow TechNetters:
Searching for guideline/Industry Standards for solder bump pad ratio. The
carrier external copper pad to PWB/PCB external copper pad. I was initially
given info that the ration should be close to 1:1. Otherwise the formation of
the solder bmp would vary in shape. Also solder mask defined mis-registration
would cause solder bump mis-shape. With this shape difference will an
imbalance of the solder cause stresses occur.
Carrier pad: 12 mil, solder bump dia. 14 mil: PWB/PCB pad: 7 mil
I don't have a cross section yet. Soon I hope.
Victor
Alias Mr. " X "
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of KennyB
Sent: Wednesday, October 20, 2010 10:12 AM
To: [log in to unmask]
Subject: Re: [TN] NTC Friday quiz 21
As some of you may remember I retired two months ago and I highly recommend
it for anybody and the sooner the better! BUT I have not retired from
TechNet, I still lurk around the edges and enjoy reading everything. I
haven't contributed much lately but sure to find "both" Friday challenges
fun and interesting.
YES - Keep it up!
KennyB
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