It could be zillions of reasons and unless  proper FA is done you are NEVER  going to figure out what exactly caused the problem.
------Original Message------
From: Ramakrishnan Saravanan
Sender: TechNet
To: [log in to unmask]
ReplyTo: TechNet E-Mail Forum
ReplyTo: Ramakrishnan Saravanan
Subject: [TN] corrosion under Solder Mask
Sent: Mar 2, 2013 18:13

Dear all,

We have received few MLBs from a contract supplier. The board was inspected and accepted for wiring. The assembly is for high reliability applications. We conformal coated, tested,thermal cycled and closed the package. We opened the package for some rework, we found corrosion under solder mask on some tracks. 

The corrosion is in the form of  blisters and localized. Center of the tracks or edge or localized and not covering the entire width of the tracks. 

What could be the reason for corrosion under solder mask ?. How to diagnosed for root cause analysis ? regards,

R.Saravanan


Regards,

Vladimir

SENTEC Testing Laboratory Inc.
11 Canadian Road, Unit 7.
Scarborough, ON M1R 5G1
Tel: (647) 495-8727
Cell: (416) 899-1882
www.sentec.ca

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