Hi Lyon, 

I doubt it is a material issue, particularly if the problem is isolated to a specific supplier date code. Is the SM peeling on the Cu, the resin or both? 

Some things to consider:
1. Pre-soldermask cleanliness. If soldermask is peeling off the Cu only, check that the microetch (H2SO4) or the pumice scrub/ alumina (Al2O3) parameters are within spec for that date code. If it's peeling off everywhere it might be contamination. I've seen a PCB shop use city water instead of DI water in the pre-soldermask rinse with very bad results. Most suppliers monitor cleanliness of the pre-SM as a process control using ROSE/Omegameter and, if you're lucky, SIR. Check to see if there are any anomalous readings during this date code. 
2. Cure - Check the oven settings: belt speed, temperature, temp uniformity, airflow.  Sometimes, mysteriously, the temperature and belt speed just happen to increase during crunch times. But hotter and faster may not adequately cure the hardeners. 
3. Thickness - Ensure the SM deposition is not too thick. (PCB shops usually monitor wet thickness). 
4. Stand time - Make sure the SM was properly and adequately mixed, and that max floor time was not exceeded after mixing. 

I'm assuming your PCB assembly process did not change or is not unusually severe. But even low-grade soldermasks should survive 2 reflows and be ready to survive the wave and rework. 

Good luck!
Todd


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of lyonyuan
Sent: Tuesday, April 08, 2014 7:42 AM
To: [log in to unmask]
Subject: [TN] solder mask peel off after Top sider reflow

Hi Team,

 

We found some PCBA boards(the same date code) with solder mask peel off after Top side reflow. Material issue or process issue?

 

Lyon yuan

 



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