Blind Via With Smaller Solder Mask Opening
Printed From: PCB Libraries Forum
Category: Training / Events
Forum Name: PCB Design Basics
Forum Description:
URL: https://www.PCBLibraries.com/forum/forum_posts.asp?TID=1110
Printed Date: 03 Nov 2025 at 8:19pm
Topic: Blind Via With Smaller Solder Mask Opening
Posted By: NB168
Subject: Blind Via With Smaller Solder Mask Opening
Date Posted: 18 Sep 2013 at 6:04pm
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Hi, Have received a design file from customer for layout modification, this is a HDI designer and the previous designer has created blind via (L8-L7) for the 8 layers board with small solder mask opening. The drill for this blind via is 0.1mm, pad is 0.3mm and the solder mask opening is 0.2mm. These vias are under the BGA.
Any idea what is the intention of previous designer of opening the solder mask under the BGA, now the board is fabricated and we are worry of short under the BGA and need to re-do the fabrication with the solder mask close and affected our schedule.
 Any suggestion on rework on the existing board or the rationale of the open solder mask of the previous designer.
Thanks,
NB
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Replies:
Posted By: Tom H
Date Posted: 18 Sep 2013 at 7:04pm
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All vias under BGA's need to be "Tented" with solder mask to prevent solder bridging under the component. I did the same thing once and the bare boards got to assembly and rejected. Tried to go back to the fabrication shop but they turned me down saying that the solder mask has been cured and there was nothing they could do. So I contacted a different assembly shop and they said "No problem, bring in the bare boards and we'll touch up the exposed vias with a special mask material that we'll manually apply and oven cure". I only wish I would have written down the name of the mask material, but I didn't because I knew from that day forward I would never have exposed vias under a BGA. It cost extra and delayed the delivery, but I did not have to rebuild the boards. ------------- Stay connected - follow us! https://twitter.com/PCBLibraries" rel="nofollow - X - http://www.linkedin.com/company/pcb-libraries-inc-/" rel="nofollow - LinkedIn |
Posted By: NB168
Date Posted: 19 Sep 2013 at 2:05am
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Hi Tom,
Do you remember the assembly shop that you sent to for touch up? Possible to send the contact please. Many thanks.
Best Regards,
NB.
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Posted By: Tom H
Date Posted: 19 Sep 2013 at 7:44am
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It was in San Diego, CA about 10 years ago. I don't remember their name. They said it was no big deal. I'm sure you can Google an answer. ------------- Stay connected - follow us! https://twitter.com/PCBLibraries" rel="nofollow - X - http://www.linkedin.com/company/pcb-libraries-inc-/" rel="nofollow - LinkedIn |