Jack,

 

Based on additional information the landscape has changed, I thought it
was an anomaly. I assumed it was in the cross-section of a coupon and
IPC looks at this as a pin hole in a ground area. You have enough
evidence to suspect that the lot has an issue with an etch down
condition that does not withstand thermal excursion process as the
copper trace does not have enough metal mass to move with the Tg of the
material. This may explain why the boards pass electrical test at the
fabrication house. With your additional information it appears the
problem is much wider spread. If this condition is from the board it
appears that the etch down condition may be more wide spread. If the
condition you showed in the section is on a trace it will lead to
electrical opens as the board goes through thermal excursions. 

 

________________________________

From: Jack Olson [mailto:[log in to unmask]] 
Sent: Thursday, February 07, 2008 10:28 AM
To: Kerry Bode
Cc: TechNet E-Mail Forum
Subject: Re: [TN] FAB: Thin Trace Failures

 

Thanks for the response.

 

We have random failures on assemblies that have been 

heated up, only on one batch of boards. 

The guy doing the cross-section implied that he found this

almost by accident. By recommending a "referee" sample

are you saying we should we see the same thing in the 

same spot on a different board (from the same lot)?

 

I'm curious how you could accept this condition on planes

and not suspect that there would be trace layers with the 

same condition. 

 

I'm not disputing what you say, just trying to understand...

 

Jack


 

On 2/7/08, Kerry Bode <[log in to unmask]> wrote: 

Jack,

This condition is most likely to occur when the board fabricator was
processing the inner layer. The resist coating used for imaging may have
had an air pocket at that location causing a lifted resist condition.
Then during the etching process the chemical etch solution undercut the
resist. From my prospective this is an anomaly and is classified as an
etch down condition. If the remainder of the sections do not exhibit the
condition, a referee cross-section of the same serial number would
acceptable. Based on the cross-section photo it appears to be a ground
or power layer, if so IPC specification allowance for this condition.

Regards

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Jack Olson
Sent: Thursday, February 07, 2008 8:33 AM
To: [log in to unmask]
Subject: [TN] FAB: Thin Trace Failures

Has anyone ever seen a cross-section like this?

http://www.frontdoor.biz/PCBportal/opentrace.jpg

(ignore the words on the pic, just a guess)

Can you point me in the right direction for cause?

thanks,
Jack

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