Mike,

Where are the vias cracking? Are you seeing a barrel crack or is the crack occuring on the internal trace/pad protruding into the hole wall plating?

A higher temp resin will help if the cracking is due to z-axis expansion. If the crack is on the actual pad / trace and not in the barrel then I would recommend looking into the type of copper foil being used on the innerlayer. A high elongation copper foil should be used.
In addition, you might want to ask your supplier to look at his copper purity and elongation test results from the copper tanks. Some contaminates can make the copper plating brittle and more susceptible to cracking.

As far as baking prior to reflow, I believe most lines process the boards thru a cleaning solution and then flux prior to reflow. This would cool the board and nullify any effect the prebake may have had. It is my experience that prebake is really only effective for driving our any potential moisture entrapment. 

 
Hope this helps. 


Ed Cosper
Director Quality Assurance and Engineering
Graphic Electronics Inc.
Tulsa OK

----------
From:  MICHAEL DODSON[SMTP:[log in to unmask]]
Sent:  Wednesday, January 07, 1998 4:04 AM
To:  [log in to unmask]
Subject:  [TN] Cracked Vias

Hello,

My name is Myke Dodson and I would like
to request feedback from individuals that have experience in dealing
with "Cracked Vias" due to Z-axis expansion.

My scenario deals with an .093" board with vias drilled at .0145".
Standard FR4 material. There is sufficient copper in the hole (.001")
and there are not multiple vias that are cracking. ( i.e. 2 brds
out of 100 ).

Will higher temp material help ?
Will baking prior to assembly help ?
What is your experience with boards that have cracked vias ?
Possible solutions or suggestions.

Please send all responses to: [log in to unmask]
Phone: 408-978-8992 ext.266

Thank you,
Myke Dodson

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