Dale,

Below are recommendations and should be taken as that.

The first place I would look to find what the root failure of the via is.  Various things could cause this, sometimes more than one.   A few possible avenues:

Design level:
*wrong size pads for design
*wrong material for style of design and final assembly of pwb - could cause issue more at assembly level, certainly with lead-free and low Tg/Td material
*Are the boards 100% netlist tested at the fab vendor before assembly?
At this level, review the notes, the design and know the material being called out.

Fab level:
*poorly drilled holes - improper cleaning of the holes
*worn drill bits
*improper plating in the holes
*old material, check the date of manufacture of the material and how it's been stored.  Some board material is age and water sensitive and this will effect process.
*Were the boards 100% netlist tested before going to assembly to see if they were good to begin with?
*Are the failures occurring in random places in one particular area, it can be clue

To check the fab level, I'd recommend a cross section of the vias that are of issue on a failed device, this will tell you a ton.  It should be done to a bare pwb (unassembled), but it would be no longer repairable or usable.

Assembly level:
*Check the board material to see if it can handle the reflow temp process that was used, whether it be lead or lead-free.  
*review the reflow profile, maybe it's too high in temp or too long.
*maybe the board is being flexed during assembly.  Should it be thicker for the physical size?  I'm just guessing with no dimension size. 

Again I'd recommend a cross section of an afflicted board of the vias in question.  

The main purpose of all this is start narrowing down the possibilities.  Obviously it is something, whether it be design, fabrication, or assembly.  

Hope this helps some,

-JJ

________________________________________



 
JEFFREY A. JENKINS
SR. PCB/CAD Designer CID+
L-3 COMMUNICATIONS-LINKABIT DIVSION
3033 Science Park Rd. 
San Diego, CA 92121
Tel:  (858) 552-9832
Fax:  (858) 552-9487
[log in to unmask]


________________________________________
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Potter, Dale
Sent: Tuesday, September 23, 2008 8:23 AM
To: [log in to unmask]
Subject: [DC] Barrel Cracking on 0.2mm vias

I am looking for some information, studies, past experience, whatever I can find for information about barrel cracking in small diameter vias (0.2mm) on an 8 layer, 1.6mm pcb. I am having a very large issue with this and I am unsure at this point if the problem lies in the use of the 0.2mm vias, the manufacturers abilities, the materials being used, etc.

If someone has some information they can point me to, it would be greatly appreciated!! I need to find out what we/I can do to increase the reliability of the vias.

Dale R. Potter
Associate Product Engineer
 

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