To TechNet Forum Members,
        We are a contract manufacturer who assembles boards in a high mix low to medium volume environment.  The concern I have is over two part numbers which we assemble. One assembly has a .062 thick 6 layer board with vias that have a finish hole size of .013.  The other assembly has a .062 thick 4 layer board with vias that have a finish hole size of .013.  Open vias have been detected on most of the 6 layer boards and about 2% of the 4 layer boards.
I have read some of the responses from the TechNet archives on a similar situation back in 1996.  However, the board house believes that none of the issues addressed are the problem.   The board house is testing the boards on a clam shell fixture using a net list test.  They are using multifunctional material on the 6 layer and varying the material on the 4 layer.  Additionally, they are using the Shadow Process in lieu of electroless plating.  Cross sections are done to production boards prior to shipping and they assure me that the vias have 1 mil of copper on the walls.  The vias are not tented on either board and therefore are supposed to fill with solder.  We are currently having the known open vias cross sectioned by an independent company.
The opens are developing at various stages.  Some boards pass ICT and fail at the customers site during burn in.  Others fail at ICT.  Coincidentally, all of the opens found did not get filled with solder in the assembly process.  It seems that most of the problems are related to connections to the power or ground plane.  However, we have seen a small percentage of open signal connections, but these are primarily developing at the customer's site.  The board vendor has the 6 layer boards AOI before and after pressing the inner layers.  The 4 layer does not receive the same treatment.
Questions:
What PWB manufacturing process could be causing this?
There is no evidence of measling which is usually evident after gross Z-axis expansion, is    there something we can do during the assembly process to help minimize Z-axis expansion?
        How would you proceed with this situation?
Please E-mail any responses to [log in to unmask]  ANY help would certainly be appreciated.

Thank you!
Mark Kray

################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
To subscribe:   SUBSCRIBE TechNet <your full name>
To unsubscribe:   SIGNOFF TechNet
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################

################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
To subscribe:   SUBSCRIBE TechNet <your full name>
To unsubscribe:   SIGNOFF TechNet 
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################