John,

        This will be a good discussion, but it may interfere with your 
schedule for release of the next revision or 6012.   We certainly have 
seen small cracks between the pads in dual-bllind constructions.  They are 
termed "eyebrow" cracks since they appear above the pads on the blind 
holes.   As long as they are small and located adjacent to the pads, we 
have considered them to be "in the thermal zone" and acceptable.  It would 
be a good step forward to identify this structure and define actual 
accept/reject criteria.

Thanks,
Lance






John Perry <[log in to unmask]> 
Sent by: IPC-600-6012 <[log in to unmask]>
11/09/2009 09:07 AM
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"(Combined Forum of D-33a and 7-31a Subcommittees)" <[log in to unmask]>


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Subject
[IPC-600-6012] Double-Blind Via Construction and IPC-6012C






Hello Everyone,

Recently, we updated the attached IPC-6012C Figure 3-9 to better 
illustrate requirements for laminate anomalies in Zone A and Zone B.

A question has come up regarding laminate anomalies in double-blind via 
constructions.  Please refer to the attached PowerPoint file.  The 
questions are:


*         Are laminate defects in Zone A allowed after thermal stress?

*         Are any defects allowed in the non-thermal stressed condition in 
Zone A?

*         What would be the size of defects allowed?  Would they be the 
same as for standard PTHs?

*         If defects allowed in non-stressed condition is there a minimum 
spacing requirement of resin/glass between layers?

Let's discuss this through this IPC-600-6012 e-mail forum and see if there 
is a need to further update IPC-6012C Figure 3-9 (or duplicate it and 
modify as needed for double-blind constructions).

Regards,

John Perry
Technical Project Manager
IPC - Association Connecting Electronics Industries(r)
3000 Lakeside Drive # 309S
Bannockburn, IL 60015-1249 USA
+1 847-597-2818 (tel)
+1 847-615-7105 (fax)
+1 847-615-7100 (Main)
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www.ipc.org


[attachment "6012c-3-9.jpg" deleted by Lance A Auer/US/Raytheon] 
[attachment "Blind Via Defects 11-08-09.ppt" deleted by Lance A 
Auer/US/Raytheon]