Hello help.... 

My question is, do you have any knowledge of any studies having been performed regarding reliability of ethchback vs. non, or low etchback on innerconnect joints of polyimide PWBs? 

My customer is asupplier for an aerospace company, and the issue is that they recently have found through microsection analysis that some boards they have already installed in a vehicle are suspect, with regards to etchback.  I am looking for supporting documentation to disposition the boards.  Our requirement is for etchback per 6012 CL III, but I don't believe they are necessarily un-usable. The sections are otherwise structurally sound, no post or plating sep, 1oz and greater conductors, etc.   

As always, I appreciate any info you might be able to pass on. 

Regards, 

Tino Gonzalez