TechNetters, we've been working here with some large BGA and CGA packages.  One had over 800 columns, for example.  What tools are available to measure the coplanarity of the solder balls or columns on such devices?  And in the case of solder balls, which I presume get relowed, how critical is the planarity of the chip-carrying substrate?  My thought is that if the chip carrier is bowed, a solder ball attached to the center could be coplanar with the others, but represent a lot of solder that could lead to shorting.  

And regarding the PCB itself, how do we measure its flatness with a precision and accuracy to assure it is OK to use with a BGA?  The IPC test method I'm familiar with seemes oriented to measure bow and twist in the range of 0.1% and up, which may not be good enough for BGA work.

Any comments would be appreciated.

Lou Hart
Quality Assurance Manager
Compunetix  412-858-6184

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