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rigid-Flex board via problems

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rigid-Flex board via problems | 11 January, 2012

With a large number of you out there building rigid-flex boards. I am wondering first what kind of profile do you use and what are you peak temps. I ask these questions because we are finding that our boards have a high moisture level and we are also finding that the via's are failing once they have been exposed to vibration standards for the military. We are trying to resolve this problem any help that you can give is wonderful.

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rigid-Flex board via problems | 12 January, 2012

215 to 220 deg.C peak reflow. We bake then store all PCB's in low humidity cabinets (appox. 3% RH) prior to running.

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rigid-Flex board via problems | 12 January, 2012

How are the vias failing? Barrel crack?

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rigid-Flex board via problems | 12 January, 2012

Isola water pressure. Between a 210°C normal tin lead cycle and a 250°C lead-free assembly cycle, the vapor pressure doubles. Reflow temperature [*C]||Vapor pressure of water [psi] 150||100 200||225 210||260 220||320 230||400 240||480 250||580 300||1240

The vapor pressure is ripping your boards apart. Dry your boards before soldering. Or better yet, buy dry boards and keep them dry.

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rigid-Flex board via problems | 13 January, 2012

I would recommend that you turn toward your PCB supplier probably China and talk to them. You should always bake your boards if this occurs. If you purchase them form a trusted source you should store them in a McDry until you use them if possible. If you are delaminating and cracking VIAs then you have a VERY serious problem.

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rigid-Flex board via problems | 17 January, 2012

The via's are cracking which then is causing all kinds of problems.

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rigid-Flex board via problems | 19 January, 2012

I am wondering if the failurs that people see are discovered right away or when the units are out in the field. Reason I ask this follow up question is the units that are having problems are all returns from our customers. Is there a way to check for this problem before it goes to our customer X-Ray, flying probe, bed of nails. please advise.

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