PPS caps degrading value

we have recently been having trouble with our PPS capacitors on a couple of our boards. these boards are RoHs and the Parts are RoHs compliant. these boards first run through our reflow then a batch washer some through-hole parts are placed and then they are ran through our Wave. I Ran a "test" batch of boards through the whole process, testing them at every avialable step. they didn't fail after reflow or after wash but after wave they started failing, value decreased to .08 uf instead of .1 uf. I ran some profiles on wave and we are not exceeding the temp that the part is spec'd to handle. I ran one part through our wave 5 times and then dipped it in molten solder for 11 seconds and still didn't experience the drastic change in value. I looked at the Technical data sheet for these components and they all said Hallogen could cause a decrease but I placed 10 parts in a cup of our flux (aim ws715m)for 2 hours and none of them decreased in value. Any ideas what could be causing this?????

reply »