Last time I checked polyimides can lose between 8%-13%, depending on the spec maker..... One of the advantages of using He in some of the IBM TCM module designs was to limit this... Paul Paul Edwards Surface Art Engineering -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D. Sent: Wednesday, August 20, 2008 9:04 AM To: [log in to unmask] Subject: Re: [TN] Flex Material Movement at Assembly I meant to say "dry storage in a dessicator box over an extended period of time could well reduce the overall dimensions." Sorry about that. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D. Sent: Wednesday, August 20, 2008 11:00 AM To: [log in to unmask] Subject: Re: [TN] Flex Material Movement at Assembly Polyimide flex has a great water retention capability. Storage over an extended period of time could well reduce the overall dimensions. Polyester and pen flex also have this propensity, but I believe it is greatest with polyimide. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of John Anselmo Sent: Wednesday, August 20, 2008 10:38 AM To: [log in to unmask] Subject: [TN] Flex Material Movement at Assembly Hi All, A couple of questions concerning flex panel movement at assembly. We were assembling some 2 layer flex parts with a stiffener and noticed some movement (or mis-alignment) of the stencil on the 2nd side. After the 1st side was completed, the panels were stored in a McDry cabinet for 5 weeks before we finished the lot. When we finally did finish the 2nd side, we saw a progressively larger mis-alignment as you went across the panel (from left to right). The mis-alignment was 5 to 7 mils on a 13 mil wide rectangle pad. These parts are 10 up in a 7" x 8" panel (2 rows of 5). So, my questions are; is this type of movement typical? Did storing these in the McDry add to the problem? They were stored on end, not lying flat. Should they have been stored flat? Is there a way to reverse the material movement? Or do we need to complete the whole lot and not store any in the McDry? What is the time limit (and conditions) for storing panels that haven't been completed? We washed a few panels then baked at low temp (50 deg C) for 15 minutes, and this helped a little. Just need to know if anyone else has experienced this before. 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