Abstract
Approximately two years ago, electro-deposited (ED) copper foil cracking was noticed when testing relatively high density, highly stressed multilayer boards (MLBs) to the rigid 55()°F thermal stress test requirements of MIL-P-55640 and eventually MIL.-P-551 IOC. This ED copper foil cracking is basically caused by severe plated through hole (PTH) bending forces caused by the large difference in thermal expansions between the copper PTH barrel and the epoxy glass resin within the multilayer board at high soldering lemperatures. The severity of the copper foil cracking would be dependent on the basic thermal mismatch of MLB materials; the severity of thermal exposure; the specific design impacts; and the mechanical properties of the copper foil. Copper foil cracks develop circumferentially around the PTH barrel within the relatively weak columnar grain boundaries of the ED copper foil. Generally, cracks occur quite close (within 2 mils) of the PTH barrel wall with cracking or fracturing being more dominant on the first and last internal foil layers within the board.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call