Causes of Delamination ["Quality Assessment of Printed Circuit Boards" Lund, Preben; Bishop Graphics 1985 0137450354] The reason for delamination is epoxy starvation in the glass cloth layers or an incomplete curing of the base material. It has been reported that some manufacturers of laminates have reduced the lamination press cycle a little in order to increase production.
In multilayer boards, visible delamination may be due to poor lamination of layers or insufficient bonding of prepregs to the inner layer copper circuits. Here, the PCB manufacturer is in a way also the "manufacturer" of the base material.
Delamination may develop, however, in a board after assembly and soldering. There are several possible reasons for this: * Asymmetrical buildup of multilayer boards. * Faulty soldering techniques, such as skipping the baking which removes retained moisture from the board. (A 1 to 2 hour baking at 230*F immediately before assembly and soldering is highly recommended. * Lack of preheating as the first step of mass soldering.
A-600 has words to the effect: Delamination or blistering may occur in clad laminate materials either between plies of laminate, or between the laminate and the foil cladding. Any occurrence, either in the as-received condition or after routine thermal stress testing at receiving inspection is evidence of a major flaw, and the material should be rejected, since the defect will almost always propagate during the normal stresses of manufacturing.
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