Layer multiple mask

Manufacture of Printed Wiring Boards. Printed wiring boards, or printed circuit boards, are usually thin flat panels than contain one or multiple layers of thin copper patterns that interconnect the various electronic components (e.g. integrated circuit chips, connectors, resistors) that are attached to the boards. These panels are present in almost every consumer electronic product and automobile sold today. The various photopolymer products used to manufacture the printed wiring boards include film resists, electroless plating resists (23), liquid resists, electrodeposited resists (24), solder masks (25), laser exposed photoresists (26), flexible photoimageable permanent coatings (27) and polyimide interlayer insulator films (28). Another new use of photopolymer chemistry is the selective formation of conductive patterns in polymers (29). 

Figure B3.2.3 Electroblotting with a semidry transfer unit. In most cases, the lower electrode is the anode, as shown. Position the Mylar mask (optional) directly over the anode. Layer on three sheets of filter paper that have been wetted in transfer buffer. For negatively charged proteins, place the preequilibrated transfer membrane on top of the filter paper followed by the gel and three additional sheets of wetted filter paper. If multiple gels are to be transferred, separate the transfer sandwiches by inserting a sheet of porous cellophane or dialysis membrane between each stack. Place the cathode on top of the assembled transfer stack(s). Transfer the proteins by applying a maximum current of 0.8 mA/cm2 gel area.

Fig. C.ll. One strategy for consolidating multiple layers onto a single mask. Using rotation instead of lateral translation allows a wider range of die sizes to be used.

Another limitation is posed by the shadowing effect in PMC. The delamination closest to the transducer will reflect the ultrasonic pulse to such an extent that delaminations below will be masked, unless their lateral size is larger. Even C-scans taken on both sides do not necessarily guarantee detection of delaminations in all layers. In the reflection mode, repeat echoes from multiple reflections have to be distinguished from real indications, especially in relatively thin PMC shells. 

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