Plating through hole

Fig. 8. Protection of a plated through-hole in a PWB during etching by using a tenting dry-film photoresist.

A. M. Pesco and H. Y. Cheh, The current Distribution Within Plated Through-Holes I. The Effect of Electrolyte Flow Restriction During DC Electrolysis, J. Electrochem. Soc., 136, No. 2, 399-407 (1989). 

Several techniques can be used to produce the actual conductor paths on the PWB substrate. These techniques are depicted in Figure 1.12. Subtractive processing starts with a PWB coated on one or both sides with copper foil ranging in thickness between 5 and 70 im. In the case of doublesided PWBs containing plated-through holes, the holes are first drilled and... 

PBO and PBZT films can be made very thin (less than 0.002 in.) and can be impregnated with secondary resins, resulting in a substrate with a dielectric constant less than 2.8, an isotropic planar CTE of 7 ppm per °C or less, and temperature resistance over 250°C. Copper circuits and ground planes can be added by a variety of additive or substrative means, and multilayer circuit boards can be fabricated using plated through holes. Further development of these thin film dielectric substrates should result in interconnection density over 100 times greater than is currently possible with fiber reinforced epoxy multilayer boards. 

Some penetration into conventional double-sided, plated through-hole (pth) printed circuit board areas on the basis of pure cost savings in the board cost. 

A cost reduction area that could have significant opportunities for chemicals companies is the interest in cheaper track generation systems such as screen printed conductive inks and the conductive pastes that are being used to replace plated through holes (PTH). Copper-based inks are already being used to form crossovers and simple circuits, and the use of thick film techniques of multiple layer printing is being evaluated to replace some multilayer circuits. 

For many years the standard package was the Dual In Line (DIP) and the plated through hole (PTH) glass... 

Plated through hole multilayer circuit boards, MIL P 55640. Also see Printed wiring for elec tronic equipment, MIL STD 1495. 

Surface-mount technology replaces previous methods of inserting component leads into plated through-holes of PWBs, wave soldering from the back side to flow solder into the holes, and simultaneously forming both mechanical and electrical connections. SMT is highly automated and currently the most widely used production process for the assembly of single-layer, double-sided, and multilayer circuit boards. 

Liou et al. [13] have measured the effect of absorbed moisture on the thermal expansion coefficients of carbon fibre epoxy laminates. Moisture lowers the transverse coefficient, but has little effect on Oi at room temperature. Failure in some epoxy laminates used to make multilayer PCBs has been traced to high z-axis thermal expansion stresses on marginal plated-through holes. Moisture is a factor, and complete drying can sometimes eliminate the problem [14]. 

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