PCB007 Magazine

PCB007-Dec2018

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100 PCB007 MAGAZINE I DECEMBER 2018 Surface preparation and cleaning are essen- tial aspects of metal finishing and PCB fabrica- tion. The PCB fabricator has several process- es that fit the broad category of cleaning and surface preparation. However, the organization needs additional studies to enhance the broad portfolio of products for their respective fit- ness for use in today's technology. In addition, this exercise will assess gaps in the RBP clean- ing and surface preparation segment and make necessary process improvements through bench scale and field application trials. Overview In general, surface preparation is done to en- sure good adhesion of metal, dielectric, photo- resist, or solder mask to the prepared surface, although avoiding excessive adhesion could also be the objective. Take the example of sur- face preparation before dry photoresist lamina- tion, such as failure to: • Achieve good adhesion in a print-and-etch process, which will cause etchant attack under the resist and ultimately an open defect • Achieve good adhesion in a plating process, which will cause tin and lead underplating, ultimately leading to shorting defects (shorts) • Achieve a good release of unexposed resist during development, which can cause etch retardation in a print-and-etch process, ultimately leading to shorts • Achieve a good release of unexposed resist during development in a plating process, which can cause poor adhesion of the plated copper to the copper base (copper-copper peelers) • Achieve a good release of exposed resist in a print-and-etch process on inner layers, which can inhibit the formation of a multilayer bonder on such a copper surface • Achieve a good release of exposed resist in a plating process, which can cause etch retardation • Remove residues including chromates and organic soils (including resin spots), which will adversely affect inner layer bonding and plating quality Figure 1 depicts an example of both an open and a short due to improper surface prepara- tion leading to poor adhesion. To fully grasp some of the surface prepara- tion issues, a primer on the copper foil man- ufacturing process will enhance the read- er's understanding with the composition and topography of standard electrodeposited (ED) and reverse-treated foils (drum-side-treated foils). Surface Preparation and Cleaning, Part 3 Trouble in Your Tank by Michael Carano, RBP CHEMICAL TECHNOLOGY Figure 1: Short circuit (L) and open circuit (R) due to insufficient resist adhesion.

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