The Big Picture of HWPA

摘要

In the last column, significant time was spent on the mechanics of the desmear process and issues that cause hole-wall pullaway. This time we look at other, subtler causes of the defect. However, desmear parameters for higher performance resins will be discussed first. In order to resolve HWPA with the more chemically resistant resin systems such as FR-5, BT and FR-4 materials in the 170-180 Tg range, a new approach to sensitizer (solvent swell) chemistry was developed. This patented system was engineered through a careful selection of biodegradable solvents with a specific range of solubility parameters. By carefully matching the solubility parameters of the solvent(s) to the resin system, optimum penetration was achieved. Through optimum solvent/resin interaction, the permanganate was more efficient at micro-roughening the topography and removing sufficient amount of resin. Standard, commercially available systems did not meet the strict criteria of topography enhancement. Thus, the new system had to be developed for resin removal on high-performance resins to be successful. It is quite evident that the modified solvent swell system is necessary for adequate texturing and resin removal for some of the more chemically resistant materials. TABLE 1 shows the degree of resin weight loss using the standard solvent system and the modified process.