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Trouble in Your Tank: The Critical Importance of Rinsing, Part 1

In nearly every chemical process step in the PCB industry, rinsing is an immediate and required process step. Rinsing is typically a crucial step following a chemical process, and is thought to be one that requires little or no attention to function properly. However, problems caused by ineffective rinsing are responsible for many rejects, as well as huge operating costs in the waste treatment department.

It’s a fact: Processing printed circuit boards consumes large volumes of a precious resource. However, there are ways to perform the function of removing contaminants from the printed circuit board and still conserve water.

At first thought, rinsing is often defined as the removal of process solution from the work, or in the case of the PCB industry, a panel. This is true, if not absolutely true. Rinsing, in general, is not the complete removal of the contaminants, but rather a dilution of a process solution from the work (panel) down to manageable concentrations. With this definition in mind, rinsing systems can be designed to minimize harmful contaminants on a printed circuit board and reduce water consumption. I am often asked if there is some standard that can be applied to the rinsing process. Are all types of contaminants the same? Is there a hard and fast rule to rinsing? The short answer is, not really.

What constitutes a manageable concentration is dependent upon three conditions:

1. The type of contaminant

2. The tolerance of the following process step for the contaminant in question

3. The effect the residual contaminants have on the work

Let us examine the contamination, or “dragin,” of an alkaline cleaner into a persulfate-based microetch vs. the same cleaner dragged into an acid copper plating bath.

To read the full version of this column which appeared in the July 2017 issue of The PCB Magazine, click here.