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FEBRUARY 2021 I PCB007 MAGAZINE 77 list, however, there are several deemed worthy of benchmarking and implementing best prac- tices. Rinsing e PCB fabrication wet processes require good quality rinse water and best practice re- garding proper rinsing design. Here again is the quest to reduce cost by cutting back on rinsing. is is not an ideal situation. Yes, it is a hard fact that processing printed circuit boards con- sumes large volumes of a precious resource. However, there are ways to remove contami- nants from the printed circuit board and still conserve water. At first thought, rinsing is oen defined as re- moving process solutions from work, or in the case of the PCB industry, a panel. is is true, if not absolutely true. In general, rinsing is not the complete removal of the contaminants but rather a dilution of a process solution from work (panel) down to "manageable" concen- trations. With this definition in mind, rinsing systems can be designed to minimize harmful contaminants on a printed circuit board and reduce water consumption. I'm oen asked if some "standard" can be applied to the rins- ing process. Are all types of contaminants the same? Is there a hard and fast rule for rinsing? e short answer is, not really. What consti- tutes a "manageable" concentration is depen- dent upon three conditions: • e type of contaminant • e tolerance of the following process step for the particular contaminant in question • e effect the residual contaminants have on the work e bottom line is to use tempered water rins- es, along with sufficient dwell times required to remove the majority of these harmful contam- inants. Counterflow rinses are particularly ef- fective. When rinsing is ineffective (Figure 3), the stark reality of contaminant drag-in to sub- sequent process steps is certain. Consider issues related to the electroless copper metallization process. Inadequate rins- ing aer the micro-etch step will lead to cop- per ion drag-in to the palladium-based catalyst. And it is well documented that high copper Figure 2: Via quality after implementation of best practice. Figure 3: Poor rinsing leading to cleaner drag-in to another key process tank: Significant foam from residual cleaner drag-in.