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FEBRUARY 2021 I PCB007 MAGAZINE 81 e temperature has a significant influence on chemical reactions and rinsing. Solution Agitation Proper agitation and solution movement im- proves the efficiency of rinsing as well as im- proves plating distribution and uniformity. For best practices, the following rules apply: Mechanical agitation for PTH processing: 1. Baskets/Racks • Should be ridged to withstand the vibration energy • Needs to hold the panels tightly so they don't move 2. Spacing • < 0.059" @ 0.5" • 0.060–0.125" @ 0.5–1.0" • 0.125–0.250 "@ 1–2" • >0.250" @ 2" 3. Agitation (Rack) • 2- to 4-inch stroke on center • 14–16 revolutions/minute For Electroplating Processes: is will depend on the electrolyte. Elec- trolytic copper responds very well to eductor- type agitation. Eductor agitation is based on the Venturi Principle, whereby one volume is pumped, and up to four volumes are drawn-in by the pressure drop, making it a highly effi- cient jetting system. When fully submerged, no air is introduced into the plating solution. Sev- eral manufacturers market eductors. Eductor agitation overcomes several of the disadvan- tages associated with air agitation. Air bubbles and misting are eliminated. In addition, educ- tor agitation provides a more uniform mixing of the plating solution. is minimizes poten- tial "dead spots" in the cell where the air agita- tion is lacking. It is well known that educators provide more uniform agitation, better known as laminar flow. In contrast, air agitation provides turbulent flow and may only promote the mixing of the solution. For quality plating results, it is pref- erable to have interface agitation. at is, one interface agitation is directed more at the cath- ode diffusion layer. is reduces the diffusion layer thickness, thus permitting the efficient delivery of additives and ions to the cathode surface. Concerning tin plating solutions (etch re- sist), metal deposit uniformity is critical. is is especially critical on the pads and the knee of the via. in deposits oen occur in these areas on the circuit board. As a consequence of thin plating, the etching process's opportunity to cut through the tin is easily realized. is then may lead to the etching of the plated copper. is issue is mitigated with best practice agi- tation. While air and eductor agitation are con- traindicated for electrolytic tin plating, me- chanical agitation is a must. Tin plating best practice is to set up through-hole mechanical agitation. is action ensures optimal deliv- ery of process chemistry to the surface of the board and through the vias. Summary Certainly, most operators and engineers worry about controlling the wet chemistry of the printed circuit board fabrication's various processes. Yet, they are oen surprised and disappointed that the finished product's qual- ity is not meeting stringent requirements and key workmanship standards. Further exami- nation will find that other aspects of the pro- cess oen overlooked were not controlled and maintained. us, it only makes sense that in addition to wet chemistry, other non-chemi- cal factors be monitored and controlled. ese include rinsing, filtration, agitation, and tem- perature controls. Ignore these best practices at one's peril. PCB007 Michael Carano is VP of tech- nology and business develop- ment for RBP Chemical Tech- nology. He is also a long-time PCB007 Magazine columnist. To read Mike's columns or contact him, click here.