Issue link: https://iconnect007.uberflip.com/i/1525368
38 PCB007 MAGAZINE I AUGUST 2024 of those things suffer, the blame game begins. ings go wrong. Stuff happens. ough true, that is not the attitude to have when yields go south, and a process may be out of control. e first thing to know is what's out of control? Is it the pH of the resist developer solution, or the specific gravity of the alkaline etchant? Are these special or common causes? A special cause indicates that something in the related processes caused the change. In other words, there is an assignable cause. Where is the pro- cess control management plan, and where is it listed for all to see? What if there was no signifi- cant change? en one does not have a specific assignable cause. Engineers should not assume this is a one-off, and the problem has disap- peared. ere are multiple variables within the printed circuit board manufacturing process. at is a fact. Having a deep understanding of these possible variables and their ultimate effect on quality is the cornerstone of process control and management. Wet Process Control: Not Only About the Chemistry Now I will explore some process control ideas that are easy and cost-effective to imple- ment. ese include conductivity probes, online real-time analysis of electroplating solu- tions, and simple specific gravity measure- ments. I strongly suggest that operators and engi- neers monitor all aspects of the processes for each unit operation. is includes walk- ing the line, taking measurements, recogniz- ing what is not in control, and getting it back within range. Quality and yields should come first. SPC charts that dot the walls of the com- pany's laboratory give the impression that key unit operations in manufacturing are in con- trol. at is not always accurate. For example, several processes may be set up for automated analysis and replenishment of critical chemical additives. However, this oen only covers the basic additives in the electroplating or electro- less plating processes (copper concentration, acid levels, etc.). What about the organic addi- tives (leveling agents, throwing power enhanc- ers, and stabilizers) that have a profound effect on the overall quality and reliability of the plated deposit? How do you know with any confidence that these critical additives (special additives that influence ductility, grain struc- ture, and resistance to thermal excursions) are in the proper range? Organic Addition Agent Control in Electroplating I suggest utilizing a real-time analyzer (Fig- ure 1). is unit provides real-time and accu- rate analysis of the key organic addition agents in the electrolytic copper plating solutions. It is understood that the organic addition agents (grain refiners, leveling agents, and high current density suppressing additives) enhance the uniformity, leveling, and reliabil- ity of the plated copper deposit. Properties of the deposit, such as ductility (elongation) and tensile strength, must be in tight control to prevent failures in the plated through-hole and blind vias due to thermal and mechanical excursions. Figure 2 shows the result of low additive con- centration in the electrolytic copper plating solution. While many rely on the old-fashioned Hull Cell method to control organic addition Figure 1: Real-time analysis of copper plating solutions. (Source: Technic, Inc.)