Issue link: https://iconnect007.uberflip.com/i/1339822
76 PCB007 MAGAZINE I FEBRUARY 2021 ere are multiple variations within the print- ed 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 con- trol and management. is understanding be- comes the basis for complex troubleshooting activities. Approaches to Process Control I strongly suggest that operators and engi- neers monitor all aspects of the processes for each unit operation. is includes walking the line, taking measurements, recognizing what is not in control (and getting it back within range). Quality and yields must come first— not pushing out production and cutting pro- cess costs! Indeed, SPC charts are oen seen dotting the walls of the company's laboratory, theoretically giving the impression that crucial unit operations within the manufacturing facil- ity are in control. at is not always accurate. For example, several processes can be set up for automated analysis and replenishment of critical chemical additives. However, this oen only covers the basic additives in the electro- plating or electroless plating processes (copper concentration, acid levels, etc.). What about the organic additives (leveling agents, throw- ing power enhancers, stabilizers) that pro- foundly affect the overall quality and reliabil- ity of the plated deposit? How does one know with any confidence that these critical addi- tives (special additives that influence ductili- ty, grain structure, resistance to thermal excur- sions) are in the proper range? e fabricator can rely somewhat on the chemical and material supplier for the analy- sis of key organic additives. In general terms, these critical additives are packaged so that they are replenished as the essential inorgan- ic additives are added. Yet, TGW—there is po- tential for additive decomposition and the po- tential of over-adding these materials. is is precisely why different approaches to process control are needed. is means that additional analytical methods, coupled with quantitative measurements of rinse water cleanliness and temperature, are critical to success, along with the basics described above. In addition, oper- ators should regularly inspect nozzles in vari- ous spray modules for wear and tear, then re- place those nozzles as needed. Finally, meth- ods to prevent the drag-in of harmful chemi- cals and enhanced filtration of all solutions are just several of the best practices that must be implemented. Figure 1 shows the significant hole wall roughness. Analysis of this situation told the tale of too many hits from the drill bits. e fabricator looking to cut costs increased the hit rate from the recommended 2,000–2,500 hits to 4,500–5,000 hits, with deleterious con- sequences! Best practices were not being fol- lowed here. When best practice procedures were implemented—all drill bits were limit- ed to 1,700–2,000 hits, resharpened once, and then discarded aer another 1,500 hits—the drilled quality drastically improved, as did the subsequent plating quality (Figure 2). Benchmarking Best Practices e above example aside, let's review what this author considers critical performance en- hancers that oen are not considered impor- tant by many fabricators. is is only a partial Figure 1: Extreme rough hole wall due to poor drilling practices.