Issue link: https://iconnect007.uberflip.com/i/1507822
52 PCB007 MAGAZINE I SEPTEMBER 2023 as the vacuum gauges indicated full vacuum. For the 0.004" space panels, it was found that by delaying the panel exposure for 30 seconds aer full vacuum was drawn, it brought their yields back to the 95% range. e extra time allowed the phototool to come into closer con- tact with the resist and prevented leakage from their non-collimated light source from caus- ing shorts across the narrower spaces. Ulti- mately, they upgraded their exposure units to ones with collimated light sources and better and more consistent vacuum draw- downs to meet the specifica- tions of the then high-tech products. By today's standards, this is a relatively crude example, but it does show that some attention to other process steps as well as etching can solve some problems involved with high density circuit pro- duction. A more recent example is provided by two companies I assisted with about two years ago. Both companies were making high-den- sity flex circuits using a reel-to-reel process. Company B was consistently outcompet- ing Company A for business and Company A could not understand why. Both companies were long time customers and familiar with each other, so Company A was aware that Company B had a newer model etcher. ey assumed that this was the problem, asked for an audit of their etcher, and for information on the latest advances in etcher technology. Company A's etcher had been purchased in the mid-'90s but had been well maintained and optimized for their production. When I ran and analyzed my test panels, I saw that their etcher performance was on par with the etcher in my lab, which was the same model and vintage as Company B's (circa 2015 or so). I informed the management that I didn't think a new etcher would improve their competitive outlook. is advice was not well received. If not the etcher, what else could it be? e difference was that when Company B decided to get into HDI production (UHDI was still in the future), they took the time to study each process step in the production line, from incoming materials to outgoing packag- ing, and looked at how to optimize each step. In the etching process, they looked in detail at surface prep, types of photoresists, resist application, phototools, resist exposure, developing, and etching. By "in detail," I mean they analyzed such things as roller temperature for dry film lamination, expo- sure times and intensities, developer concentra- tions, etc., to find the most efficient and cost-effective ways to accomplish their goals for high density inter- connects. e research took two to three years to complete but, in the end, they were positioned to succeed in a highly competitive market. Some equipment upgrades were required but, for the most part, all that was needed was to tighten operating procedures and find the best operating parameters for each process. As far as I know, Company A is still looking for that silver bullet in terms of new etcher tech- nology that will make them more competitive. e moral of the story: As circuit features shrink and are squeezed into smaller and smaller spaces, one should focus on optimiz- ing every step in the circuit formation process and not just one small area where you assume the problems exist. PCB007 Don Ball is a process engineer at Chemcut. To read past columns, click here. The research took two to three years to complete but, in the end, they were positioned to succeed in a highly competitive market.