Issue link: https://iconnect007.uberflip.com/i/1011746
76 PCB007 MAGAZINE I AUGUST 2018 Preventive mainte- nance within a manufac- turing facility is extremely crucial to quality and ul- timately, for product reli- ability. This is an area that can be often overlooked and difficult to schedule due to day-to day opera- tions and constant work flow. Along with employ- ees, equipment is the heartbeat of the compa- ny. Imagine if you nev- er maintained your etch- er and half the conveyor rollers are bound up with crystalized ammonia and you're running an imped- ance control job. Most likely the impedance control traces will be un- der-etched causing impedance readings either out of spec, or on the edge of their tolerance. There are 35 different process steps when fab- ricating a simple two-layer PCB; if no PMs were performed at those process steps, I think it's obvious what the result would be. These three examples are just a microcosm of things to be checked, monitored, and ana- lyzed during and after the manufacturing pro- cess of electronic parts. Other process controls such as employee training, calibrations, and inventory control all pertain to product reli- ability in one way or another. When choosing a PCB manufacturer or PCB assembler, be sure it's the right fit for your company. I have found that a company's web page says a lot about the nature their business. Take the time to ask questions, maybe even visit or audit their fa- cilities, don't just rely on the lowest price, as price can certainly be a contributor to end- product reliability. PCB007 Sam Sangani is president of PNC Inc. step to ensure the repeatability from the rout- ing step. An example of part verification during the assembly process step of pick and place would require an FAI. The FAI will indicate wheth- er parts are missing, skewed, misplaced, prop- er polarity, correct rotations, etc. This is a very critical step that needs attention prior to reflow to eliminate rework. Rework can be a major contributor to end-product reliability. When it comes to PCB testing, be sure that your PCB manufacturer is 100% electrical test- ing your parts. Standard continuity testing is typically 100 V, 50 mA, 10 ohms (low resis- tance), and 10 megaohms (high resistance). The testing should also be documented and supplied with your PCBs as verification. Assembly testing can be performed at var- ious levels depending on your requirements. Full functional burn-in testing is obviously the best method for reliability purposes, but again, depending on the design, the assembled part may only require some voltage input/output testing. Partial functional tests may be suffi- cient for reliability based on the function of the design. For mass production assembly runs, flying probe tests are a cost-effective and high- ly reliable means of testing for end-product re- liability. Figure 3: Sample defect analysis.