Issue link: https://iconnect007.uberflip.com/i/1535414
MAY 2025 I PCB007 MAGAZINE 79 With rinse water cleanliness, don't underes- timate the potential for cross-contamination on circuit boards that will lead to failures such as electromigration or simply less reliable plat- ing and surface finishing. Insufficient rinsing aer solderable finishes will lead to assembly failures, and the potential for field failures such as corrosion. A low-cost investment in con- ductivity probes will monitor the effectiveness of the rinsing and minimize excess water usage. Finally, monitoring the pH of key processes such as resist development will minimize sit- uations where incomplete development and/ or resist residues remain within tight lines and spaces. e concern here is opens and shorts. Test Vehicles/Thermal Reliability Methods Designing test vehicles to mimic circuit board designs is necessary to ensure prod- uct reliability. en employing one or more of the IPC test methods below provides further opportunity to improve processes. IPC published a test method designed to screen blind vias aer boards have been manufactured. e convection reflow simulation test method (IPC-TM-650 2.6.27B) exposes the PWB to the highest temperature extremes it will encounter during reflow assembly. Unlike other IPC test methods, IPC-TM-650 2.6.27B uses continuous resistance monitoring of daisy chains during con- vection reflow to detect failures in real time. e acceptance criterion is a less than 5% increase in resistance using the first cycle's peak temperature resistance as the reference value. Complement convection resistance test- ing with air-to-air thermal shock testing (IPC- TM-650 2.6.7.2C). Identical test coupons (IPC- 2221B D coupon) and test systems are suitable for these methodologies. e 5% acceptance criterion remains, despite measuring resistance only once per cycle at the high-temperature extreme. e test conditions are limited by the material parameters (Tg minus 10°C) and the reflow temperature (25°C below peak). Figure 2 (IPC-TM-650 2.6.27) shows the D-coupon setup used for reliability testing. Quality is everyone's business and job. Take no shortcuts. PCB007 Michael Carano brings over 40 years of electronics industry experi- ence with special expertise in man- ufacturing, performance chemicals, metals, semiconductors, medical devices, and advanced packaging. To read past columns, click here. Figure 2: D-coupon for OM test.