Issue link: https://iconnect007.uberflip.com/i/1509873
OCTOBER 2023 I PCB007 MAGAZINE 47 Figure 1: Representative of PTH reliability test coupons. (a) coupon contains three sets of 1000 PTHs interconnected in series, (b) interconnect stress testing (IST) coupons, (c) highly accelerated thermal shock (HATS) coupon, and (d) process capability, quality, and relative reliability (PCQR2 ) coupon. Adhesion is commonly tested using the peel test described in IPC-TM-650, Method 2.4.28. e simplest version of this test is conducted by scribing the adherent and dividing it into small squares. If the Cu or solder mask pulls off with a piece of tape with strong adhesive, the adhesion is inadequate. More quantitative tests that measure the actual peel strength are per- formed primarily by laminate and solder mask suppliers. Temperature, humidity, bias: ese tests are designed to promote corrosion on the PCB surface and conductive anodic fila- ment growth, either of which can cause insu- lation resistance failures. Surface n insulation tests utilize two interleaved Cu combs with an imposed DC bias across the combs. ese combs may be designed into existing boards or a coupon such as the IPC-B-25 test board (Fig- ure 2) may be used. e measured resistance (ohms) from the comb pattern can be con- verted to surface resistivity (ohms per square) by multiplying the measured resistance by the square count of the pattern. e square count is determined geometrically by measuring the total length of the parallel traces between the anode and cathode and dividing by the separa- tion distance. Special precautions are needed