Issue link: https://iconnect007.uberflip.com/i/1305670
80 SMT007 MAGAZINE I NOVEMBER 2020 You can ask the supplier to check the types of packages and their pitch being used in the products they are currently building. Here are some examples, but the basic idea is to know the capability of the supplier to handle the larg- est and smallest I/O counts and lowest pitch to make sure types of components you have in your products are being built by the supplier: • Types of through-hole components being used • Smallest components (0402, 0201, and 1005) • Resistor networks with fine-pitch pads (0.4-mm pitch) • BTCs, such as QFN, DFN, LGA • QFP with 0.4-mm and 0.3-mm pitches • CSP/BGA with 0.5-mm pitch • CSP/BGA/fine-pitch with lower than 0.5-mm pitch • Maximum BGA I/O count • Package-on-package (PoP) • Others (please list) The types of packages and their pitches play a key role in the level of defects. For exam- ple, as I have discussed in my previous col- umns, here is a brief summary of defects you can expect for different types of packages: • Plated through-hole (PTH): 4,000 PPM • Gull-wing: 1,400 PPM • Chips, BGA, J-lead: Around 600 PPM • Average of all types: 1,079 PPM What is noteworthy in this study is that through-hole components cause the highest level of defects. It should not be a surprise since the most common process for soldering through-hole components is wave soldering, which has too many variables to control. Since through-hole is not going away for some time to come, even though their number has dwin- dled drastically, you or your supplier may want to consider automated selective soldering for PTH to reduce PTH defects. In the same study, the author found that the type of lead and its pitch plays an important role in defects: • 16-mil pitch (0.4 mm): 13,088 PPM • 20-mil pitch (0.5 mm): 1,878 PPM • 25-mil pitch: 950 PPM • 50-mil pitch: 650 PPM When the pitches get below 0.5 mm, the defect level really skyrockets. If you cannot avoid 0.4-mm pitch, you really need to focus on the manufacturing capability of your sup- plier to successfully deal with fragile leads of ultrafine-pitch packages. Put another way, if your product contains pitches below 0.5 mm, there are very few companies that can build them with good quality on a consistent basis. Thus, your audit process must be a lot more rigorous if you need to assemble ultrafine- pitch components. There is no such thing as a perfect PCB sur- face finish. All surface finishes—such as HASL, OSP, ENIG, immersion silver, and immersion tin—have their pros and cons. In most cases, the assembler does not make their own PCBs; they order them from a PCB supplier. An assembler who is a turnkey supplier is respon- sible for selecting their own PCB supplier. On the other hand, if you specify the surface fin- ish, you should ask the same questions from the PCB supplier. Here are four examples of questions that should be asked about different surface fin- ishes being used on your product: 1. ENIG surface finish: Did you ever have black pad incidence? How was it resolved? Very few suppliers are willing to admit the problem, but black pad is a potential problem with ENIG, and you should ask about it. 2. Immersion silver: Have you ever had champagne micro-void incidence? If so, how was that resolved? 3. OSP: Have you ever had BGA ball drop incidence or any issues with via fill during wave soldering of mixed assembly? Did you have to use a more active flux or nitrogen to achieve 100% via fill? Even though only 75% via fill is required, if you always get that 75% minimum, it is not acceptable quality. 4. HASL: Since the inherent problem with this finish is an uneven surface finish, it is