Issue link: https://iconnect007.uberflip.com/i/1305670
82 SMT007 MAGAZINE I NOVEMBER 2020 It is also important to ask about the test strat- egy (ICT, flying probe, functional, etc.) used on the product—especially when you see a large bone pile on the shop floor. A large bone pile is common in companies that do not use ICT and have high defect rates. Technology Questions The types of machines used by a com- pany are important. However, the existence of detailed and formal design and process doc- uments and extensive training programs for operators, technicians, and engineers are the key elements of a strong SMT infrastructure of a company. You should ask about the number of engineers working on manufacturing pro- cess development and on the production floor, and their qualifications. And the questions should be intended to assess their understand- ing of the technology. For example, you should ask about the prop- erties of solder paste (compositions, metal content, particle size range, etc.) to see if they have been selected for a reason: • What is the solder application method (stencil or screen)? • Why was this method chosen? • What is the paste deposit thickness? • Does this thickness requirement change if fine-pitch is used on the same board? • What is the approach (differential stencil thickness versus micro-modification of stencil aperture) for applying the paste on a board with standard surface mount and fine-pitch? • Have they looked into the implications of each approach? • Do they get heel fillet in fine-pitch without getting insufficient fillets in standard components? • What is the reflow soldering method used (vapor phase, infrared, convection, or combinations thereof)? • What are typical thermal profiles on the board surface and at a solder joint? • Do they develop a unique profile for each board? • How and where are the thermocouples attached? • Are they attached on the surface or on the solder joints? • Is the board drilled to attach thermo- couples to the BGA balls on the outer and inner layers? • If not, how do they know if the BGA balls really reflow? • Have the reflow processes been compared for manufacturing yields? In developing a profile, there is an inherent conflict between the type of profile you need for a BGA (shorter soak time) and what you need for BTC (longer soak time). What does the supplier do when both are on the same board, which is a very likely scenario? Devel- oping a reflow profile for electronic assemblies is like trying to figure out the time and temper- ature (bake profile) to bake turkey, chicken, and shrimp for the same length of time at the same temperature in the same oven without undercooking the turkey or overcooking the shrimp. Your questions should focus on assessing the inherent technical capability of personnel to resolve complicated technical issues that they need to deal with all the time in a complicated assembly: • What cleaning method and solvents are used? • How is the cleanliness of product boards monitored? • What sort of repair/rework equipment is used? • What are the thermal profiles for repairing each surface mount device type? To determine whether the company has any experience or plans to develop capabili- ties for newer technologies such as BTC, BGA, and ultrafine-pitch packages (if your prod- uct requires them now or in the future), you should ask detailed questions related to that technology. For example: • Are you planning to achieve toe/side fil- lets in BTCs, and if so, how?