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70 SMT007 MAGAZINE I APRIL 2021 No matter how long you have been in the SMT industry, there is always something new to learn because SMT is constantly evolving even though it is a mature technology. For example, we have been manufacturing SMT products in high volume for almost four decades, but less than 10% of companies have a first pass yield of more than 90%. In other words, 90% of compa- nies are conducting too much rework. In some of my previous columns, I have gone into detail on the types of defects that are predominant. ere are many reasons we worry about defects, but the key reasons are increased cost and reduced reliability. ese defects must be reworked so that you can meet the delivery requirement without too much delay. Even if you can minimize the delay in shipping the final product, if you must do rework, there is no way to prevent reduc- tion in reliability. Why? Each time you heat the solder joint, you increase the thickness of the intermetallic layer. e intermetallic com- pound (IMC) is necessary to achieve a reliable bond between the component and board, but too much IMC is not good. It is brittle and if it is too thick you have potentially early fail- ures in the field. ere is nothing worse than field returns for any company since they are not only expensive to repair, but they can also adversely impact a company's reputation. With the advent of fine- and ultra-fine-pitch, high-pin-count BGAs, 0402, 0201 and 01005 resistors and capacitors, as well as the wide- spread use of no-clean flux, yield problems are Major Drivers for Improving Yield and Reducing Cost SMT Solver by Ray Prasad, RAY PRASAD CONSULTANCY GROUP

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