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94 SMT007 MAGAZINE I SEPTEMBER 2020 facturing capability, I am only talking about assessing or auditing, if you will—the capabil- ity of a company to produce consistent qual- ity over time. In this column, I will provide an overview of the audit process. In future col- umns, I will delve into the details of questions that should be asked to assess the major areas, such as technology, manufacturing, and the quality of the company being audited. Audit Process: An Overview We need to begin with defining the complex- ity of the product that needs to be built. Not everyone has the expertise to build all types of products, especially complex mixed-assembly boards. Also, they may not have skilled and experienced technical personnel. Even the best companies will find it challenging if the prod- uct requires the assembly of packages, such as fine-pitch, BGA, BTC, 0402, 0201, or 01005 discrete devices—especially when that board also has legacy components, such as J lead, gull wing, and even through-hole components. Add to this lead-free BGAs in a tin-lead pro- cess, which is very common in products for military applications. Keeping the complexity of the product in mind, the first thing to do before an audit is to prepare a detailed questionnaire for the audit. The questions should be targeted to assess not only the manufacturing capability for tin-lead and lead-free products but also the basic SMT infrastructure of the company, which is essen- tial in building products with consistent qual- ity over time. The answers to these questions will supplement the findings of the audit dur- ing the visit. The objective of the questionnaire is also to give the company being audited a heads up as to what you may be looking for during your visit. Some questions may be considered confi- dential or not applicable, and the company may choose not to answer them. You can draw your own conclusions on whether those ques- tions are confidential or not applicable. If possible, the company should return the completed questionnaire to the auditor a few days before the site visit. Along with the com- pleted questionnaire, it may be appropriate to ask for the following documents to review before the visit to make the on-site visit very productive, especially when you have limited time for the audit: 1. Company-specific design for manufac- turing (DFM) used to build your prod- ucts. DFM means different things to dif- ferent people (I will explore the details in the next two columns), but for now, we want to know the rules and guidelines in DFM for things such as component selec- tion criteria, paneling considerations, fidu- cial requirements, land pattern design, sol- der mask consideration, via hole location, design for test, and anything unique to your design. 2. Company-specific manufacturing process document(s), such as adhesive and paste application, pick-and-place, reflow, wave, cleaning, repair, etc., that are used to build your products. These documents are not dependent on the types of equipment being used in the line. They are essen- tially a recipe the company uses to build the product. An example would be targets for peak temperature and TAL, no matter which oven is being used. 3. Equipment operating procedures. This is equipment specific document. The objec- tive of this document is to ensure all oper- ators use the same procedure when oper- ating the machines on the line. 4. Handling and storage procedure for mois- ture-sensitive components. This becomes even more critical for lead-free. Very few companies have good control on this issue. Not everyone has the expertise to build all types of products, especially complex mixed- assembly boards.

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