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FEBRUARY 2018 I DESIGN007 MAGAZINE 79 Copper Weight Copper weight can be further categorized into outer layer copper weight and inner layer copper weight that should be respectively cal- culated and emphasized. Since copper weight is directly associated with board thickness, it has to be carefully measured. Minimum Tracing/Spacing Tracing/spacing is a delicate element of a manufacturer's capabilities, since it is associ- ated with board size and density level. PCB designers should be fully aware of minimum tracing/spacing requirements so that they can optimize their PCB design files. Solder Mask Solder mask is more than just a variety of colors. Advanced solder mask, peelable solder mask, and carbon mask can be used to evalu- ate your partner's capabilities. Surface Finish Various surface finishes are selected for advantages and disadvantages on perfor- mance, cost and applications. Plus, RoHS com- patibility matters for products that are required to be environmental-friendly. Other Items Other items are primarily associated with advanced capabilities such as blind/buried vias, via-in-pad, gold fingers, edge plating, countersink/counterbore hole, etc. As far as via or hole parameters are concerned, most atten- tion should be paid to via diameter because it straightly reflects whether manufacturer's capability can meet your design demands. Assembly: When qualifying a company's PCB assem- bly operations, the following items should be emphasized: Quality Grade As with PCB fabrication, for advanced, high- quality assembly, the OEM should select an assembly provider that offers advanced capa- bilities. Assembly Types Two leading types of assembly are available: plated through-hole (PTH) and surface mount technology (SMT). In complicated conditions, both technologies are often simultaneously required. If assembly sequence is arranged improperly or an inappropriate soldering tem- perature is set, defects or failure may result. Thus, your contract assembler should be able to maintain high-level assembly capability. Assembly Accuracy Assembly accuracy is another key element evaluating assembler's manufacturing capabil- ities. Since miniaturization has become one of the key trends in electronics, assembly density and accuracy start playing an increasingly sig- nificant role that should be in your first batch of considerations. The facility's minimum component size, 01005, for example, should be known and confirmed in advance. Component Packages Various types of component packages are available, but not all assemblers can deal with all component packages, so it's neces- sary to get assured that your required compo- nent packages like QFN, BGA, and CSP can be assembled by your potential partner. Inspection and Test To be aware that your products have been manufactured in accordance with original design, inspection and test are vital. For PCB fabrication test, custom electrical test such as bed of nails or flying probe is often required. But for PCB assembly test, however, AOI or AXI is required. During assembly process, AOI usu- ally comes in two formats: online and offline. For high-quality NPI, the OEM should know whether both types are available. During assembly process, AOI usually comes in two formats: online and offline.

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