Issue link: https://iconnect007.uberflip.com/i/1359517
108 DESIGN007 MAGAZINE I APRIL 2021 ensure that the customer gets the product that is best suited to the application. e following are discussions on matters of high importance to achieving first-pass success in securing quality flexible circuits from a flex circuit vendor. It is important to provide some informa- tion about the operational requirements for the flex circuit, especially if the circuit is to be used in a dynamic flexing application, such as for a disk drive read/write head assembly. e reason for this is the circuit vendor needs to provide a plan for proper layout strategy for manufacturing; a plan which accounts for the grain direction of the copper foil during the manufacturing process. is is because there is a measurable difference in terms of flexing per- formance between the machine and transverse directions of the copper foil. Fabrication Specification Details Aer the basic circuit design layout is com- pleted, the next most important piece of infor- mation required is the fabrication specifica- tion. is document communicates to the fab- ricator all the pertinent details for the physical construction of the circuit and what is needed and expected in the final product. If this infor- mation is incomplete or inaccurate, or if a cus- tomer has requirements that cannot be reason- ably met by a competent manufacturer, time will be unnecessarily lost, at a cost to both the customer and the vendor. For this reason, it is vitally important that the fabrication specifica- tions are checked and rechecked before put- ting them out for bid. In the sage words of the master carpenter, "Measure twice, cut once." Manufacturing Tolerances Manufacturing system operators need not only the dimensions of the part they are to manufacture, but also the tolerance for the important features of the product. With flex- ible circuits, this is something that must be done with thought, care, and consideration of the realities of flexible circuit materials. With some features, design tolerances may be critical for the performance, fit, or fur- ther processing of the product (line widths, spaces, hole sizes, physical separation of fea- tures, positional accuracy, etc.). In these cases, the manufacturer can oen employ methods to deal with the requirement on a localized basis. In the case of other features, the toler- ance may be less critical, significantly less criti- cal, or even non-critical. An important thing to keep in mind is that flexible materials are not as dimensionally stable as rigid materials, and while local features may be held in tight toler- ance relative to each other, features from end to end may be less predictable. Given that flex- ible circuits are normally installed in some 3D form aer assembly, the tight tolerances on planar measurements are oen not necessary. If there are questions about a tolerance callout, the designer should contact the manufacturing engineer. It is always best to solve the problem before it becomes a problem. Unclear Layer Designation (Rigid or Flex) e purpose of a product specification is to provide clear, unambiguous instructions on the product's construction. In the case of a multilayer circuit design, this is vitally impor- tant. e relationship of internal circuit layers relative to one another has become increas- ingly important in not only assuring that cor- rect interconnections are being made, but also in product performance, especially with con- If there are questions about a tolerance callout, the designer should contact the manufacturing engineer. It is always best to solve the problem before it becomes a problem.