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18 PCB007 MAGAZINE I NOVEMBER 2023 Copper plating surface distribution with the latest cell designs can achieve down to 2–5% surface thickness variation, with similar result for the etch-down. ese surface tolerances are better than anything that is possible from mechanical planarization of buttons, thereby improving yield and SI performance. 3. Elastic and Noise Steps Elastic and noise operations impart very little variation to the registration process but must still be considered when specifying e q u i p m e n t . Co n s ider at ions s uch as grip- per/suction c u p p l a c e m e n t to avoid fidu- cial damage, dry film coverage areas, and fix- ture-contact locations can make a registration system inoperable if not accounted for. Hack: Edge alignment and machining Edge alignment is a topic oen given insufficient atten- tion in most fabs. Measurement of the edge location on CCL by cam- era, followed by drilling of imaging fiducials/2D codes, will oen save a few millimeters of panel area. More importantly, however, it decreases the flash rout compensation aer lamina- tion. is is particularly important on sequen- tial lamination products, where cutting back too much each time can lead to the need for carrying extra inventory of different dry film sizes, or even damaging tooling fiducials. Fail- ure to cut back enough carries the risk of par- ticle generation due to glass fibers and resin debris, since the edge encounters multiple de- smear operations leading to debris formation if not cut back sufficiently (typically causing a higher incidence of plating nodules and imag- ing defects on SBU product if not managed). e bill of materials can also be broken down into three general categories: 1. Stackup. 2. Tooling frame and sub-frame layout plus thieving strategy. 3. Manufacturing compensation factors. Stackup e product stackup selection process is at the intersection of customer design require- ments and the fab manufacturing experience. Choosing constructions based upon model confidence factors and quality history is becom- ing the norm worldwide. Oen, compromises must be made to achieve the customer require- ments. One of the biggest problems we see in stackup selection arises from excessive focus on core selection, instead of force vector analysis. Some cores work very well i n s o m e s t a c k - u p s , w h e r e a s t h e y p e r f o r m p o o r l y i n others. It all comes down to a d ja c e n t c o r e / sub inf luence a s w e l l a s B - s t a g e selection; this interpo- lation is a blind spot that is oen missing in most industry models. Tooling Frame and Sub-frame Layout Plus Thieving Strategy e design of the tooling frame is one of the most important elements to consider when developing a top-notch registration system. Historically, the tooling frame design was the result of an evolutionary process as equipment fiducial requirements changed only when equipment was replaced. Because of the cost of re-tooling legacy products, frame-tooling is oen not updated even when there are much better coupons that could be used with the new, more capable equipment. One of the biggest problems we see in stackup selection arises from excessive focus on core selection...