Issue link: https://iconnect007.uberflip.com/i/898297
22 The PCB Magazine • November 2017 Such devices from two to twenty heads should offer fabricators the assurance of proper and re- liable microvias. AOI for Tiny Blind Vias It seems possible, in today's age of solid- state laser diodes and sensitive multi-wave- length imaging chips, that an AOI machine can be created that can scan newly created micro- vias for many of the defects shown in Figure 5. We have LED bar printers with the same res- olution (300 dpi) as laser printers. The wave- lengths can be adjusted to allow the detection of resins or epoxies remaining on the copper at the bottom of these tiny vias. Our sensor and camera technology is superb, along with tre- mendous computing capability, such that cre- ating a piece of equipment for the inspection of microvias a reality. Bare-Board/ICT Solutions for HDI Once these challenges have been over- come, how will we test the resulting assembly? Not everyone has the time or space to imple- ment boundary scan or "built-in-self-test." Oth- er cost-effective solutions need to be found to make sure we have a functioning product. In 2011, I completed a tour of European and Chinese PWB shops. The amount of HDI sub- strates in prototype and on a production ramp was heartening. I also had an opportunity to talk with several large semiconductor packaging firms about their use of HDI organic packages. The semiconductor companies are planning to fill the demand for finer pitch BGAs and chip scale packages, all of which require HDI sub- strates. This is good news for all those fabrica- tors who have invested in HDI production pro- cesses. Only one problem (well, one of many, Assembly Sub-panel test coupons HATS Panel test vehicle PCQR 2 CAF TV Solder joint TV TV TV TV TV Fabrication Panel test coupons Via Reliability CAF Reliability Layer registration stacking stripes First / last hole QC code ASSY Barcode C C V v 7 8 123456 7 8 123456 C C V v 7 8 123456 Production Panel Figure 6: Small process test coupons used on fabrication panels and assembly sub-panels providing traceability and reliability continuity. 35 YEARS OF HDI FABRICATION PROCESSES AND OBSTACLES FOR IMPLEMENTATION