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42 DESIGN007 MAGAZINE I NOVEMBER 2020 zation and electroless processes at both. We are making every effort we can to reduce the effect of uncontrolled variables but will try to capture that information and those side effects of shop-to-shop differences. The structures we selected resulted in 17 dif- ferent IPC-D structured coupons. Comparing direct metallization to electroless, that doubles. I will touch on reflow simulation temperatures later. There has been some discussion, and our test labs were very helpful in working through this. We are concentrating exclusively on the weak interface; we are not worrying about the various through-holes that are in the structure by necessity. Even more traditional microvia failures (cracks or voids in microvia sidewall, for example) are outside the scope of this study. We intend to force the failure of the weak interface of the microvias by concentrating on the reflow simulation with the fabricator shops or test labs. Each test lab will get 102 samples of D-coupons from each of the two fabricator shops. One of the variables will be microvia forma- tion. And that is one of the differences between these two shops. Their microvia formation method: one is mechanically drilled, and • Reflow simulation temperature (eutectic, 230 °C, vs. lead-free, 260 °C; 10 reps) • "Test Lab A" vs. "Test Lab B" • Microvia formation method (mechanically drilled vs. laser-ablated, such as UV/CO 2 /UV) • Metallization (direct metallization vs. electroless copper) • Note: Laminate material is not a variable in Phase 1 Some of the variables will be examined. Those of you who have been around the industry for a long time and have tried to do comparative studies of a particular problem or issue recognize that with the best of intentions and the most stringent controls on processes, process consistency and trying to match pro- cesses between two operations, is quite often the biggest and most statistically significant variable about who built the boards. The two participating fabricators were selected in part because of the common pro- cesses they had and our ability to coordinate their efforts with back and forth shuttles. We have gracious technical support from chemical suppliers that supply the same direct metalli- Figure 1: Test vehicle article showing stackup, materials, constructions, and thicknesses. Layer Min Max Thickness Stackup Picture Family Description Type (Inch) TopLayer L1 / L12 DK / DF 0.00 / 0.0000 POWER GROUND-COPPER FOIL 4.02 / 0.0210 SIGNAL – COPPER 4.02 / 0.0210 SIGNAL – COPPER 3.74 / 0.0210 SIGNAL – COPPER 3.74 / 0.0210 SIGNAL 4.28 / 0.0210 SIGNAL 3.90 / 0.0210 SIGNAL 4.28 / 0.0210 SIGNAL 3.74 / 0.0210 SIGNAL - COPPER SIGNAL – COPPER 4.02 / 0.0210 SIGNAL – COPPER 4.02 / 0.0210 POWER_GROUND- COPPER FOIL 0.00 / 0.0000 SM1 L1 L2 L3 L4 L5 L6 L7 L8 L9 L10 L11 L12 SM2 0.00042 0.00273 0.00162 0.00273 0.00162 0.00330 0.00162 0.00412 0.00060 0.00500 0.00060 0.00504 0.00060 0.00500 0.00060 0.00412 0.00162 0.00330 0.00162 0.00273 0.00162 0.00273 0.00042 TAIYO HFX Copper Foil 370HR Copper Core 370HR Copper Core 370HR 370HR Copper Core 370HR 370HR Copper Core 370HR Copper Core 370HR 370HR 370HR Copper Core 370HR Copper Core 370HR 370HR Copper Core 370HR 370HR Copper Core 370HR Copper Core 370HR Copper Core TAIYO HFX .375 2113-59% .375 + 0.0007 2113-59% .375 + 0.0007 106-76% 106-76% .375 + 0.0007 106-76% 106-76% .5 0.0080 (1-7628) .5 1080-65% 1080-65% 1080-65% .5 0.0080 (1-7628) .5 106-76% 106-76% .375 + 0.0007 106-76% 106-76% .375 + 0.0007 2113-59% .375 + 0.0007 2113-59% .375 19 29 23 27 34 24 26 23 33 28 31 20 14 21 20 22 18 12 18 17 11 15 21 12 27 11 10 6 24 7 8 9 13 14 15 16 23 26 22 16 13 4 3 1 17 20 30 32 35 25 25 21 12 29 5 2 19 36 26 24 25