Design007 Magazine


Issue link:

Contents of this Issue


Page 17 of 89

18 DESIGN007 MAGAZINE I OCTOBER 2018 In this month's column, I will write about what makes a great incoming dataset for PCB fabrication. Drawings and README Files The overall part thickness should be expressed as the desired thickness measured between two points, including tolerances. For example: • 0.062" ±10% metal-to-metal including surface finish This description tells us the part will be 0.062" nominal with an allowed vari- ance of ±10% mea- sured over the fin- ished plated metal and surface fin- ish. If the draw- ing or README file merely states 0.062", the fabri- cator must estab- lish whether or not this is a max- imum thickness or if a tolerance is associated with it. The note also says nothing about what dis- tance 0.062" refers to. Is it 0.062" glass-to-glass over the material, or is it metal-to-metal? Does this include plate-up and surface fin- ish, or is it an overall dielectric with a toler- ance, such as ±10%? Thickness callouts for single-sided or dou- ble-sided orders are even more critical. As a fabricator, we can control the thickness of the multilayer by using different combinations of prepregs/cores. If a customer calls out a sin- gle-sided or double-sided job as 0.008", is this the core dielectric or an overall dielectric? If 0.008" represents the core dielectric callout on a 2-ounce finished part, the final thickness would be closer to 0.013". If the callout for 0.008" pertains to the overall fin- ished thickness, we would need to start at a 0.004" core to finish at approx- imately 0.009" after plate, surface finish, and mask. Again, notes about thick- ness should ide- ally describe what the overall thickness is to be and the points from which they should be mea- sured. Another exam- ple of drawing call- outs that can require clarification is copper callouts. If the drawing or README file expresses the copper merely as 2-ounce copper, this leaves the fabricator with more ques- Getting on the Same Page: A Data Story The Bare (Board) Truth Feature Column by Mark Thompson, CID+, PROTOTRON CIRCUITS

Articles in this issue

Archives of this issue

view archives of Design007 Magazine - Design007-Oct2018