SMT007 Magazine


Issue link:

Contents of this Issue


Page 73 of 96

74 SMT Magazine • February 2014 by Zulki Khan NEXlogIC TEChNologIES INC. ZuLKI'S PCb NuGGeTS ColUMN uncovering assembly Problems of High-Speed PCbs High-speed PCBs have become much more common during the past five years. However, special challenges arise due to unanticipated high-speed issues. Some relate to manufactur- ing or processes, while others are pure compo- nent- or fabrication-based. In particular, highly complex, highly integrated components like FPGAs need close scrutiny. Also, it's important to note that PCBs may use mixed materials like Rogers and FR-4 cores in order to incorporate those high speeds. The mixed-material board may need pre- preg special processing and temperature treat- ment compared to conventional FR-4 boards. In such cases, extra care must be applied to watch for certain manufacturing aspects. For example, high-speed boards might pass at cer- tain lower spectrum speeds, but begin failing at certain other higher speeds. However, when it comes to regular investigation, those same boards might pass all the run-of-the-mill tests like flying probe, functional tests and ground- to-power short tests. It becomes worrisome when these boards fail at certain high-speed level bands. Inves- tigation as to the reason(s) why they fail in- clude checking out the process and dissecting it step-by-step and scrubbing the bill of materials (BOM) all the way from A–Z to make sure there are no issues during verification testing. The high-speed board may be perfect when it comes to BGA assembly. All the balls properly collapse; all the thermal profiles are accurately determined and performed. All soak tempera- tures, pre-heat, soak and cool-off periods fall within manufacturer limits and ranges. A sam-

Articles in this issue

Archives of this issue

view archives of SMT007 Magazine - SMT-Feb2014