PDF of this tutorialThe PWB fabrication experiments will include a process parameter study of drilling, adhesion, stability, and press guidelines. Additionally, sheet size, core/prepreg, and thickness availability will affect the system usability, as these may limit the application of the performance laminates.
At the final system level, compatibility with connector and device termination must be considered. For daughtercards and active motherboards, the PCBs will be subjected to reflow temperatures. A reliability study must be completed on the new laminates. Hybrid boards where new materials will be mixed with FR–4 layers will need to be checked for delamination and barrel cracking due to the difference in temperature coefficients of expansion (TCEs). Currently, the predominant backplane connector is a press-fit compliant pin termination, as a result of difficulty in uniformly soldering the large thermal mass of today’s backplanes and the proven reliability of this interface. Additionally, it is preferred because of the ability to repair a single damaged pin on a large, populated board. Experiments show that, due to the differences in adhesion and laminate modulus, the compliant pin/board interface must be altered from the FR–4 recipe for some advanced laminates (see Figure 6). A full test sequence has been developed to ensure the long-term reliability of the gastight pin/barrel joint.
Figure 6. Future Work
