Issue link: https://iconnect007.uberflip.com/i/1143487
32 PCB007 MAGAZINE I JULY 2019 15 microinches. By comparing the Au thick- ness on the connector pins in Tables 2 and 3, it shows that the Au thickness on some con- nectors is only 1 microinch and is more than 15 microinches on other connectors. The Au thickness measured on the poor-contact NIC/ SSL (Table 4) is also less than 15 microinches. It is thus seen that the probability of poor con- tact is much larger on connectors with 1-mi- croinch Au plating than that on connectors with 15 microinches. Second is the increase in damping plate ar- ea and thickness. In the original system, there were no damping plates on the riser card and NIC/SSL card. Changing the damping materi- al from plastic to more elastic foam material helped to enhance the damping effect of the system to overcome external shock load. The new foam will continue in contact with the riser card with no gap between the foam and riser card. It can prevent the riser card from coming out of connectors under transporta- tion stress. In the current design, the riser card was pressed by one plastic part and the NIC/ SSL card were pressed by foam (Figure 5). The exact thickness of the foam damping plate is based on the following tolerance analysis. The tolerance analysis (TA) conducted on the stack of mechanical parts indicates that there is some tolerance among different me- chanical parts when the top cover is assem- Table 3: Hard gold plating thickness of various interconnect devices. Table 4: Example of plating thickness of press-fit connector. Figure 5: Foam plates added to enhance the damping effect.