Practical Tips for specifying PTH for Press-Fit applications

  1. mhoulroyd
    mhoulroyd
    Hi PCB Design,
    I hope this will help any engineer out there who needs to mount socket devices
    onto thick PCBs. When working with very thick PCBs (ie: .125"+) and PCBs with heavy internal layers, soldering may become very difficult. Some customers when noticing that solder only flowed half way up their PTH, attempt to fill in the hole from the topside. This can only lead to bad things (ie: lifted pads and traces). There are some alternative solutions:

    If you can find sockets with a "compliant" tail technology, such as eye-of-needle, this eliminates the need to solder the socket. Eye-of-needle termination is excellent because it allows you to manufacture PCBs to standard finish hole tolerances (saving you money)

    But if on the occasion, you need to work with a solid pin geometry, such as .025" square post, here are some guidelines which may help you.
    1. Specify a starting drill size, slightly larger (about .001") than the press-fit feature.
    (specifying the starting drill size is key, to allow the PCB house to use any drill size may result in holes being way too small or large, possibly causing delamination or having the part fall out)
    A new drill will typically have a tolerance of +0/-.0008", this will slightly close up the hole
    (that is why you're making the starting hole about .001" larger than the press-fit feature)

    2. Specify a finish hole size that will give you approximately .002" of interference fit. If you're using a hard gold finish, the finish hole size might need to be tweaked, if the press-fit forces are too high.

    If you find you need help with the concept of press-fit retention, please let me know and I'll be happy to help you. Regards, Marty

    I started my electronics career in 1980, I worked for a company called Algorex, it was a pioneer in PCB CAD design. After we manually captured signal nets on Fortran paper, we submitted our capture lists to a keypunch department to generate keypunch cards, to be fed to our million dollar mainframe computer LOL (which probably had the power of a C64).
Results 1 to 1 of 1