Coming Up Short

Figure 1.

Figure 1. Original part’s through-hole pins are not long enough to go through the board and be soldered from the bottom side.

Figure 2.

Figure 2. Cross-section of PCB showing penetration depth of part’s original pins.

Figure 3.

Figure 3. Side view showing new pin length (inset: bottom side view).

In another PCB assembly challenge, the customer’s BoM called for a through-hole header part to be installed on a circuit board, a mixed technology (SMT and PTH) assembly. A problem became immediately apparent with the first PCB that our operators began to assemble; this was a very thick circuit board (12.15mm thick), but the part specified and received did not have terminal pins long enough to protrude all the way through the PCB to other side (bottom side) (Figure 1). Obviously, we needed the pins to penetrate all the way to the bottom side and protrude so that they could be properly soldered using wave or selective soldering techniques.

What to do?

In this instance, a replacement part with pins of sufficient length simply wasn’t available. The easiest solution (although labor-intensive) required manual removal of all the original pins from the part, and their replacement with longer pins of sufficient length, actually, to form good and robust solder joints on the bottom side of the PCB assembly (Figure 3). Once the longer pins were added, it became a simple matter to re-insert the through-hole header part and solder it in place from the bottom. The parts of the pin protruding from the solder joint could then be dealt with the same way as any other soldered through-hole pins.

Roy

rushpcb.com/rushblog/

Package Variants

Cap under connector footprint Here’s another issue we see from time to time involving the old, familiar, 0.1″ pitch headers. Break away header When initially laying out the board, the footprint for the break-away header is used. It’s small and easy to use. The headers are cheap and easy and you don’t need to stock a bunch of different pin-counts.

That’s all fine and dandy until the next rev of the prototype when you decide to change to a shrouded header for the additional reliability and pin protection afforded by it. When making that change, don’t forget that the footprint with the shroud may very well be bigger than the break-away footprint.

Shrowded header In this particular case, it wouldn’t have mattered except for the capacitor that ended up under the shrouded header.

Duane Benson
Get out of my cap’s space, man

http://blog.screamingcircuits.com/