There are several effective methods for removing solder from a PCB hole. Excess solder filling a hole happens quite often. Usually, the clog is residual solder that occurs when an existing electronic component is desoldered and removed.
PCB hole accidentally clogged during soldering
My favorite desoldering tool is a desoldering bulb, which is also called a solder sucker.
To remove excess solder from a hole:
Desoldering hole with soldering iron and desoldering bulb
Unfortunately, the vacuum action of the bulb also removes the solder from the tip of the soldering iron. To prevent damage and to allow for maximum transfer of heat to the next clogged hole, regularly reapply a coating of fresh solder to the tip of the soldering iron. (This is called “tinning”.)
Another effective technique is to use a small hand drill or a pin vise (McMaster-Carr #8455A31 or #8455A16) with a miniature drill bit.
Pin vise used as a hand drill
For many PCB layout programs, the default hole size is 0.029 inches, which is a #69 drill (McMaster-Carr #2912A247). Of course, you'll want to purchase a variety of drills depending on the sizes of the holes that you need to unclog.
Be careful. Using an oversize drill will remove the through-hole plating that connects the trace from one layer of the board to another layer. The loss of electrical connectivity may prevent the circuit from working.
Select carbon, cobalt, or high-speed steel drill bits, not carbide. Carbide will stay sharper longer, but is brittle. Therefore, carbide is only appropriate for industrial repeated drilling in a rigid setup, not a hand drill.
Drill removing excess solder from hole
Only the tip of a drill has cutting blades. The sides of a drill are dull channels for the material. So, reinsert the tip multiple times if necessary rather than spinning the sides of the drill in place.
I find that sucking out the solder with a desoldering bulb and then drilling out any remaining solder is great combination.
On the other side of the aisle, there are people that swear by desoldering braid. It consists of tiny woven copper wires that wick up adjacent solder when heated.
The idea is that you place fresh desoldering braid on top of the hole (or anywhere with excess solder), and then apply heat to the braid using the tip of the soldering iron. When the braid is saturated with old solder, you simply snip off the end.
Other people recommend pressing a thin rod into the solder-clogged hole while heating it from the other side with a soldering iron. The rod mechanically pushes out the molten solder.
Tip of mechanical pencil
To prevent the rod from becoming soldered in the hole, people use materials that are difficult or impossible to solder. Examples include: carbon pencil lead, stainless steel, or wood (toothpick).
There is one last approach that is practical if only one hole is clogged per component -- do nothing. Later on, when you want to solder a wire or component in the hole, simply heat the wire or component lead while pressing it into the hole. The solder will melt.
If you have a better approach than those mentioned above, please let me know.
On the next page, I show how to make your own desoldering tips out of Teflon. Specifically, I made a narrower tip for my desoldering bulb.