両面プリント基板の表と裏を繋ぐために要所要所に穴を開けて線を通してハンダ付けするのですが、自分で作ったやつはどこかがうまくつながってなくて正常に動きませんでした。
テスターで確認はしたんですけどねー。
業者に頼むとその穴にメッキ加工をしてくれて、何もしなくても表と裏が繋がるので確実なんですよね。
この加工はさすがに個人じゃ無理です(やってる人がいるのが驚きですが)。

両面基板自作の過程はもし工作編を作ることがあれば描こうかとー。

In order to link the front and back of a double-sided PCB substrate, I drilled holes where needed, passed wire through them and soldered it in, but something wasn't connected right in the ones I made, so they didn't work properly. I did confirmation with a tester, though.

If you ask the supplier, they'll put plating on those holes, so the front and back will be connected without you having to do a thing, which is reliable. Naturally, doing such plating on one's own is infeasible. (Though surprisingly, there are those who do so.)

If I ever make a construction chapter on my process of making a double-sided circuit board myself, I guess I'll draw it.