Circuit Building 101

Step 5 Make sure LEDs and Some Capacitors are Inserted in the Right Direction

The longer lead on electrolytic capacitors (the cylinder ones) and LEDs is positive. Insert most components until they lie flat on the board for extra stability unless they have a metal casing that could cause a short circuit.

it's OK if the yellow plastic on ceramic capacitors (disc shaped) goes beneath the top level of the board and touches the solder, it just can't show through to the other side (according to IPC, the industry's soldering standards organization).

Comments

[ac-dc]

Something I seldom see mentioned is that with jacks, plugs, switches that are subject to stress from external user, use, it can be helpful not only to cinch the leads but also manually hold the part against the board tightly while soldering. Eliminating even the very last little bit of play can make the part much more resistant to twisting back and forth later in use. In extreme cases I've even put down a bead of epoxy around jacks and/or during repair work where the aforementioned stress had pulled up a jack or damaged the traces. It is uglier looking to put down the epoxy but which is worse, ugly or broken? For really high stress uses a panel mount jack, switch or plug is really the only way to go without switching to special expensive parts.

[CuriousInventor.com]

Parts are routinely held down with epoxy in automated manufacturing (for instance, to keep SMDs in place for wave soldering), I don't think you lose any points for adding extra.

[ac-dc]

That's hidden under the part. I do a lot of audiophile projects, you might be surprised just how many pains some will go to in order to make a project look nice regardless of whether it's functionally any better or not.