Holding components without bending leads when soldering upside down?

Question

I am gaining experience in soldering components onto PCBs. I'm working through some one sided through hole PCBs and one thing that I'm having trouble with is holding components once I flip the board. I generally tend to not like bending the leads when I flip the board. There are two reasons -- one being that they still don't seem to fit tightly, not to mention you can't bend the leads of some components (e.g. short lead capacitors) and the second being that they don't solder on nicely. With bent leads, they can even sometimes be touching other soldering points in some cases (after cutting excess off).

The only thing stopping me from attaching all the components and then flipping it and soldering all the leads is that

1. as soon as I flip it components fall out
2. the components which are taller than others (e.g. electrolytics) dictate the other components to fall to that height.

The components falling out when I flip the board I can overcome by using a bit of card to hold them while I flip it. I experimented with some sponge to hold the components in their respective heights when I solder but not much success.

The best I can come up with is soldering in 'layers' with the shortest components first (resistors etc) and slowly building up until reaching the layer of electrolytic capacitors.But again, ideally I would like all the components on the board together and then just solder them all in one swipe.

Any better ways of doing this? Any pointers?

Answer 1

It isn't a solution to all through hole components, but for devices with more than two pins I've taken to designing my landing pads with hand assembly in mind. For instance, with header, the pins can be slightly offset so the pins fit snuggly in the PCB, like this:

Each through hole has an alternating plus or minus 0.05 mm offset from the center (it's a 1.27 mm pitch header, or 0.05", half the normal 0.1" pitch that's so common). I've produced at least four boards with this augmentation and it works well for holding the header flush while I get it soldered. It even makes routing easier in some cases, like a 45° route from a pad where the adjacent pad is recessed will more easily meet clearance rules.

I haven't used any DIP parts recently, but if I did I would likely use a similar method to make hand assembly less of a chore.

For components with only two leads it's easy enough to tin the corner of one of the through hole pads and hold the component in place with one hand while the other wicks that bit of solder to lightly hold a lead of the component in place. Solder the other lead and then finish up the lightly soldered one.

Answer 2

Blu-Tack/Fun-Tak works. It's a removable adhesive putty. Think post-it note glue. Sticks well but easily removed. Can easily hold things in place upside down.

Answer 3

I use a piece of soft foam, possibly with another board to hold the foam flat against the board as I flip the whole assembly so the parts don't fall out, and do the parts in "layers" as you suggest - most parts are no taller than DIP ICs, so this usually just leaves a few large parts to install individually at the end.

On a board of any size, I don't try to install all parts at once - I might stuff and solder all the diodes, then the resistors, then bypass capacitors... etc.

Answer 4

The way you're doing it is fine and will ensure that the low height parts are properly seated. That's particularly important on single-sided boards because pressing down (towards the board) on a part that is not properly seated will directly put the adhesive holding the copper to the board in tension (its weakest direction). If it's properly seated, the force you can exert accidentally is relatively limited for most parts.

Some people use fixtures with foam to push the parts into place. See this answer here for a photo. I can't vouch for the efficacy of this approach.

On certain parts where location and proper seating is vital, you may even wish to solder a single pin or two pins and inspect and adjust the part until it is perfect before soldering all the rest of the pins.

For more of a small-scale production situation, if you have access to the appropriate tools you can make jigs to hold things like displays and LEDs in position while they are soldered.. it's way better than spacers to have a machined aluminum pocket holding the bit while it is soldered exactly in position.