Any tips for hand soldering 0402 components?

how to solder 0402 caps

In the past, I've used alot of 0603-sized components in my PCB design, now I need to go 0402 and that's in my eyes very small. I cannot reflow solder them since my available equipment is limited to a reflow oven and the batch of the 0402-components are decoupling capacitors on the bottom layer under a BGA DSP chip (which I need to reflow solder).

I do have a solder paste dispenser pistol (with flux in the mix), should I just try to apply small solder balls to the pads, placing the component then tapping each side with an iron under a magnifyer, or should I use a flux pen and tin? any tips?

I am especially concerned about flux sticking between the pads under the component where I cannot easily clean it. I've got 20+ decoupling caps on each of two power rails, so if any conductive fluids sticks underneath the capacitors, I'm in trouble..

Also, if anyone have any tips on cleaning flux from these tiny chip-capacitors, I'm all ears.

Generally, for prototype or repair, you should use "no-clean" flux only. I think, most of the fluxes used in SMT don't produce conductive residues, but you should know for your utilized products. From this prerequisite, I don't see a particular difference between 0603 and 0402 parts in reflow soldering, apart from some size difference. I generally use 0402 decoupling capacitors at the bottom of FBGA components, particularly FPGA, cause they exactly fit the pin grid. The assembly companies are not having issues with it, even a small company, that assembled of BGA components for the first time two years ago on my request (with serious doubts in the beginning).

Yeah, use non-cleaning flux or, anyway, you don't have to worry a bit about flux...just clean it with alcohol or paint thinner. bath the board with those chemical and use a soft brush to reach all the corner.

rikie_rizza said:

Yeah, use non-cleaning flux or, anyway, you don't have to worry a bit about flux...just clean it with alcohol or paint thinner. bath the board with those chemical and use a soft brush to reach all the corner.

Click to expand...

You said bath. Do you really mean soaking the entire board with chips and everything after soldering?

Yes I mean that...it okay thou, it will vaporize anyway. After the bath, to make sure it is really2 dry... use a hair drier or other hot air blowing equipment. Or if you dont have it... don't worry, it will dry.

Best choice is alcohol, try above 70%. Paint thinner is abrasive and could damage your solder mask or other optical device on your board (such as clear epoxy led).

I have experience in hand assembling SMT PCBs with very small components and I have found, personally anyway, that it is best to tin one pad of the footprint and then introduce the 0402 with tweezers.

It may take some practice to solder the free end while not reflowing the other end which was soldered first though.

I have tried dispensing solder paste onto pads but found it awkward. One of the other methods I have used which was very successful was to make a solder stencil out of an old stencil.

If you don't have an old solder stencil to cut up you can use metal shim, using a PCB drill bits by hand you can drill holes in the shim. They don't have to be exactly in place as the surface tension of the solder pulls the components onto the pads during reflow (don't use an iron).

Had the same problem a few years back, I now have it with 0201's, but that's another story an the nightmare is not over as I've told we will go into 10005 next year.
We ended up using micro soldering tweezers (basically to mini soldering tips on a tweezer set up) they are made by JBC Tools and while they are expensive, they have been a life saver as the other alternatives were working with hot air which blew all surrounding components away or having to buy very expensive machines which are not justifiable for our low production levels.