A600 recapping and solder balls

[ppsh41]

Hi all,
I'm trying to recap an A600 and I need some help.
No problems at all in removing capacitors, all pads are intact and cleaned with desolder braid and then with isopropyl-alchool.

When I try to solder new SMT caps, sometimes I have solder balls. I don't think is a good result.



Temp of the iron is around 350 C and the solder is 60/40 old-school.

Questions:
- Why I create these solder balls?
- How to avoid them?
- Can I leave them there, or are dangerous?

Thanks in advance

[Stratosplat]

Way too much solder. They're probably fine, but it's far easier to tell a bad joint from a good one if you can still see the component leg shape through the solder.

[pandy71]

Avoid them by using good flux and not to much solder.
Remove is quite simple - use on of WICK's braid made for absorbing solder.
https://en.wikipedia.org/wiki/Desold...oldering_braid

Good Luck.

[jarp]

Use more flux. Either your solder did not get properly everywhere hence the blob or you used way too much solder but for both cases flux will help. There is no need to use too little flux, just use a lot.

Of course you need to wash flux off afterwards. I like to submerge whole mobo to IPA and carefully brush everything off.

Ps. While blobs won't harm anything per se you still should fix them. Now you do not see if you have cold joints...

[bebek]

Most likely it means that solder did not flow under the cap to cover the pad. Flux should help but next time try to heat it a bit longer adding solder so it will have a chance to flow. Need practise.

[jarp]

Oh and sometimes even when you use enough flux and proper amount of solder you still get blobs like that (too little heat or too short heating time). I've found out that applying some more flux and then re-heating the solder while extremely gently pushing the cap so that the problematic leg rises from the pad for 0.1mm or so helps. Blob will be literally sucked to the pad and leg properly. Then let cap go and re-heat solder one more time to remove possible tensions and you should have a good joint.

So you may be able to fix those blobs without actually removing the solder if the problem is not excessive solder.

[supaduper]

Also use a thin wire solder like .7mm so you can control the flow better

[ppsh41]

Thank you all for your advices, I'll try to reduce the quantity of tin and to heat up a bit more the pad.

What type/brand of flux you can suggest? I use the (probably fake) Amtech RMA-223.

[Kin Hell]

Flux Paste in a Tin (usually dark brown) is messy but gets good flow results. It has high levels of Rosin which ensures good flow.

Some of the more modern Flux Liquids are clear & leave little residue but are harder to get the solder flowing with it.

Important thing to remember:

Ensure both surfaces to be joined are cleaned with flux & tinned with Solder from a tinned Iron. Flux burns off the oxidisation & allows the solder to flow.
Then sweat the two the parts together by applying a tinned Iron again. Feed more solder into the join of required, but go careful.

The blobs you have are indicative of lack of Flux paste. You could dab some flux Paste on them & re-flow with a hot tinned iron.

Search Google so you know what you're looking for.

[pandy71]

Originally Posted by ppsh41

What type/brand of flux you can suggest? I use the (probably fake) Amtech RMA-223.

Use "no clean" flux for SMD devices - rosin based flux may give suboptimal results especially on partially corroded pads/tracks (Amiga is over 20 years old vintage and some chemo physical processes are unavoidable).

[Shadowfire]

Hate to break this to you, but rosin-based flux IS a "no clean" flux.
The low solids no-clean fluxes don't leave a residue like rosin, but they evaporate very quickly when heat is applies, and I wouldn't recommend using them unless you are soldering using solder paste / balls.
And, of course, I highly recommend AGAINST using fluxes that aren't of the "no clean" variety, since then you need to wash the board properly to avoid corrosion.
Finally, remember that even "no-clean" fluxes need to be brought up to soldering temperatures to activate and avoid corrosion. Just slathering the flux on won't prevent corrosion - you need to make sure it all gets heat up, and the best way to do this is with a heat gun.

[pandy71]

Originally Posted by Shadowfire

Hate to break this to you, but rosin-based flux IS a "no clean" flux.
The low solids no-clean fluxes don't leave a residue like rosin, but they evaporate very quickly when heat is applies, and I wouldn't recommend using them unless you are soldering using solder paste / balls.
And, of course, I highly recommend AGAINST using fluxes that aren't of the "no clean" variety, since then you need to wash the board properly to avoid corrosion.
Finally, remember that even "no-clean" fluxes need to be brought up to soldering temperatures to activate and avoid corrosion. Just slathering the flux on won't prevent corrosion - you need to make sure it all gets heat up, and the best way to do this is with a heat gun.

Yes most of this is true with few extensions from me - there are non rosin based no clean flux's on market, sometimes rosin is ultra clean with special activator to improve joint, i always recommend to clean every solder even one with no clean flux - also visual inspection is easier (important to judge quality of joint).
And i use always activated flux (they are mild not aggressive active but way better than rosin itself - i use also rosin in form of liquid (rosin dissolved in mixture of IPA and a bit of acetone) or solid for less demanding joint usually larger THT components like transformers, large semiconductor etc).
There is group of circuits where no flux remains are allowed (medium/high voltage circuits, circuits with impedance etc).
Personally i always unsolder competent, cleaning pads with wick's, sometimes pad and area is corroded and need to be clean separately - i use for this just good quality rubber pencil eraser (those not smelling nicely - they are usually gray or some not very nice clean color but they have small amount of glass powder that improve efficiency and is relatively safe even for thin layer of gold/silver platting).
After cleaning pads with IPA applying a bit of flux then soldering part - after all area is always cleaned with IPA and visually inspected - never hear any complaints and always people are impressed than place of repair can't be distinguish from industry quality joints.
Works for me and i hope it will work for anyone else too.

[Hewitson]

Just to reinforce what others have said... NEVER do SMD soldering without a good quality flux. I prefer the liquid type which comes in a bottle with a brush attached to the lid. That is the most convenient way to use it in my opinion.