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Old 17 January 2019, 18:19   #1
Sim085
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Solder paste

Hello, I am planning to order solder paste to solder one of the smd capacitors back to the motherboard.

I have found the following;

"SOLDER PASTE, SN, BI, AG, 138DEG C, 15G SMDLTLFP By CHIP QUIK"
https://www.amazon.co.uk/gp/product/...SAJREEZF&psc=1

Would this be good for the amiga?
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Old 17 January 2019, 18:21   #2
ajk
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Surely it'd be a lot easier to solder a single resistor with just an iron and solder wire?
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Old 17 January 2019, 18:25   #3
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Well... It's a special low-temperature, lead-free paste, and it's probably a good one at that... But the simplest for the Amiga is old-fashioned leaded paste. Mixing solders isn't ideal, and the solder already on the board will be leaded. I would go for 63/37 paste.

But honestly, for just one capacitor, you could do it with an iron and solder wire instead and save the cost of the paste. It's easy enough with an iron anyway. Even if you want to use hot air to solder it, you can tin the pads with the iron and some solder wire, then put some flux on the capacitor contacts and put it in place, using the hot air to melt the solder again.
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Old 17 January 2019, 18:34   #4
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When I replaced the SMD caps on my A1200 I used regular leaded solder wire.

Clean both pads then tin one of them. Align the cap and hold it against the tinned pad with tweezers then melt the solder. Once it's flush with the board tin the exposed part of the other pad. The solder will flow right under.
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Old 17 January 2019, 19:29   #5
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Get thin (0,5-0,4mm in dia) leaded solder wire instead.
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Old 18 January 2019, 00:50   #6
Sim085
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So I went for normal soldering for the cap, however I think I will also have to replace the LF347...wouldn't solder paste be better for such a job?



Quote:
Originally Posted by Daedalus View Post
But honestly, for just one capacitor, you could do it with an iron and solder wire instead and save the cost of the paste. It's easy enough with an iron anyway. Even if you want to use hot air to solder it, you can tin the pads with the iron and some solder wire, then put some flux on the capacitor contacts and put it in place, using the hot air to melt the solder again.
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Old 18 January 2019, 04:48   #7
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Quote:
Originally Posted by Sim085 View Post
So I went for normal soldering for the cap, however I think I will also have to replace the LF347...wouldn't solder paste be better for such a job?

Solder paste is just generally more expensive and doesn't keep as well as regular solder, so use it sparingly or when you really need it. You wouldn't really need it for the LF347 either as long as you have some flux.



You don't really need hot air for little chips either if you have some copper wire or wick.
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Old 18 January 2019, 05:44   #8
Hewitson
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Quote:
Originally Posted by grelbfarlk View Post
You don't really need hot air for little chips either if you have some copper wire or wick.
Agreed. I wouldn't even dream of using hot air for such a basic repair. And with all due respect hot air can be dangerous for the inexperienced, I think an iron is the safer way to do it.
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Old 18 January 2019, 12:51   #9
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Solder paste is expensive, don't last long, and it must be stored at low temperature (it go into the fridge).
For few repairs is not a good choice.
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Old 18 January 2019, 21:39   #10
lesta_smsc
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Solder wick and flush are your friends. Amazing how much flux helps prevent burning the pads lol
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Old 18 January 2019, 23:17   #11
Krashan
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Quote:
Originally Posted by Sim085 View Post
"SOLDER PASTE, SN, BI, AG, 138DEG C, 15G SMDLTLFP By CHIP QUIK"
If you insist on using solder paste, never use low temperature paste based on bismuth (Bi). Joints made with it degrade in presence of lead (Pb), are also less stable. It will also make further repairs more difficult, as joints made with this paste will melt 50°C "earlier" than the rest (contamination with lead pushes melting temperature even lower).

Just use traditional Sn63Pb37 paste with lead.

I also agree that recapping using iron (or hot tweezers for removing old caps) is more safe, as the heat power of iron (60 to 80 watts) is much less than of hot air (300 to 700 watts) and is applied more precisely.
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Old 18 January 2019, 23:46   #12
nexus
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if you dont have flux at least make sure its rosin core solder
but ideally for such simple type repair you should have "good" solder a iron and even if you use rosin core should always have flux of some kind ready be a flux pen or whatever floats your boat
this guy explains a lot about the types
[ Show youtube player ]
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Old 18 January 2019, 23:56   #13
idrougge
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Quote:
Originally Posted by Sim085 View Post
So I went for normal soldering for the cap, however I think I will also have to replace the LF347...wouldn't solder paste be better for such a job?
No. It's big enough for any sensible soldering iron.
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