Electronics > Beginners
How can I get Solder Paste from a syringe to stick?
Bud:
I am using a 20 Ga needle for 0805 and 23 or 24 Ga tor anything smaller and 0.5mm pitch ICs (under microscope)With a good paste there is no problem with paste sticking to pads. I am sure your problem is with the paste you are using. Two brands I am using (lead no-clean 63/37) are Kester 256 and MG Chemicals 4860. Done thousands of pads. I would say do not buy on Amazon, you may get repacked expired paste. I used to buy from CML Supplies but the last time i got same problem as yours, the paste did not stick. So i dropped them and buy locally from parts distributors. More expensive but very good paste.
Edit: I use small 3-5ml syringes filled with paste with maybe 1/4 of volume, that makes application easier. I have 2-3 Luer lock syringes on the bench with different diameter needles fitted, all bought at a local medical supplies store. I do not recommend using the stock syringe in which the paste is shipped, that would be very difficult to squeeze.
Psi:
I have come across this exact problem many times when pasting a PCB using a syringe.
I found it very dependent on what brand of paste you get. I had lots of issues with Chipquik paste.
The paste has to be somewhat 'wet' with flux to stick to the PCB from a syringe, so if it's old and some of the flux has dried up this will cause problems.
A paste with a higher flux content will also work better.
Also try a few sizes of dispensing needles. Some sizes work better than others.
A warm PCB will also help the flux to warm-up and 'melt/stick' to the PCB pads when it comes into contact.
But this is not usually needed. Perhaps it might be useful if you live somewhere that's very cold.
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