Author Topic: How can I get Solder Paste from a syringe to stick?  (Read 786 times)

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Offline TimCambridge

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How can I get Solder Paste from a syringe to stick?
« on: March 28, 2019, 07:38:43 pm »
I can apply solder paste to a blank board with a stencil and it sticks just fine.

Working with a syringe is the problem. Videos on YouTube show paste being applied and every blob sticks just fine - that doesn't work for me. I have tried all manner of cleaning the board, and I have tried HASL and ENIG pads.

Maybe there's no solution - my interim fix is to effectively tin the pads but it would be easier to apply a few blobs of paste, drop the component onto the blobs, and get out the hot air gun.
 

Offline AlanS

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Re: How can I get Solder Paste from a syringe to stick?
« Reply #1 on: March 28, 2019, 07:45:30 pm »
These are the questions I would try to answer re you problem:
   Have you tried other brands of solder paste or just the one?
   Has the solder paste aged paste what the manufacturer recommended?
   What temperature has it been stored at since you bought it?
   What temperature are you using it at?

Regards.
 

Offline KL27x

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Re: How can I get Solder Paste from a syringe to stick?
« Reply #2 on: March 28, 2019, 09:55:08 pm »
Paste comes in chunky and creamy, like peanut butter.

Stencil can come out good using larger, coarser solder balls, than syringe.

If the stuff comes out of a little jar, it might be too coarse for a syringe. Then when you push on the syringe, the emulsion can separate, some excess liquid getting squeezed out, initially. And then blobs of solder without enough flux, intermittently fall out.

Temperature is critical, too.

The guys who do it like this this swear by specific brands. Blueskull and some others have mentioned GC10. So, basically, you can't try one solder paste and expect it to work worth a darn.

 
« Last Edit: March 28, 2019, 09:58:18 pm by KL27x »
 

Offline TimCambridge

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Re: How can I get Solder Paste from a syringe to stick?
« Reply #3 on: March 28, 2019, 10:27:24 pm »
These are the questions I would try to answer re you problem:
   Have you tried other brands of solder paste or just the one?
   Has the solder paste aged paste what the manufacturer recommended?
   What temperature has it been stored at since you bought it?
   What temperature are you using it at?

Regards.

The guys who do it like this this swear by specific brands. Blueskull and some others have mentioned GC10. So, basically, you can't try one solder paste and expect it to work worth a darn.

Thanks for the comments.

Currently Warton Microprint SAC305. The previous syringe was different, but these things are darned expensive so I can't really try more than a few. GC10 has its fans but it doesn't seem to be available in syringe form. I'll take the advice and try a different brand when this syringe runs out.

It's new paste (manufactured 02/19, use by 02/20), stored at a cool room temperature, the manufacturer recommends room temperature storage. And I use it at room temperature.
 

Online TK

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Re: How can I get Solder Paste from a syringe to stick?
« Reply #4 on: March 28, 2019, 10:31:24 pm »
In the past I had to deal with dry solder paste and I mixed with alcohol, I don't know if it is the right method (of safe) but it worked help me applying small amounts to the PCB

I don't recommend it for volume production runs...
 

Offline Hemi345

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Re: How can I get Solder Paste from a syringe to stick?
« Reply #5 on: March 29, 2019, 04:12:56 pm »
I tried a syringe and had the same experience.  Now, I just put a little dab of paste on something smooth, like an old anti-static bag, and use a toothpick.  Using a round toothpick I can scoop up a little, roll it against the static bag to make a "worm" of paste on the end of the toothpick, then apply it to the pads.  SOT23-3, 0805, etc pads go pretty quickly using this method but it does take some dexterity. Working the paste like this warms it slightly and seems to go on easy.  Maybe try warming the syringe and the PCB up a little warmer than ambient to see if that helps.
 
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Offline AlanS

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Re: How can I get Solder Paste from a syringe to stick?
« Reply #6 on: March 31, 2019, 08:42:19 am »
I tried a syringe and had the same experience.  Now, I just put a little dab of paste on something smooth, like an old anti-static bag, and use a toothpick.  Using a round toothpick I can scoop up a little, roll it against the static bag to make a "worm" of paste on the end of the toothpick, then apply it to the pads.  SOT23-3, 0805, etc pads go pretty quickly using this method but it does take some dexterity. Working the paste like this warms it slightly and seems to go on easy.  Maybe try warming the syringe and the PCB up a little warmer than ambient to see if that helps.

I think I'll give this a try too. What do you use to do the actual reflow/soldering?
 

Online thinkfat

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Re: How can I get Solder Paste from a syringe to stick?
« Reply #7 on: April 01, 2019, 07:49:03 pm »
It works quite well if you slightly warm up the pcb. It helps the paste spread over the pads and makes it easier to apply as little paste as possible.

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Offline rectumfried

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Re: How can I get Solder Paste from a syringe to stick?
« Reply #8 on: April 02, 2019, 01:47:45 am »
I am about as far away as one could be from "qualified" to comment but what the hell.

Is the problem that it's too viscous or not viscous enough? As others have mentioned, they sell a wide variety of different flii (made up plural form of flux) of different qualities, but more importantly consistency. I bought some flux paste because i was tired of the absolute garbage stuff you get at home depot...Although the flux works better (less crap/carbonized leftovers, better solder flow etc), I can't stand this stuff either. It is so thick it is almost impossible to squirt out. In fact, using the 18 gauge or w.e needle that came with it, I broke the plunger very early on because I had to use two hands with all my strength to get any to come out. For a decent percentage of the remainder of that syringe, every time I needed flux, I had to get pliers out to grab the little that was left of the plunger and push it. I finally had a stroke of genius (and rage) and just smashed the thing open and put it in a different vessel (read: piece of paper....) I do what hemi345 does basically. Have a little bit of 20 gauge wire or just the .8mm solder that I use as an applicator
 

Offline TimCambridge

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Re: How can I get Solder Paste from a syringe to stick?
« Reply #9 on: April 02, 2019, 02:37:03 am »
Thanks for the advice.

The exact symptoms are that I can squeeze a drop of paste onto a pad and it looks just right, but when I move the syringe to the next pad the strength of the paste drags the solder with the syringe.

Of course I could be doing it all wrong :) But my image is that the blob on a pad adheres to the pad well enough to shear off from the needle.

I'll experiment with warming the board and/or the solder by a degree or two.
 

Offline Bud

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Re: How can I get Solder Paste from a syringe to stick?
« Reply #10 on: April 02, 2019, 03:22:55 am »
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.
« Last Edit: April 02, 2019, 03:31:42 am by Bud »
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Offline Psi

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Re: How can I get Solder Paste from a syringe to stick?
« Reply #11 on: April 02, 2019, 03:36:37 am »
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.
« Last Edit: April 02, 2019, 03:38:44 am by Psi »
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