EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: medical-nerd on March 14, 2018, 10:51:34 pm
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Hiya
Regarding solder paste - Sn62/Pb36/Ag2 - what gauge needles do you use to apply this to pads - I'm looking at buying a pack of 25G stainless steel dispensing needles.
These are described as suitable for medium viscosity fluids. Or do I need a wider needle? Can I reuse needles or will the paste set inside?
The paste is supposed to be stored in a fridge - what is the shelf life out of a fridge?
Cheers
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I am using this: https://www.ebay.com/itm/100pcs-22Gauge-TT-Blunt-Dispensing-Syringe-Needle-Plastic-Tapered-Tips/172143718510?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649 (https://www.ebay.com/itm/100pcs-22Gauge-TT-Blunt-Dispensing-Syringe-Needle-Plastic-Tapered-Tips/172143718510?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649)
Cheaper and easier to clean than stainless steel needles.
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Hiya
Thanks - I had not considered those as a possibility, I'll try them. :)
Cheers
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Depends on what type your paste is. Type 3 and 4 are pretty common but may be hard to push through a 24 ga needle. I started with T3 and found it to be difficult to use with smaller gauge needles, even with teflon coated needles. Of course, those are needed for LGA and QFN parts because you want fairly small solder paste dots. I tend to use stencils now so T3 is ok. Next order, I'll get something smaller even though T5 is about double the cost.
To clean, I use IPA (not india pale ale) to clean them with a spare syringe.
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+1 plastic needles. The taper means you can get the paste out with lower pressure for a given gauge. Buy a 50 or 100 pack. They are also cheaper, which is important because you will probably want to just toss them after each use.
I also suggest you buy the black twist on caps for storage. Technically, you could get by with just one per syringe, but it's nice to have an unlimited supply. These are also cheap as dirt when bought by the 100.
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Indeed there are different kinds of paste with different size "balls".
The cheaper is for stencils they have bigger size and they will not easily go through small needles.
What you could to test is buy an assortment metal needles on ebay and test or other option buy plastick needles and use a sharp blade to cut it off so the opening widens.
Also let the paste first get to room temperature it will be much more fluid then when it gets out of the fridge.
Are you going to use a pneumatic timed device or manual?
For the first I bought from Farnell 3cc syringes with luerlock and the insert and end aps (luerlock and endstop) then you can fill it with some paste while the rest remains cooled.
I must say that I have cleaner/better results with metal syringes esp. on extremely small pads
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I struggled with 25G needles - especially with common T3 solder Teflon needles are my go-to for T5 solder used for small features.
From memory - I think I am using 22G for T3 but I have a pneumatic dispenser. Rather difficult to use a manual plunger and maintain accuracy.
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I'm using B.Braun Sterican blunt 21G (the green ones) (Ident 9180109) for solder paste. Problem is getting good solder paste in usable syringes but I do have a supplier of good paste now in Germany.
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I am also curious about how long a sealed can of paste can be left at room temperature before its useless for "hobby" use?
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I am also curious about how long a sealed can of paste can be left at room temperature before its useless for "hobby" use?
I have left paste out for quite a while before it gets dry and difficult to deal with. In general - I try to keep it in the refrigerator as much as possible since I rarely consume it all before it goes bad.
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I am also curious about how long a sealed can of paste can be left at room temperature before its useless for "hobby" use?
When it becomes dry/brittle it is useless.
It is good to cover the stuff inside the can, usually there is an extra plastick lid.
But why go against the manufacturers recommendations?
If you are going to need paste for a few days take some out of the large jar and put it in a syringe, that way you only loose the syringe contents.
I keep my 500g cans in the fridge and that can keep ok for two years, but smaller containers could go wrong earlier.
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I am also curious about how long a sealed can of paste can be left at room temperature before its useless for "hobby" use?
I have syringes with a useable shelf rating of around 6 months at room temperature.
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Btw don't use medical needles, they have an builtin filter making them only pass liquid rendering them completely useless for paste application. Been there, done that, failed.
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Hiya
Btw don't use medical needles, they have an builtin filter making them only pass liquid rendering them completely useless for paste application. Been there, done that, failed.
That is certainly true of filter needles used to draw up drugs. However normal needles do not have inbuilt filters. I have now tried 21g normal needles and it is possible to apply paste, however I have found the resistance to injection because of their 1.5 inch length is just too high for hand injection and I have no control over the amount delivered once I have applied such a high pressure. I am waiting for some short needles and some plastic needles to arrive and will then practice more. Many thanks to everyone for the advice.
Cheers