I’ve been trying to get tooled up for doing some reflow solder work on my boards. So far I have found suppliers for almost everything I need, but I’m missing one very important piece . . . . . . a plunger for solder paste syringes.
This may sound stupid, but I have found about a dozen places online where I can purchase Kester solder paste syringes, as well as the needles. But for some reason, I cannot find anywhere that is selling the plungers for the syringes. It’s silly. What I need is about a $1.50 part, but nobody seems to sell them.
I need to do some work on a board for which I don’t have (nor do I want to get) a stencil. I just want to squeeze the solder paste onto the pads myself.
Has anyone found a supplier for those? Or has anyone found a workaround option?
If you’re placing the paste by hand, you’re likely not going to find using the actual tube of paste to squirt out tiny amounts onto each pad very useful – if you’ve never used paste before, you’ll be very surprised at how little you need.
What I tend to do is just squirt a little (and I mean very little) out of the tube onto a piece of paper or something, using the handle of a small screwdriver as the ‘plunger’. The amount you tend to need is remarkably low! I then get a tool that’s essentially a very long pin with a handle, dip it into the paste, and touch it to each of the pads on the PCB so that there’s a little dab of paste on each pad to be soldered. Then squish your parts on, and reflow!
I know others have different methods – some folks squirt immense amounts from the tube onto the pads of QFP’s, for instance, then get out the solder qick – but the amount they use for one side of a QFP is about the amount I’d likely use for several entire boards. You really need very, very little.
I’ve been using Edsyn CR44 solder paste in a syringe, it comes with everything you need. It also has a very long shelf life - I left a blob of it on the bench at room temperature for 2 or 3 weeks, and it was still pliable enough to use for an SMD voltage regulator. The stuff in the syringe is still good for doing fine pitch months later (which is a good job, because I don’t use very much of it, as others have already said you’ll be surprised at how little you need to use)
I’ve found that even using the supplied syringes usually applies too much paste. The best ‘workaround’ method I’ve found to apply paste is with a sewing needle or similar (I used a through-hole resistor lead once). Use it to dab small (tiny) amounts of paste on the pads, then hit them with a fine-tip soldering iron (or reflow it). You may or may not want to use liquid flux if you’re soldering by hand. It makes your joints flow better, but it spits when it boils and can cause the solder balls in the paste to jump away from the joints, leading to possible shorts.
Once you get the hang of it, though, you can even solder leadless QFN parts with ease.
I just got back from Maker Faire Austin and we demonstrated a number of techniques on using SMT parts. I personally recommend the syringe and small needle for fine pitch parts. I can’t imagine putting paste down with a toothpick or small needle. We also demonstrated applying paste with kapton stencils in a method similar to the SFE tutorials.
www.waasco.com is my favorite supplier of paste (kester).
ohararp:
I just got back from Maker Faire Austin and we demonstrated a number of techniques on using SMT parts. I personally recommend the syringe and small needle for fine pitch parts. I can’t imagine putting paste down with a toothpick or small needle. We also demonstrated applying paste with kapton stencils in a method similar to the SFE tutorials.
www.waasco.com is my favorite supplier of paste (kester).
I buy the jars (or jar really, unless you’re a production house it lasts forever), as not many retailers offer the syringes in lead-free formulations. You could either load up your own syringe with this method, or do dabs. I imagine you can get better control with a syringe, but just dabbing solder paste around works very well, though sometimes ends up with uneven amounts in various places.
I will have to find a syringe and try it out however.
Dealextreme sells solder paste for around $4.00, shipped, for a 50g jar. I have some (Lodestar brand) and it seems to work as well as any other solder pastes I’ve tried. Being sent around the world through the mail didn’t hurt it, I do keep it in the fridge now.
Use a syringe if you have access to one, but the toothpick method is surprisingly effective.
Dealextreme’s website appear to be down right now, which is not a common occurrence so I hope they’re still in business.
macegr:
Dealextreme sells solder paste for around $4.00, shipped, for a 50g jar. I have some (Lodestar brand) and it seems to work as well as any other solder pastes I’ve tried. Being sent around the world through the mail didn’t hurt it, I do keep it in the fridge now.
Use a syringe if you have access to one, but the toothpick method is surprisingly effective.
Dealextreme’s website appear to be down right now, which is not a common occurrence so I hope they’re still in business.
It’s actually kind of common, happens all the time for me.
I always thought the paste on DX would not be real solder paste. From what your saying we can infact use this paste for reflowing? If so that’s great, its so cheap and easily available.
You have to make sure you’re looking at a solder paste listing, and not a listing for paste flux. But yes, the paste I have is very smooth and melts cleanly on the PCB.
I haven’t tried reflow with the Lodestar paste, but it does work just fine for hand soldering. As mentioned it is a smooth paste. The DX website is up now (at least for me), and $3.78/50g is hard to beat.
The hard part for me is shaky hands with little parts…I either need more or less caffeine.
There is about 6 choices… I guess when I get an oven together I will just test all of them. Although I would assume the most expensive is probably the best quality like most things on DX.
The paste was the only part of the “diy reflow oven” equation I was missing, now I know I can get paste cheap and easily I will have to put an oven together for sure.
Edit:
Now I remember why I dismissed all the DX “Soldering Pastes”, 7 of the 8 “Soldering Paste” products are flux, I think this one (http://www.dealextreme.com/details.dx/sku.4711) is actually soldering paste though.
Edit2:
$3.78?? Mine shows as $3.73… maybe I have a better price as I buy lots there… never noticed that before.
I found a workaround to my lack of a plunger for my Kester syringe. Seems kind of stupid now, but a 7/16ths dowel rod cut to about 4 inches long worked like a champ.
I got my Kester solder paste from waasco, along with a small packet of epoxy needles that easily fit on the syringe for dispensing across the board. I opted for the second day delivery method to save some cash, and the paste arrived in perfect shape nestled in its Styrofoam box with a freeze-pack.
I have to admit that I was inspired to finally give this a try after visiting Maker Faire last weekend. While there, I ran across Mr. Ohararp.com doing his demo of the technique. Thanks to the local Goodwill, I acquired my reflow oven (read toaster oven) for $12, and it reflowed my first trial board perfectly. One small solder bridge was easily cleaned up with some solder braid.
My next experiment will be to send in my gerber file to have a stencil cut. Does anybody know if doing so gets a stencil that only includes the SMT pads? or does the stencil also have cutouts for the through-hole components?
Is reflow even possible on through-hole components? I checked datasheets and all but one of my through-hole components states it will withstand reflow temperatures. Any thoughts? Horror stories? Success stories?
spiffy_chimp:
My next experiment will be to send in my gerber file to have a stencil cut. Does anybody know if doing so gets a stencil that only includes the SMT pads? or does the stencil also have cutouts for the through-hole components?
Depends on how you export the stencil layer. You could include the drill holes in it, or attempt to only include the copper relief, but there generally won’t be enough solder paste to nicely fill the plated hole via stenciling application. Manually dispensing would work.
In practice, through hole components are not usually done in reflow. They’re usually wave soldered. Though you can use an intrusive reflow method, usually as a second operation.
