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Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
does anyone have experience with these ultra low melting point solder?
solder product : similar thread :
281F seems real low, perfect for my soldering of tiny SMT devices without the pins visible or accessible. I plan to etch my own boards, then use a sewing needle to put down solder paste, and then using a normal soldering iron--heat the trace and let the heat conduct under the device and met the solder. One pin and trace at a time.
or possibly just use a toaster oven (not for human food ever again) and do it all in one go.
does any one have any experience with similar circumstances? remember the accels and gyros are leadless so theres no getting then directly hot with the soldering iron.
ive looked here on 4HV and on SparkFuns' website and I think I can pull this off one way or another, given what others show.
Registered Member #3215
Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780
frying pan and thermostatic control... it is uniform and will heat through the PCB evenly, and the heating and cooling curves wont be too harsh on the SMTs
Registered Member #1792
Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527
Patrick wrote ...
281F seems real low, perfect for my soldering of tiny SMT devices without the pins visible or accessible. I plan to etch my own boards, then use a sewing needle to put down solder paste, and then using a normal soldering iron--heat the trace and let the heat conduct under the device and met the solder. One pin and trace at a time.
The usual technique for that type of package would be solder-paste with oven reflow.
I've used a technique like you describe with standard (lead-based) solder. I'd melt a bit of regular solder (not paste) onto the pads, add some paste flux to each pad so the part will stick in place and put the part down. Then I would sometimes preheat the board partially using a hot air gun or a toaster oven (with board wrapped in foil), or with a big soldering iron on the ground plane. Then I'd heat the traces one at a time to reflow the solder onto the part. Could also do the whole thing with hot air gun.
I was usually doing rework, not the whole assembly, so I never tried to reflow an entire board in a toaster oven.
If you're doing DIY boards without soldermask it will be more difficult because the solder will want to run down the trace rather than stick to the pad if the trace heats up to solder melting temperature before the part pad. But there are some DIY soldermask techniques ( which will make hand soldering or oven reflow of these "blind pad" packages easier.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
TY everyone for the responses.
I was thinking of the solder mask, that does worry me.
Mattski there is a CircuitWorks product that's almost as good as solder mask, but its meant as a conformal coating. In any case, its a mag, gyro and Acc, so 9 DOF IMU, with about 30 pins all together, and yes they are totally blind, I just need them to be on a circuit board about 1" sq.
allot of the similarly constructed devcices look like the inside of an ipod nano , tiny ICs and traces all over, with no visible solder pads...
Registered Member #2939
Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615
You would be best to paste and place the whole board then reflow in a toaster oven. Use a thermocouple meter to check the oven temp. In our one we cut the heating power by putting a diode in series with the element - crude but it works. You don't want too high a ramp rate. Also shield the element with some ali mesh, so less IR heating. Process is to start oven from cold with board in place, heat to predetermined temp, we used 210C for lead solder. When solder is molten tap pcb gently - this helps all the parts align to pads (surface tension on solder helps this), then switch off and allow to cool in oven with door open. Solder paste is easiest to apply with a syringe + hollow needle. If you are doing a bunch of the same boards you can make your own paste stencil using 0.005" brass shim stock - etched in FeCl3 as you would a pcb.
We have built pcbs this way with a 32 pin BGA (an accelerometer)
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
2Spoons wrote ...
You would be best to paste and place the whole board then reflow in a toaster oven. Use a thermocouple meter to check the oven temp. In our one we cut the heating power by putting a diode in series with the element - crude but it works. You don't want too high a ramp rate. Also shield the element with some ali mesh, so less IR heating. Process is to start oven from cold with board in place, heat to predetermined temp, we used 210C for lead solder. When solder is molten tap pcb gently - this helps all the parts align to pads (surface tension on solder helps this), then switch off and allow to cool in oven with door open. Solder paste is easiest to apply with a syringe + hollow needle. If you are doing a bunch of the same boards you can make your own paste stencil using 0.005" brass shim stock - etched in FeCl3 as you would a pcb.
We have built pcbs this way with a 32 pin BGA (an accelerometer)
excellent, I will look at the temp profiles on the datasheets, and try to mimic them... as best a toaster oven can. Spoon, did you have traditional solder mask when you made yours?
Registered Member #2939
Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615
No, no mask. our homebrew pcbs never got that sophisticated. I do think it helps a bit to pre tin the board first. To do this I paint the board with flux, then wrap a piece of desoldering braid around a soldering iron. The braid gets loaded with a bit of solder then used like a felt tip pen to wipe solder onto all the copper. You want a very thin layer of solder - no obvious blobs. Looks pretty, and makes soldering easier.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
ok got it.
apparently it needs to be kept cool. It shipped with a reusable cool pack. but both the cool pack and the solder were room temp, despite next day air 61$ shipping, which digi-key recommended.
the problem is I fear there maybe an expiration date, like milk. My silver epoxy has such a date, yet it works and I don't use it often enough to run out. I dont think ill use 15g of this special solder in lets say 2 years.
there is a "filled 4/13 label" present.
pics to follow:
the solder syringe...
I cut some of the label away so I can guage my usage.
the bicopter drone "Taharqa" all of this is meant for...(civilian, academic version seen here)
Registered Member #2939
Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615
Store it in the fridge, but let it warm to room temp for use - it will be too thick otherwise. The only thing that happens to solder paste as it ages is the solvent in the flux slowly evaporates, eventually resulting in paste too thick to apply properly. Keeping it cold slows this process down. I've used paste waaay past its expiration date and it solders just fine.
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Low Melting Point (281F) Sn/Bi Solder for SMT.
