Solder paste.. why is it so hard to work with?

Hello Mario,

I'm using a solder paste from Farnell (Multicore SN62RA10BAS86) which is leaded and rather old. I bought some needles (I think from an EFD dispenser) and fitted a green one (colour denotes needle bore but I don't know the code). You do need to push hard (and then pull back once the stuff starts to flow) but I have no problem putting down solder for 0603 pads. I don't use a reflow oven just a very fine tipped iron and one of those hollow tipped ERSA things for fine pitch ICSs. My solder is gray and opaque so you are either using too fine a needle or you need to eat more spinach.

The more boards I do the less I use solder paste for resistors. The fastest way to do them (by hand) is to use fine solder wire with a flux core. Put alittle blob on one pad with your iron. Hold the part in tweezers and reflow the solder blob while you fit the part. Then solder the other end. It's rough but quick. 0603 are easy, 0402 are possible (with microscope or good eyes and headband type magnifier).

I don't think you will make a living making boards like this. I make prototypes because I need to test partially assembled boards and I like the control of timing I get if I do it myself.

Email me if you want some more info.

Michael Kellett

I'm using Kester R276 (lead free no clean) through a 1.4mmOD needle that expired in 2003. It's grey. It does take an annoying thumb force on the needle plunger to get the solder out. (The paste is completely at room temp.) The solder paste does dispense like mashed potatoes and I haven't come up with a solution yet to get controllable "shots" of solder paste through a needle. Aside from that, my smd pcbs turn out good.

By the way, I'm currently working on a hot plate technique to dodge buying a toaster oven. My kitchen stove top is electric. I going to try using a metal plate on 2 elements. One plate is preheat, the other is solder temp. I just have to figure out how to shuffle the pcb from plate to plate. Temp sensors are used to calibrate. There's a 3rd plate for cool down.. D from BC

Try this:

It's not true, it's a sign that the people saying that can't read the data about the product. Water soluble fluxes leave corrosive residue that must be cleaned immediately. If that's done, it's fine.

The SIPAD system has a long shelf life and has no particular storage requirements.

Good luck.

try cleaning the board well with alcohol, then you can minimize the amount of flux you need. Brad

On Thu, 22 Feb 2007 17:59:55 -0000, "MK" Gave us:

Bad practice. A good way to detach a termination.

Best to keep BOTH pads free of solder (FLAT IOW), place the part, and place the tip on one termination to reflow it, and then the other, while tweezing it in place, of course. Minimal movement results.

Your English is excellent.

Many of us should say: "Sorry if my English is far from perfect: it *is* my native tongue."

Ed

Just wondering - what would happen if you took the bare board, cleaned it up with some fine steel wool, preheated it to, say, 250F, and plopped it on top of a puddle of molten solder? Would it tin the whole thing?

Then you might not even need the paste. :-)

Thanks, Rich

not without flux.

Bye. Jasen

We use an EFD model 1500XL air-powered fluid dispenser, with a small nozzle and between 50 and 80PSI of air pressure. This works well.

The 1500XL has a foot switch which can be used to make a small continuous bead for each row of IC pins, or in a digital timer mode to place a controlled amount of solder paste on a pad each time you press the footswitch. In practice you can apply paste to all the pads on all your boards for a particular component type, then populate all the locations one after the other. We find it takes more time to locate the parts than anything else.

The 1500XL is available at low prices on eBay, e.g.,

We don't use a reflow oven, but do our soldering with a Zephyrtronics hot-air pencil system.

Yeah, sorry I neglected to mention that. When I was working for that battery charger guy, they'd crimp lugs onto the wires (up to like AWG 2 and such), verify a good crimp, and dip them in a solder pot. But before we dipped them in the solder, we'd dip them in a little jug of liquid flux.

I had heard that crimps shouldn't be soldered, but they never seemed to have any problems. Probably because of the crimp - all the solder would do is exclude air; it wouldn't actually be part of the circuit. (If we just soldered the big fat wires into the lugs we wouldn't need fusible links. ;-) )

Cheers! Rich

That's how we used to do it. We had a cast iron bath made up which we filled with solder. We sprayed the cleaned boards with a liquid flux, loaded all the components and then rocked them through the bath (one edge then rotate to the other edge) to solder them.

Actually the solder was an anti-corrosion coating. Other than that, crimp connections do not benefit from soldering.

Except the ones I find all the time in consumer equipment.

greg

Well yes, crimping does benefit from properly trained assemblers with properly operating tools. Of course this is easily detectable as being more expensive ("What you mean 'crimp tool has limited life', just squeeze harder." "But it is an air operated tool, squeezing harder does not apply. The jaws have a lifetime of about 10,000 crimps, ane then should be replaced." "You crazy, i can't afford down time 6 times a day. We replace once a month, like always.")

Consider:

-or-