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Old Today, 02:11 AM   #5681
suzyj is offline suzyj  Australia
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Join Date: Jan 2006
Location: Western Australia
There's absolutely zero reason to be frightened of surface mount components. I find the bigger ones (1206) much easier to deal with than through-hole components.

Here's a couple of photos of one of my latest amps part way through loading, to show details of the process. This is built with 0204 MELF resistors (similar dimensions to a 1206, but round), 1206 capacitors, MELF diodes, and SO-8 ICs.

I don't use hot air - I simply use a reasonably fine soldering iron tip (these were done with a Metcal STTC-037 tip, which is a 1.8mm chisel. I use gobs and gobs of RMA flux (in the syringe) to coat every pad, then apply some solder to one pad for each component. You can see this on some of the components - I ran out of 1Ω resistors. Then I hold the component in place with tweezers, reflow the solder, then solder the other end.

The additional flux is really really important to ensure good quality joins. If you don't have ample flux on the work, the reflow for the first pad just doesn't work properly.

RMA flux is the only stuff I use - both personally and in the lab I run for work. The reason for this is that it works well to clean oxides, and - importantly - is really easy to get off the PCB afterwards. Many industrial processes spec no-clean flux, which you can leave on the PCB for consumer junk. No-clean flux doesn't work very well to remove oxides though, so you've then got to be really anal about component manufacturing dates and storage. On top of that, if you do want to clean the flux off, it's all-but impossible to remove.

Same applies to the flux in the solder wire - that's gotta be RMA too, for exactly the same reason. Luckily all the solder manufacturers (Kester, Multicore, etc) cater to PITA old EEs like me, so the stuff is easy to buy.

After I'm finished doing the surface mount parts, the board gets dipped in boiling water from the kettle to heat it up, then I splash a little Safewash (Electrolube Safewash Original 400ml from Electrolube Mektronics Australia) on and scrub it with a toothbrush. Safewash is a water soluble detergent-based flux remover, and works a treat on RMA flux, especially if everything is nice and hot.

Then I add the through-hole components. If everything is nice and new, as it is for this PCB, I generally don't worry about additional flux for the through hole stuff - what's in the solder is plenty. Once that's all done, the PCB gets a second scrub in hot Safewash, followed by a rinse in hot water and a bake in the oven for a couple of hours at 60-80 degrees.

There's just way too many advantages with surface mount parts - components on both sides, higher stuffing density, better quality components, lower parasitics - not to use them.

Edit: And I just spotted a couple of pads (caps - top right of the PCB lower) that I missed.
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File Type: jpg IMG_0419.jpg (701.0 KB, 135 views)

Last edited by suzyj; Today at 02:18 AM.
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Old Today, 06:56 PM   #5682
joztom is offline joztom  Slovenia
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Join Date: Feb 2011
Location: Ljubljana
First version were built in 1988, this last is current feedback +50V/0/-50V or more, double sided with ground planes, non SMD elements, pure discrete construction, and total symmetrical scheme with servo null. Rail to rail voltage on driver, all DC coupled, compound type end stage, 100*84mm with direct mount on heat sink. Exist in SK/SJ, Exicon and IRFP output transistor version.
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