Dwayne,
I too have worked on a lot of raw uncoated copper boards. One of my customers had a board with tons of surface mount parts on it that we went through 30-40 iterations of until he got his design nailed down. Once we got solder masked boards and were able to run them on the pick and place it was a breeze except for the few 0201 and 0402 parts I still had to hand solder.
I agree that tinning them would be a good idea but I've always soldered my prototype boards without tinning. I found that for larger parts with lots of leads that it was almost impossible to get the tinning consistent enough to have the part lay flat on the board. It's hard enough with an unmasked raw board getting the parts position correctly, but red neck tinning doesn't seem to work well. Sometimes when tinning those boards you can put too much solder on the traces under the part and it won't sit flat. The few times I had to tin, I tinned lightly with a soldering iron and then reflowed with more flux and a hot air re-work tool to get it to smooth out.
I honestly haven't had that many issues with it. I fluxed the leads of the part and the pads on the board. Put a blob of solder on my soldering iron and after positioning the part I tap two opposing corners to tack it down. Works 99% of the time. Then I drag solder everything else and clean up the tacks last. We were using water soluble solder and liquid flux. Haven't had as good of results with rosin core or no-clean.
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Erik L. Knise
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Erik L. Knise
Seattle, WA
On Fri, Nov 7, 2014 at 8:37 AM, Dwayne Reid dwayner@... [Homebrew_PCBs] <Homebrew_PCBs@yahoogroups.com> wrote:
The problem with all of the suggestions made so far is that everyone is assuming that the pads already have solder on them.
But this is a brand-new home-made board with bare copper pads.
The first step is to tin all of the pads. Use lots of flux - gel or paste flux works best but standard liquid flux will also work. Flood all of the pads with solder, then apply more liquid flux on top of the solder blobs. Hold the board vertically with the pads vertical, then use a soldering iron to draw the solder down to the ends of the pads and on to the tip. Rotate the board 90 degrees and repeat until all of the pads are tinned and cleaned. The pads should now have a thin, smooth layer of solder on top of the copper.
Do a very good inspection with magnification to ensure that you don't have any solder bridges. Then follow the (excellent) advice already given.
Hope this helps!
dwayne
PS - we used to make hundreds and hundreds of our own PCB's in the early days of our business. We would clean the boards mechanically with a fine-grit sander followed by a 3-step chemical cleaning process. Blow the boards dry with warm air from a vacuum-cleaner motor, then feed the boards through a GBC laminater (modified for lower temperature and higher speed) loaded up with Dupont Riston dry-laminate film. Exposed the boards with a modified mercury-vapor expose lamp and vacuum frame, then developed the exposed boards with a soda-ash (potassium carbonate?) solution. Stripped the remaining laminate in a caustic-soda (sodium hydroxide) bath, rinsed, then etched in an Ammonium Persulphate bubble etch tank.
The whole process worked very well but it just took too much time. We eventually went to CNC milling for PCB prototypes (several years), then quit that and just started using APC for prototype boards. All of our production boards are now made in China - the quality is extremely high and the cost is astonishingly low. APC still does our prototype boards.
dwayne
--Dwayne Reid <dwayner@...>Trinity Electronics Systems Ltd Edmonton, AB, CANADA(780) 489-3199 voice (780) 487-6397 faxCustom Electronics Design and Manufacturing