I use metcal.
Last edited by gramo; 22nd April 2007 at 11:36 AM.
I use metcal.
What kind of price range are they? Do you have any links to international sellers?
I have the 850 SMD hot air gun. It works. I only use it for rework, repair and very small jobs. I use one of the smaller tips and heat a small portion of the board at a time.
I use a “toaster oven” to heat the entire board. I heat the entire board with parts at 100C for a couple minutes. Then turn the heat up to max for 8 to 10 minutes. I watch the board very carefully. At temperature the solder turns from gray to silver. When all the solder is flowing I turn off the power and open the door. Wait for the solder to setup (seconds) and done. There is a temperature curve you should follow but I found my process is close to the curve. On recent boards I place a large pad in each corner. These pads get a drop of solder past. It is hard to see under parts but the 4 large pads are easy to see and when all 4 drops of solder is silver colored then the board is at temperature.
So you put down your solder paste, layout every device, and the heat them all up simultaneously, then do any rework with the heat gun?
Enough drilling holes, eh? It seems there are several people on this forum heading towards SMT, self included.
Gramo, do you know about SparkFun?
They have a lot of info on surface mounting, including a design or two for toaster oven controller, and some videos of hand soldering surface mount parts.
They also sell a couple of rework stations, but they are almost double the price of the ebay link you posted. I noticed that the seller on ebay also offers solder paste and dispensers, etc. Thanks for that link!
Get yourself a good pair of tweesers! I got a rather expensive hand vacuum pump, but it doesn't work all that well.
Right! Everything at one time. The solder paste holds the parts down until you are ready. When the parts are hot and the solder is liquid the parts move slightly, they align themselves. I have not done a board with parts on both sides. I know people that do it. I may just put 5 capacitors on the back side and just hand solder them.
My toaster oven came from a used store for $5.
The temperature curve is posted here. I do not follow the curve carefully. At first I measured the temperature carefully but soon learned better. I know what setting produces 100C. I put the board in. Set to 100C. Wait for a while. Then go to full power. Watch all the solder to flow. Maybe wait 30 seconds. Open the door and wait for it to cool.
I have been avoiding going to surface mount but would like to.
How well has surface mount worked out for you.
Does it save much time?
If you make your own boards do you place you via wires using the paste?
How often do you have to fix shorted pins which would be caused by what? too much paste.
Sparkfun's SMD sets are supposed to be good quality for the price. They have a lead-free version too (higher temp).
SMD paste may recommend a lower temp pre-bake that forces the solvent and flux out of the paste before the high temp to melt the solder is applied.
SMD can also be done in a toaster oven, doing the whole board at once. This is faster than mounting each component by hand. These hot air kits are great for rework though. Otherwise, you have to be a real wizard of technique or just use ChipQuick alloy solder to remove them.
Some parts can't be done in an oven or even with hot air. I've seen plastic-cased pressure sensors stated as such in their spec sheets, they won't take the heat. I think the best solution is to leave enough exposed copper pad around it to use a conventional iron to wick solder onto the pads or leads.
I thought what I'd do was I'd pretend I was one of those deaf-mutes.
I have boards made for me so I do not have to run wires through the holes.
I can get very low cost boards by not doing silk screen. OK for through hole but bad for SMT. The silkscreen helps keep solder on one pad from connecting to the next pad.
I found that even with solder paste connecting all the pins together; the molten solder retreats back to only the pads. On a resistor I only put paste on the two pads with a toothpick. On a PLCC IC I put a line of paste connecting all the pads together. With little to no practice I got the right amount of paste. You might try one practice board. Try too much paste on one part and too little on the next and see what happens. The paste reduces to about ½ that much solder.
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