This is not a CAD question, my apologies to those with limited bandwidth.
On occasion, we need to produce small runs of boards with surface-mount parts. We do through-hole boards by hand day in and day out, but surface-mount tech is a mystery to me, so we offload them to a local assembly house. I don't mind paying other folks to do stuff that we don't want to get into, like powder-coating, painting, fabbing pcbs, etc., but it kinda rankles me to pay to have someone build up boards just because I don't know how to do them myself.
Are there turnkey SMD assembly systems for small-volume work? I assume we'd need a way to screen paste onto the boards, smoosh the parts on, then flow the solder. There -- I've shown how little I understand.
There have been several discussions of this on sci.electronics.design. It's actually quite easy for everything down to 0603s (0402s are possible but a bit finicky) except BGA, though for FN packages you need to modify the footprint.
You just need a fine tipped soldering iron, an ordinary one say 2mm chisel tip, fine tweezers, desoldering braid and a flux pen. Oh, and a little tray to put the components in. It's really as easy as through hole when you get used to it.
Flux all the pads before soldering- best proceed one type at a time.
(1) Discretes
Put a blob of solder on one pad (best orient the board so it's the right pad if you're rigfht- handed). Pick the component up with the tweezers, melt the solder blob and position the component. I find it useful to try to pick the board up with the tweezers at this point- it checks the joint is right. When you've positioned all the components, turn the board round and solder the other end.
(2) SOIC
Put a blob on one corner pad - I use top right. Pick up the component with the tweezers, melt the blob and position the component. Solder the opposite corner, then do all the other pins.
(3) Fine pitch packages including quads.
Put a blob on one corner pad. Position the component and solder that pin down- this can take a couple of goes until you get used to it. Then solder down all the corners. Don't worry if pads get bridged a little. Then using the ordinary iron, clean the tip and put a little solder on it. Draw the tip gently across the pins with a smooth action. Finally clean up with desoldering braid- don't be too heavy or you'll lift the pads.
(4) FN packages.
Make a hole in the underside pad big enough to insert a fine soldering iron tip. Solder the component down as for SOIC or fine pitch (finicky as the pins don't rprotrude much) then solder the bottom down via the hole in the underside pad.
Nearly everything I design these days uses fine- pitch SM, and the guys who build it for me hand- assembl;e using these techniques, with success rate approaching 100%.
Yes, and no. The fully automated SMD assembly systems are too expensive to ever amortize with small runs. But for runs of 100, or so boards, you can achieve better efficiencies manually assembling SMT boards than you can achieve with through hole.
Go to
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and look at the 853A, quartz infrared preheating system. It can be used, in conjunction with a hot air rework station such as the 2738 as a small production assembly unit.
The basic sequence of events is to apply paste to the board where the parts are to go, and manually place the parts using a microscope, or a Mantis viewer. Put the board on the preheater, and set the temperature to slightly above the melting point of the solder paste alloy. Watch the process under the scope until the solder has reflowed on all joints. If one or two are not flowing (usually due to having a lot of heat sink area on the part, connectors are the worst offenders...), apply a little hot air with the hot air rework station.
It is much easier than thru hole because you don't have to prepare the parts in any way, and you don't have to clip leads, ...
I import Aoyue equipment, mostly for my own use, but I do a limited amount of reselling, to make the equipment available at a reasonable cost to small companies, and hobbyists.
There are some interesting new (cheap) systems for doing BGAs too.
Best regards, Spehro Pefhany
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You also need good eyes. I use one of the head mounted magnifying glass things, half to make things bigger and half to let me focus closer.
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The problem with BGAs, is that there is no cheap manner to adequately inspect them. Even the cheaper optical devices are pricey and suffer from significant limitations.
Could possible be done with a pick and place robot. Ie first apply small dots of resin. And then place components. Before reflow. Catch is precision I guess with 0.5 mm pitch.. ;)
I find a "Hoof" tip works much better for SMT devices with many pins. SOIC, TQFP and others. One positions the device as described and solder two pins to keep it in place. Apply some flux, and then with the "hoof" tip full of solder, solder all pins on one side in one sweep. Surface tention and the shape of the tip prevents shorts. If you do end up with a few, it is easy to clean up with Solder wick. With this method it takes under a minute to hand solder a 208 pin TQFP device. One must have PCBs with soldermask though for this method to work.
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