Re: [sdiy] moving to SMD/SMT

[Roman]

hi,

>Anybody here doing much with SMT? I'm looking to make the jump. Many
>ICs are only available in SOIC and TSSOP packages, as we all know. I
>like the idea of building small stuff, though, and those discrete SMDs
>are so small. (Widdle baby weesistors, awww, so cute! ;-)

there are probably lots of people doing SMT, and it's getting more popular. I've been doing that for couple of years.
Yes, they are so cute, and look even cuter when soldered to PCB.

>
>So, what kind of equipment do I need?

basicaly the tolls you use for thru-hole. Teperature controlled soldering iron, 0.8-1mm tip size is enough for most of the stuff. 
If you want to use TSSOP an smaller, you'd need another type of tip, that has little hollow at tip's tip ;) Secure the chip at its corners, put some solder into the hollow and smear it along one side of the chip. It's quick and looks pro.
BTW, I've been known from soldering 0603 with bulky transformer-type soldering gun. I still do that when I don't want to heat my solder for single joint, or when I want to desolder 2-leads component using both - soldering iron, and soldering gun.
Soldering tweezers would be nice, but too expensive for just few those times when they would be useull.

Non magnetic tweezers of several kinds, and best if they are titanium, or ceramic (that's a luxury). I use mainly 2 kinds - straight with small tip (0.5mm I guess) and angled with rounded tips that hold round components (MINIMELF) securely. It made me soldering diodes 3 times faster.

Thin solder is most important. The thinner, the better. IMHO best would be smaller in diameter than SOIC lead.

Good lamp and big magnifying glass. There are lamps with the glass, and they would be perfect. I don't use the glass, but I may have to buy it in near future as I turn into old-fart.

It would be nice to have also ESD-safe environment too.


>I've also read about the toaster oven reflow technique. Seems
>interesting, and I suppose that I'll try it, but it won't replace the
>need for a more focused soldering method.

I've been thinking about it too. It requires solder paste, that AFAIK has short "best before" period and needs to be kept in the fridge. And it's not an easy task either. There are couple of websites describing home-made reflow ovens. Succesfull ones.

>And since SMDs usually go on PC boards, is there anything special to
>keep in mind when making PCBs?

thermal resistance.
don't make SMD pad as part of ground plane or another thick track. Always make short fraction of thinner track that leads to the component's pad. It would be a lot easier to solder and won't kill the component from long soldering heat.
And if your design is dense, it maybe difficult to get the solder tip to some places because of other components crowd.

>
>Any other tips, warnings, or links?

decide up front on one size of components. I'd suggest 0805. They are easily to handle and not so large and bulky as 1206. It's easier to find 1% and better resistors in that size (although it's getting easier now in 0603 size), SMT tepcos are available cheap in this size. Use larger size only when power rating needed is bigger.
Review all your schematics and ideas you want to do and make list of purchase. Buy 100 of each value, 200-300 of more frequently used ones. And try to find 1% TC50 resistors. They are not so rare and cheap.
Parts storage is another issue. I use small round plastic containers with caps purchased in medical shop (1cm diameter, 4cm height). All held in square foam keep all of my passive components in one place.

Roman