Benchtop SMT- first try!

[Oznog]

I have a board I had to design the LTC2418 onto, which is a 28 pin SSOP with 0.025" pin spacing- very fine. I've done 8 pin SMTs with the coarser pitch successfully with soldering iron before, but this looked impossible.

So I tried Zephyrtronics SMT paste. Ran a tiny bead, preheated the kitchen oven to 320 deg and put it in. It needs to get over 300 to make the flux run before soldering, but I was instructed in no uncertain terms not to do this with a soldering iron as it had to be done slowly (slowly warmed and held for 60 sec) or it would spatter and behave badly.

Well, my IR thermometer showed it was having trouble getting up there so I ran the oven to 350, and it soon got over 300 and I pulled it out before it could get hotter.

I immediately took it to my soldering station and used a blunt soldering tip, with all the solder wiped off, dragged it across the pins. Things kinda worked like "magic" after that. I thought I'd used too much because I saw several bridges, but dragged again and it finished balling into each individual lead/pad or onto the iron. Under a magnifier, all looks well.

What was I afraid of? Oh yeah... ruining my only prototype manufactured PCB I'd spent major $$ and waited weeks for, and a $15 ADC chip, and still not knowing how to do it. But such things didn't happen and I feel, well, empowered.

 

[Exo]

Yeah, smd devices are scary at first, but once you get the hang of it you won't be using those ugly trough hole devices anymore :lol:

I just use a small tip soldering iron , smallest i've done was a TSSOP package

 

[bmcculla]

The trick to fine pitch SMD is solder wick. You csn use you iron to glob tons of solder on untill all the pins have been soldered to their pads - don't worry about bridging, use as much solder as required. When the whole chip is soldered down go back with solder wick and wick away the extra solder. It works like magic and gives you really great looking results - I had a guy who was giving a demo on profesional level soldering devices think my hand soldered boards were reflow soldered.

If your looking for a quick way to do a bunch of boards PCBExpress will make laser machined solder stencils. You can use them to put down solder paste and then reflow your boards in a toaster oven.

Brent