Surface mount VS Through-hole comparison
2006-04-13 by Robert Hedan
This is for Chris and the others that have yet to fiddle with SMD components. http://groups.yahoo.com/group/Homebrew_PCBs/files/Surface_Mount/ Files: -------- PCB size SMD.JPG PCB size non-SMD.JPG These pics are to scale (to the best of my limitted graphic abilities). The through-hole circuit is 6" x 6" while the SMD circuit is 3.75" x 3.75". Note that the through-hole circuit is single-sided and the SMD is double-sided. I used 1206 size SMD components, 0805 are even smaller but also harder to manipulate if you have a shaky hand like me. Your breath can move 0805 components easily. Both PCBs are different generations of the same circuit; the through-hole version uses a PIC 16F877 while the SMD version uses dual MCP23016 I/O expanders. This circuit receives a signal from a driver board and triggers a keystroke on a personal computer. That piggy-backed green circuit is hacked from a HP USB keyboard. I sprayed clear paint to protect the silkscreen on the through-hole circuit. I had used Pulsar white transfer paper with mild results, the lettering easily came off. On the SMD circuit I sprayed engine block paint and had masked all the pads with ordinary clear adhesive tape. Then I applied the silkscreen using Pulsar toner transfer paper with excellent results. The problems started when I used isopropyl alcohol to clean the rosin, but I'm sure the paint would have been ok if I had cured it as the can suggested (curing = patience = mission impossible). I rely on a headband magnifier for SMD work, they are awesome once you get used to them. I have yet to master the fancy 'single stroke solder technique', I soldered each lead of the SOIC components individually. One trick to hold components in place is to generously wipe rosin on the lands, that stops parts from slipping around. I tack solder one end of a component, then I solder the other end, solder some more the 1st end then I quickly dip the iron into both ends; the liquified solder and surface tension automatically straightens out the component, that's too cool. It takes a bit of practice, but things go smoothly once you get this technique down. I'll work on that 'single stroke across the leads' solder technique some other day. The one time I tried it on 0.5mm pitch leads I got a bridge across 2 leads and it was a royal pain to take it out. I know SOIC are spread further apart, but since I'm not doing massive production batches I don't mind individual soldering the leads, for now. But yeah, by the time I had soldered the 13th MCT6 I was starting to seriously think about practicing that trick. Oh yeah, one last thing, SMD components are priced about the same as their through-hole counter-parts. In some cases they are even cheaper and more readily available. I expect DIP packages to become harder to get over time, so I figured I might as well get used to them now. One added bonus is the lower hole count. I had started making my vias with wire, but now I use the leads on 1/4 watt resistors (or small capacitors, whatever falls under my hand); they are thin, hold in your fingers easily and I've got tons of the stuff. Robert :) [Non-text portions of this message have been removed]