SMT vs. TH

[Sterling Martin]

Hey, curosity has just right now gotten the best of me. I know, it's a bad thing to have happen, and that I should have more self control, but I've got to know if I'm missing out on something by doing all my tinkering with TH components instead of SMT's. Besides the obvious, that being the fact that you need a lot of stuff on a little board, are SMT's in any way superior to TH's? And for the people that use SMT's, do you do any prototyping with SMT's, or is that all done with TH's? Dazed and Confuzed.

[Enzo]

I hate them, others love them, and the sides defend their positions with the fervor of the presidential election. It is amazing how vehemently each position defends itself. Shades of tube vs solid state.<p>No doubt in manufactured good it is where it is at. it works well, is cheap to make. Claims are made as to sm having statisically better reliability. MAybe. The stuff I work on is mostly through hole and is quite reliable too as far as problems related to the board. I encounter the occasional cracked solder on a th part, but I also bump into having to reflow a 100+ leg LSI on a sm board.<p>Personally I am not convinced that sm is easier to breadboard with, but the guys who design on paper and generate a sm board to test their circuit can populate the board easily enough I guess. Of course I tend to work with power circuits and heavier stuff. I haven't spotted any sm 150watt transistors.

[philba]

I was very resistive to SMDs for a long time. It was more a fear of the unknown than anything else. So, I screwed up my courage (not much else left to screw up) and tried it. It turns out to be pretty easy to do. In fact, in many cases, I find SMDs easier than TH. For example, 1206 resistors and caps are a snap to solder on. I can do them faster than TH equivalents. SOICs (50 mil pitch ICs) take only a little more care than DIPs but once you get the hang of it (after the first one!), you'll find it goes pretty fast. more dense ICs are a bit tricky but are quite doable. My investment in equipment? None, I use my hakko solder station with a normal sized tip. I am going to get a hot air station but that's so I can prototype with an expensive part and then pull it off an place it on the final board. I'll do reflow soldering with it as well.<p>Advantages of SMDs:
- no lead forming/bending
- no holes to drill (if you make your own PCBs)
- no leads - better for high freq work
- many newer parts are only SMDs, no THs
- SMD parts are often cheaper
- if you are having boards assembled, SMD parts are cheaper (easier to automate).
- easier to remove (with hot air, especially) and less damaging to traces<p>Some disadvantages.
- easy to lose. there are 3 phototransistors, and a bunch of resistors on on my floor. somewhere... the PTs only cost $.21 so no big.
- some parts are hard to see the orientation. The above mentioned PTs are a bitch to figure out which end is the emitter. even with a 10X loup.
- positioning does require some steadiness. I've found little tricks to help me.<p>For prototyping, I keep a stock of TH components and will breadboard with them but there are a number of techniques for BBing with SMDs. You can get little SOIC, TSSOP, etc adaptor boards that have 100 mil pitch pins for use in solderless BBs. I make my own breadboard PCBs as well. <p>Its basically gravity, you can fight it but its a losing battle.<p>If a 52 year old guy with lousy eyesight and marginally steady hands can do it, just about anyone can.<p>Phil<p>[ February 10, 2005: Message edited by: philba ]</p>

[Sterling Martin]

Good comments! I have been working with TH components. Until one fateful day I needed a such and such A/D convertor. I just up and ordered one, along with some other stuff, from Digikey. The specs said that my A/D convertor was a SMT. OK. No problem, I thought. A surface mount is a surface mount, right? Well, I was shocked when I found my convertor, as it's packaged in a SSOP package! I haven't touched the thing yet, as I'm avoiding the thing like it was the plague itself!

[philba]

Look at this page from digikey<p>You will find an adaptor for almost any case style out there. Though, anything over about 44 leads would be problematic.<p>Soldering dense ICs like ssops is suprisingly easy. The trick is to use liquid flux and solderwick. What I do is tack the IC in place via two corner pins. Flux the pads and then tin two pads on opposite corners of the ICs PCB location. Holding the IC in place with tweezers or a hemostat, touch one corner pin with the soldering iron and then the other corner. <p>Now the IC is held in place. Load up the soldering iron's tip with solder and then drag it along the pins at a rate that is just slow enough to heat the pins and flow the solder. Leave the two tacked pins until last. You may need to replenish the solder on the tip. Don't worry about bridges until you are done with all the pins. Then take solder wick and your iron and soak up the excess. <p>You will be pleasantly suprised at how professional it looks. Interestingly, the larger the iron's tip, the more solder you can load up on it and the faster the work goes. This is the same technique I use for SOICs but they almost never bridge.<p>[ February 11, 2005: Message edited by: philba ]</p>

[Dean Huster]

Phil, the "no holes to drill" advantage of SMD is not really true except for us experimenters. For manufacturers to get the true density that SMD can have, they have to use multilayer boards and vias out the wazoo, something that we cannot do at home. I think that the subminiaturization that hobbyist SMT builders gain is strictly because of the smaller components.<p>It's still easier to breadboard with thru-hole technology. To do it with SMT does require the adaptors ($$$) and it takes time to mount the devices. Unless you have the bucks to allow one adaptor per device, you have to also unmount the SMT and remount others and pretty soon, the adaptor is shot.<p>HOWEVER, there's no reason at all that you can't make your own adaptors and keep the SMT device mounted on it forever. Simply buy the little 8-, 14- or 16-pin DIP headers, make a little adaptor board that'll slip right between the solder forks and you're home almost free compared to the cost of commercial adaptors. Normally, you'll only need this for SMT ICs that you can't (or don't want to) get in thru-hole packages. If you don't want to opt for the DIP header, just make the adaptor board wider add holes on the edges in the proper 0.3" x 0.1" format and drop in brass straight pins that get clipped off. Or use the heavier and thicker square-pin header strips for the pins.<p>Oh, and I'm not much for SMT stuff. (1) I have thousands upon thousands of thru-hole stuff, so if I want to use SMT, I have to order most of it even though I have a good collection of Rs, Cs, ICs, etc. in SMT; (2) as mentioned above, it's more difficult to breadboard; (3) SMT is one of the things that's making electronics non-repairable, not in the sense that it can't be done, but in the sense that it's not cost-effective to do so -- I don't like a throw-away society, which is exactly what we've become, and I'm not even a "greenie tree-hugger".<p>Dean

[philba]

My whole point of was about the hobbiest. I make 2 layer boards at home and I can pretty well get 1/3 or less holes, including vias, by going to SMT. But when manufacturing, SMDs are much easier and cheaper. When I've look into get boards assembled, the price differential is suprisingly high for TH components. Pick and place + reflow is much much cheaper.<p>I dont disagree that TH is easier to prototype with and certainly didn't say that. I make my own prototyping adaptors and they cost me almost nothing but surfboards aren't *that* expensive. Plus, like I said earlier, there are an increasingly larger percentage of parts that never ship in a TH package. <p>Its like gravity - not going away. People can choose to ignore it but then there are plenty of products they are missing out on.<p>[ February 12, 2005: Message edited by: philba ]</p>