This is just one article in a series of articles discussing design for manufacturability for electronic assemblies. As a contract manufacturer we see every possible design decision you can imagine. We know what works, and we know what doesn't. We're happy to look at your assembly for any manufacturability concerns, whether we're building the assembly or not. Remember, rule number 1 of DFM for electronic assemblies
"Whenever possible, use surface mount components instead of thru-hole components."
The number one reason we tend to hear here at Worthington Assembly, about why designers don't want to design their boards with SMT components is that if the designer needs to remove components himself then SMT components are too difficult to work with. This also happens to be the worst reason in my opinion for choosing thru-hole components. SMT components are actually far easier to work on with just a soldering iron than thru-hole components. When a thru-hole component is well soldered, you're going to have a really hard time remove it with just a soldering iron. You have to heat up one leg, grab it with a pair of pliers, pull the lead through the hole, and pray that you don't damage the barrel while doing it. Then you need to do the same to the other side. SMT components however, are quite simple to remove with a soldering iron. We call it the old "blob of solder" removal method. Take your soldering iron, take your solder wire, blob a whole bunch of it on the tip of the iron, set that blob onto of your SMT resistor and then just lift up. The surface tension from the solder will cause the SMT resistor to come right up with the tip of the soldering iron. It could not be any easier.
Now, there's another reason designers may choose thru-hole components instead of SMT components that is related to what we just discussed. This is the thought that it's easier to assemble a thru-hole board by hand than it is to assemble an SMT board by hand. This can be true. Sometimes it is easier to procure material and handle that material than it is to handle the same SMT material. If you're building just one board, and only one board forever, then this is probably ok. DFM shouldn't even be considered in that case. But if you expect to sell even a few dozen pieces of your design (or millions!) then you will definitely want to start with an SMT design from the beginning. And I think you will be surprised. With the right tools, like a tweezer soldering iron, SMT components can be soldered really easily.
As always, if you have any questions, feel free to send me an email at cdenney@worthingtonassembly.com or follow me on Twitter @WAssembly.