Design for Manufacturability (DFM): Use Surface Mount Components (SMT) - Part 3 of Many

March 26, 2013 Chris Denney

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."

In my first article discussing the importance of using SMT components instead of thru-hole components I mentioned that there are exceptions. The most obvious and important exception is any component that is going to experience a lot of external force. Generally, these are any type of connector where the user will be plugging and unplugging cables often. The amount of force that these connectors experience can be pretty light. But what happens is, overtime, all of those forces stack up and cause the solder joints to weaken. Eventually, those solder joints, or the copper pads that they're connected to, will fracture and you will be left with a broken product.

But connector designers have become wise to this. A lot of modern SMT connectors are coming with tooling pins that are inserted into the board, without solder, or massive leads that are soldered to equally massive copper pads, that can help direct some of the brunt of the force away from the fragile solder joints and copper pads.

As you can see in this picture, there are is a huge contact area on the edges of these D-Sub connectors. These connectors are rated for over 400 cycles. It is very rare for any connector to see that many cycles (except for cell phone connectors which may see as many as 1,000 cycles in its lifetime and they still use SMT connectors). This component was placed automatically with a machine and soldered the same way as all of the other surface mount components on this board. This takes far less time for us than any thru-hole equivalent, and ultimately saved our customer a lot of money.

So, even when it seems like a thru-hole component is absolutely necessary, please consider the alternative. It may save you a lot of money too.

As always, if you have any questions, feel free to send me an email at cdenney@worthingtonassembly.com or follow me on Twitter @WAssembly.

Design for Manufacturability (DFM): Use Surface Mount Components (SMT) - Part 2 of Many

March 25, 2013 Chris Denney

"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.

Design for Manufacturability (DFM): Use Surface Mount Components (SMT) - Part 1 of Many

March 22, 2013 Chris Denney

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. Surface Mount Technology (SMT). The single greatest thing to happen to the manufacturability of electronics since the printed circuit board itself. Rule number 1 of DFM for electronic assemblies

"Whenever possible, use surface mount components instead of thru-hole components."

There are exceptions of course, but generally speaking surface mount components are almost always easier to assemble than thru-hole components. Primarily, this is because of the equipment that most electronics manufacturers employ. Even if your contract manufacturer has fully automated thru-hole equipment, it's likely still easier for them to assemble your design using surface mount components than it is thru-hole components. Today, the fastest SMT machines can pick and place components as fast as 120,000 times per hour. The fastest thru-hole machines still pale in comparison at 26,000 components per hour, and thats only for axial components. Radials are even slower to assemble at 22,000 components per hour.

Remember, time is money when it comes to assembly work. Your manufacturer is charging you for their time. So if he can assemble your board at 120,000 CPH instead of 22,000 CPH, he's going to be able to deliver your product sooner and you'll be saving money.

But placing/inserting the components is only half the battle. You still need to solder it. With surface mount components, all of the soldering is done automatically using solder paste and a reflow oven. Thru-hole components need to either be wave soldered (if designed properly), selectively soldered (if designed poorly), or *gasp* hand soldered (when you really just didn't even think about manufacturability). Talk about taking a long time. Thru-hole soldering is not as easy as it might seem. Yeah one or two joints here or there can be pretty easy. But to solder thousands of solder joints by hand, consistently, year after year, takes a special person with a lot of skill and experience. And those people don't come cheap. Machines on the other hand, while the initial investment is high, are very cheap compared to a competent soldering technician. Time is money.

As always, if you have any questions, feel free to send me an email at cdenney@worthingtonassembly.com or follow me on Twitter @WAssembly.