Much has been written about the advantages for various types of mounting component methods for large scale production and final applications as reflected in the References for this blog. However, there is very little written about how prototype boards are influenced.
Large scale production differs from prototyping in many ways. That which is learned during the prototyping stage makes it into the final production version. In other words, the design is pretty much complete by the time one has a production version. Prototyping however can be a different story. Even with beforehand software analysis with SPICE or other evaluation programs, there still needs to be a certain amount of breadboard evaluation and adjustment each of which requires access to leads and the ability to unmount and remount new versions of components. Herein lays the problem. Although many of todayís surface mount packages (or Surface Mount Devices ĖSMDs) have shrunk in size, they are a nightmare to unsolder and re-solder. Also, many of the leads are very close together which makes probing and soldering them difficult. Finally, they donít fit well into a pluggable prototyping board the way leaded components do. So whatís one to do?
The answer to this is quite simple, lay your board out with through-hole components, if you can find them that is. Many of the newer components arenít available in through-hole packages. However, you can often find fully completed demo boards to use. It all depends on whether the application the demo board is intended for fits as a block in your block diagram. If you need to work down at the component level, it might be difficult lifting leads or accessing traces in a multi-level printed circuit board (PCB) when ordering a demo board that features a desired component. Still, the demo board movement can be your friend when prototyping as it often offers a ready-made circuit.
One problem with soldering through-hole components to boards is that the soldering is the mounting method. If the component fries, which is often the case with power components, there is work involved in removing it. In this instance, it might be best to use a socket which your solder to the board. Thankfully, TO-220 sockets have been reduced in size over the years and are no longer the space hogging monstrosities they once were as shown in the photos.
Finally, a Space-Friendly TO-220 Design
TO-220 and other packages have spacing and lead size issues when plugging them into a protoboard. Also, protoboard current and voltage ratings might not allow for the evaluation of higher power circuits. Thatís when itís a good idea to use a prototype board that allows you to solder components rather than the pluggable models. A representative example of pluggable and solderable prototype boards are shown.
Abra Electronics has an example of a pluggable board
Pluggable Protoboards are Convenient Yet They Do Introduce Parasitics
Through-Hole, Solderable Prototype Boards are Often Conductive on Both Sides
Through-hole, solderable prototype boards are often conductive on both sides which gives more options for running signals while creating a potential for objects to short the back side while lying on the bench. Use of standoffs or placement on an insulated surface is recommended. Be sure to remove and leads and wire debris that could short the circuit as well.
Like TO-220s, sockets exist for many leaded Dual In-line Packages (DIPs). Some sockets have solid round pins whereas others have the flat leads. I prefer the flat leads when mounting to a solderable prototype board that lacks through-holes. That way, I can bend the leads outward and actually solder to two pads on the board. The round pins donít bend as easily as the flat ones.
DIP Socket with Round Pins
DIP Sockets with Flat Pins
It is possible to find SMD package sockets that can be soldered in place while accommodating a surface mount package. As shown, these packages can be a bit bulky.
Surface Mount Package Sockets are Rather Bulky
One suggestion when ordering sockets. Order more than you need. Youíve already paid shipping and will spend less time hunting them down for future projects.
Prototyping a circuit is often a laborious task that can be made easier with a little forethought. Various types of options are available based on whether the technology used is through-hole versus surface mount. Contract manufacturers have eased the pain of protoyping with fast board turns and available software packages. Still, their focus is on high run rate completed boards. Sometimes it can be quicker and result in a more flexible test bed when opting for the old fashioned way of using through-hole components.
- Through-Hole vs. Surface Mount .
- ďThe Difference Between Through Hole And Surface Mounted TechnologyĒ, Contract Electronics Manufacturing and PCB Assembly Blog, Posted by Laura Austin on Thu, Nov 29, 2012 @ 07:00 AM
- ďWho Comes Out On Top Between SMT vs. Through-Hole Mounting?Ē, Contract Electronics Manufacturing and PCB Assembly Blog, Posted by Matthew Turpin on Thu, Jul 24, 2014 @ 08:05 AM,.