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Surface Mount Versus Through Hole, A Retrospect for Prototyping

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 today’s surface mount packages (or Surface Mount Devices –SMDs) 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 don’t fit well into a pluggable prototyping board the way leaded components do. So what’s 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 aren’t 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.

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Finally, a Space-Friendly TO-220 Design

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. That’s when it’s 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

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

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 don’t bend as easily as the flat ones.

DIP Socket with Round Pins

DIP Socket with Round Pins

DIP Sockets with Flat 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

Surface Mount Package Sockets are Rather Bulky

One suggestion when ordering sockets. Order more than you need. You’ve 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.

References

  1. Through-Hole vs. Surface Mount .
  2. The Difference Between Through Hole And Surface Mounted Technology”, Contract Electronics Manufacturing and PCB Assembly Blog, Posted by Laura Austin on Thu, Nov 29, 2012 @ 07:00 AM
  3. Who Comes Out On Top Between SMT vs. Through-Hole Mounting?”, Contract Electronics Manufacturing and PCB Assembly Blog, Posted by Matthew Turpin on Thu, Jul 24, 2014 @ 08:05 AM,.

5 comments on “Surface Mount Versus Through Hole, A Retrospect for Prototyping

  1. Victor Lorenzo
    April 22, 2017

    Nice post, Scott,

    In my case the selection between SMD or TH for prototyping is driven by several things. For slow circuits with just a few components I often used the breadboard, when noise was a concern or for circuits destined to last more than a few minutes I then used a fragment from a protoboard. In some cases a breakout board comes very handy for small SMD packages.

    But in most my current prototypes I go directly to building the PCB in our workshop. The whole process takes in many cases just a couple of hours, including the PCD design. I use one CNC controlled mill (modified BF20L Vario + Mach3). For generating the G-Code from the gerbers I use flatCAM and auto-leveller. It is not difficult to make double sided PCBs this way with track widths down to 0.2mm and isolation of 0.25mm using LPKF 0.2-to-0.5mm bits.

    I modifed flatCAM (it is open-source, written in Python) for optimizing the generated output G-Code. With the original code you often want to modify the ouput g-code to make it safer and faster.

  2. antedeluvian
    April 23, 2017

    A new alternative is the conductive ink printer like the Voltera. I acknowledge that it is pricey for a home/hobby set up, but not so bad if you can treat it as a business acquisition. Watch for my blog the Voltera V-One on embedded.com in May.

  3. antedeluvian
    May 11, 2017

    My blog on the Voltera V-One is now published.

    Road trip to Voltera

  4. Effective-Technical-Writing dot com
    June 27, 2017

    Interesting stuff.  I'll have to try it out.

  5. Effective-Technical-Writing dot com
    June 27, 2017

    It sounds like you have more sophisticated toys than I do.  I was able to generate a provisional patent with wire ties and wire recently.  It can still be done low budget with objects that are just laying around but alas, some of the stuff was bored from my son's RC car parts bin.  It could justify hoarding but then again, how much is too much?

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