Sunday, July 10, 2011

Using SMT chips on TTH breadboard


I usually make a custom PCB for my electronic projects. Throughout development the PCB, however, changes several times. Making a custom PCB at each stage is not practical for several reasons including price, long waiting times between versions and being very wasteful. For all these reasons I use a test board/breadboard/prototype board that can be changed easily and instantly before development reaches a final stage.

The finished blob is comfortable seated in a test board.


There is one problem with this approach: test boards are designed to take TTH (through the hole) components and cannot take SMT parts. I usually use SMT parts to make my PCBs as small as possible, so the solution for me so far has been to buy both SMT and TTH versions of a chip, use one for development and the other for the final product. This has been working for me for quite some time, but now I am in a situation where the manufacturer doesn't make TTH version of a particular chip.

In this case I was using the 8 pin SOIC version of MAX6675.


To overcome this problem I came up with a quick and dirty solution: I solder thin copper wires to each of the pins of the chip and connect them to some pin headers that are soldered in a piece of breadboard. The advantage of this method is that it can be done to almost any chip, doesn't require special resources and creates a very durable design that - so far - seems indestructible. The only disadvantage is that the chip that is "converted" into TTH cannot be used for anything else afterwards. This is not a big problem for me as I always buy more parts than I actually need (just in case I mess up something...).

Materials needed

A piece of solder-in prototype board
Front/Component side of the prototype board
Straight type pin header - cut to match the number of pins of the chip

I also used the following items:
  • AWG 35 laminated copper wire
  • soldering iron/solder
  • hot glue
  • sharp knife of saw to cut the breadboard to size

Build steps

  1. Pre-solder all the pins of the chip
  2. Solder about 2-3 cm (1 inch) insulated copper cable to each pin
  3. Cut a piece of breadboard to size and solder in the required number of pin headers
  4. Solder each copper wire to its respective pin header
  5. Important: test and double check if you have soldered everything correctly with a multimeter (check for shorts and breaks everywhere because after the next step it will not be possible to change anything)
  6. Fill the gap between the chip and the breadboard with hot glue
  7. When the assembly cools down it's ready for use in a standard breadboard
All connections soldered and tested
Hot glue holds the assembly together - no going back from here!