The evolution of the test socket contact design

For many ears now one of the most effective test socket contact designs have been the pogo system especially when it comes to BGA devices. This is a pin design that has been used as far back as in the 1950s when it was first invented by Everett Charles Technologies. During this time, the main use of this was to test the PWBs. However now, with time, the basic design of this has been adapted to complement or to accommodate the various tests of the BGA devices as well.

The initial design

In the beginning there was a “four piece” design element to the pogo pin socket that was also followed up by a design that lowered the number of pieces that were needed to three from four. Both of these offered long contact lives and a comparatively short electrical path of about 5.72mm. These could be configured to cover up a range of sizes and pitches. They could also cover a large range of appliances and are also really steadfast individually.

The four piece designs

The design that had four pieces consisted of two moving probe tips one of which was a spring and one which was a barrel or a tube. This is much longer and also narrower when compared to the three price version of this. When you incorporate this into a socket design, the pins of the four pieced one is compressed into the receptacle or is caught between the two counter drills that are present. Both of the top and the bottom tips will protrude or jut out making the contact between the PWB and the devise that is being tested.

The three piece designs

The three piece design will usually have a top tip, which is also acting as the tube or the barrel of the probe in this case and a movable bottom and top spring. This can be manufactured to be much shorter than the four piece design one but it is also somewhat wider in comparison. The middle section of the barrel area of this design will consist of an annular ring that will keep the probe inside the receptacle. This ring will be captured between the two opposite counter drills so that it stays afloat within the receptacle that it has. This ring however, impeded the use of the three price designs in many of the tight pitch application areas. The way to solve this issue will be to use a really small and screw machine barrel. This is a product that is very challenging to manufacture. It is also a little challenging when it comes to the price in plating because of the small and deep hole that needs to be made in the centre of the barrel.

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