improving electrical connectivity of test probe - Page 1
Forum section: electronics / beginners

author: engineheat
author_rank: Frequent Contributor
timestamp: September 12, 2019, 06:09:49 pm
content: Hi,In an automated current testing fixture, the following spring loaded testing probe/pin is used:The material is steel but it's gold plated. The spring force is at most 1.5N but I don't think we are compressing it that much. Anyway, we are getting too much unreliable connections which leads to excessive test failures.A couple of issues I suspect:1. The internal spring mechanism doesn't lead to a reliable connection2. The gold plating wears off and the exposed steel oxidizes on the testing surfaceI want to try to modify it by taking away its internal spring loaded mechanism and directly solder a coil spring of my own. Also, by using a stronger spring, it can help to create a stronger connection, which can help with the oxidization issue.I wonder if it's a good approach to this, and if so, what kind of spring (material) I should get to allow it to be soldered.Thanks

author: MagicSmoker
author_rank: Super Contributor
timestamp: September 12, 2019, 06:23:35 pm
content: Perhaps the problem is the relatively large and flat contact face? Usually pogo pins come to a point, or at least are relatively small in diameter and hemispherical at the end. At any rate, you want the contact area of a pogo pin to be small so that the pressure per unit area is high for a given spring force.

author: engineheat
author_rank: Frequent Contributor
timestamp: September 14, 2019, 06:09:44 pm
content: Actually, the large flat probe surface is fine. The contact that it touches is small, albeit not sharp. There are positional variation with the contacts that needs probing, so the probe need a large surface.thanks

author: Gyro
author_rank: Super Contributor
timestamp: September 14, 2019, 06:26:01 pm
content: If you are dealing with non-sharp contacts then it could be that your problem is down to contamination / flux residue.If you have an alignment variation issue, you would normally tackle it with a larger exposed PCB pad and a sharp probe. The flat probes are really better used where you have a decent contact point on the board (ie. not very often).If you are losing the plating quickly then it sounds as if you have a lot of sideways 'scrubbing' action that you should maybe address in the test jig.Is this actually a PCB application?P.S. You can get more robust pogo pins, eg.https://www.mill-max.com/products/new/spring-loaded-pogo-pins(Harwin do them too)

author: MagicSmoker
author_rank: Super Contributor
timestamp: September 14, 2019, 08:45:17 pm
content: Quote from: engineheat on September 14, 2019, 06:09:44 pmI don't know if you and I are referring to the same contact face... I'm saying the contact face on the pogo pin needs to come to a point or a hemisphere so that a high contact pressure is developed despite a relatively feeble spring force. This will let you use regular HASL pads on the PCB for test points, rather than ENIG or spot gold. If you need a large pad and pogo pin contact area to account for slop/variation then you are doing it wrong. Automated test fixtures should always have a means of positively locating the board with respect to the pogo pin array (aka "bed of nails").

author: Wendy_Preston
author_rank: Contributor
timestamp: October 04, 2019, 07:44:51 am
content: Quote from: Gyro on September 14, 2019, 06:26:01 pmApologies, bit late to the party - here's Harwin's selection:https://www.harwin.com/connectors-hardware/spring-loaded-contacts/https://cdn.harwin.com/pdfs/Harwin_PC_Spring_Loaded_Contacts.pdf