Techniques for Measuring Continuity with Delicate Materials - Page 1
Forum section: electronics / projects

author: epsilon0
author_rank: Newbie
timestamp: August 29, 2023, 01:02:22 pm
content: I have a fine silicon nitride mesh (~5 micron thickness, 100x25 micron spacing), coated with titanium and gold, that is mounted onto a copper substrate using a conductive epoxy. I need to measure/verify the continuity between the copper and the mesh surface without damaging or deforming the mesh.I have successfully measured thin-film coatings on more rigid substrates using EMI gasket material but I think the pressure applied by the gasket will damage the mesh in this case. I'm thinking of using some low force spring contact probes (0.7 ozhttps://www.mouser.com/ProductDetail/Smiths-Interconnect-IDI/QUAD-0J-0-0-WO-WIRE?qs=lqp2fNp7n%252BZQlB2rh4%252BJlg%3D%3D) or even a tantalum wire probe (https://micromanipulator.com/products/accessories/probe-tips/model-7a/) at this point in time.Does anyone have any other recommendations for making delicate but accurate (4-probe Kelvin) resistance/continuity measurements on fine meshes and thin foils?EDIT: Attached a picture for those that are interested.

author: ajb
author_rank: Super Contributor
timestamp: August 29, 2023, 03:38:29 pm
content: Wow, that's an interesting set of requirements, and a neat looking part. What level of precision/accuracy are you looking for, and what sort of resistance are you expecting? Presuming that the mesh is bonded around the whole perimeter, the tricky part with a kelvin measurement is deciding how the force and sense leads would need to be arranged on the mesh to ensure that the contact resistance is properly eliminated. How big a deal that is will depend on the magnitude of the resistances in play.Could you apply a droplet (or two for a kelvin measurement) of a conductive fluid to the mesh/film and use that as an intermediate contact between the probe and the DUT?

author: jmelson
author_rank: Super Contributor
timestamp: August 29, 2023, 04:34:09 pm
content: Just to measure continuity, how about a fine needle and a drop of conductive liquid? Maybe some salty water, put a drop on the mesh, then put the needle into the drop and check continuity. If you actually want a resistance measurement, put a drop on a solid surface that it doesn't wet to and then read the resistance there and compare to the mesh. Then, wash the salt water off the mesh so it doesn't cause corrosion.Jon

author: Marco
author_rank: Super Contributor
timestamp: August 29, 2023, 05:21:34 pm
content: Make a circle out of a single carbon fibre strand from some heating wire or similar and glue it to a probe?

author: bdunham7
author_rank: Super Contributor
timestamp: August 29, 2023, 05:27:30 pm
content: The first thing I thought of was the conductive liquid like everyone else, but how about a cotton swab (Q-Tip) with a bit of gold foil over the end? If the outer layer of your mesh is gold and you use a gold foil, you won't need any force at all to get through oxidiation layers on either component.

author: epsilon0
author_rank: Newbie
timestamp: August 30, 2023, 02:41:52 pm
content: Thanks for the input everyone. I should have specified that the primary goal is to verify DC continuity between the copper and the mesh. This assembly is an electron lens; placed in a vacuum and biased to a few hundred negative volts during operation, while electrons fly through it for 10s of nanoseconds. Having a consistent and constant charge distribution across the mesh is key for our application, and requires verifying that an applied voltage to the copper fixture is the same voltage seen by the mesh over that time frame.I expect the resistance to be no more than a few Ohms per cm, based on similar gold coating measurements on glass substrates.We'll play around with these ideas and report back on how it goes.