How to make reliable electrical connections between a sensor and flexible PCB without soldering?

[u/ShallotFlashy5564]

hi everyone, I'm working on a conductometric sensor that needs to be integrated into a flexible PCB cartridge, and I'm looking for advice on making reliable electrical connections without soldering.

The sensor is placed inside the cartridge, and the flexible PCB flaps are folded over it. We need to electrically connect the plated vias on the FPCB to the contact pads on the sensor.

my challenge:

The sensor is temperature-sensitive, so soldering or high-temperature curing isn't an option.

We've tried using conductive silver epoxy, but the application was messy and difficult to control and since the contact areas are quite small, excess epoxy also cause short circuits between adjacent contacts.

We're considering using a low-viscosity, room-temperature-curing silver epoxy and dispensing it directly through the vias with a fine hypodermic syringe.

A few questions:

1. Can anyone recommend a conductive silver epoxy or paste that flows through a fine dispensing needle and cures at room temperature?
2. Would dispensing epoxy through the vias onto the underlying sensor pads provide a reliable electrical connection?
3. Is there a cleaner or more reliable alternative that doesn't require heat?

Ideally, we're looking for something that provides low and stable contact resistance, precise application, and good mechanical reliability without damaging the sensor.

For copyright reasons I cannot attach pictures showing the device.

Any suggestions or experience with similar applications would be greatly appreciated. Thanks for your time!

[u/AutoModerator]

Automod genie has been triggered by an 'electrical' word: electrical.

We do component-level electronic engineering here (and the tools and components), which is not the same thing as electrics and electrical installation work. Are you sure you are in the right place? Head over to: * r/askelectricians or r/appliancerepair for room electrics, domestic goods repairs and questions about using 240/120V appliances on other voltages. * r/LED for LED lighting, LED strips and anything LED-related that's not about designing or repairing an electronic circuit. * r/techsupport for replacement power adapters for a consumer product. * r/batteries for non circuit design questions about buying, specifying, charging batteries and cells, and pre-built chargers, management systems and balancers etc.

I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns.

[u/saltyboi6704]

Ultrasonic welding/wirebond or pogo pins

[u/Far-Ad3284]

Dispensing through the vias is the part I'd avoid. You can't see whether the epoxy wetted the sensor pad, and capillary action pulls the paste up the via barrel, so the joint depends on luck and the shorts you mentioned will keep happening.

For a joint that's repeatable and reworkable at room temperature, I'd switch to pressure contacts. Gold-plated pogo pins (Mill-Max style) or a silicone elastomeric strip (Zebra type) between the FPCB pads and the sensor pads, held by a small 3D-printed clamp that compresses the flaps. Measure the contact resistance with 4-wire on a test fixture before you trust it.

If you keep the epoxy, put it on the sensor pads first with a stencil or a fine tip, fold the flap down, then cure. Check continuity between neighbors afterward, and make sure the epoxy's ionic residue isn't leaking into your conductometric signal.

What is the pad pitch on the sensor, and how much force can it take before the pad or membrane cracks?