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How can I make a Flat Flex Cable (FFC) Zero Insertion Force (ZIF) connector resistant to environmental contamination?

Background/Assumptions:

I have a microwave over my stove. Every few months, the keypad begins to malfunction and register key presses without human interference. Naturally, it's one of the buttons that will start the microwave. After a while, the keypad will become non-responsive. The keypad in this unit is a sealed membrane unit with a single FFC. Nothing in the keypad requires active electronics, and the number of contacts and buttons) strongly suggests a standard sampled keypad switch matrix.

I'm pretty sure a row line adjacent to a column line is getting a low enough resistance to register as a button press. Removing the FFC from the ZIF connector and re-inserting it will fix the problem for about a day. Cleaning the FFC and flushing the ZIF connector with isopropyl alchohol will fix the problem for a few months. Considering that the electronics compartment isn't well sealed, I believe steam and other cooking byproducts are making their way into the ZIF connector and causing measurable leakage between pins.

The FFC termination is single-sided with a pitch of about 1.25mm/50 mil. The microwave is a Samsung, but I don't think that's relevant to the solution.


FFC ZIF Removed FFC_ZIF_Inserted

How can I improve the environmental resistance of a FFC connection? Looking at the connector, it seems like there is an unsealed path on both the top and bottom of the connector. My priorities (in order) are:

  1. Don't buy a new microwave - the old one works*
  2. Make the fix permanent so I'm not constantly disassembling the microwave
  3. Don't make the connection permanent (e.g. soldering the FFC to the board)
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  • \$\begingroup\$ Possibly seal the cable-connector interface with self-vulcanizing tape? 3M and others make rubber and also silicone varieties. \$\endgroup\$ – AlmostDone May 5 '18 at 15:05
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Hewlett Packard instruments in the 70's used to specify maintenance for their gold plated card edge fingers using only Pink Pearl©® Rubber erasers (lol).

Isoprop. does wonders with a Pink Pearl and the contamination could also include oil and water vapours which are excellent electrical insulators.

But the ZIF socket has a problem if the retention force is zero and does not have a "gas-tight" seal because even non-24 caret gold is still prone to some oxidation with high temp and humidity.

Examine the surface under a 10x lens and look for pitting and lubricate and wipe the mating contacts with isoprop and repeated Pink Pearl treatments to the FPC being careful not to leave any shreds inside the socket.

Then as @Almostdone has suggested use Plumber's waterproof stretch tape black tape for moisture leaks and wrap around the socket with minimal stress on the FPC yet sealing the clean surface with finger pressure after wraps.

The alternative is Silicone which still has moisture ingress but slows it down and it may block greasy water vapours but may be harder to repair.

That should last you more than a year. I wonder if Korean's use this microwave for Kimchi style cooking? If so, Samsung ought to have a better Quality Reliability Test Engineers.

enter image description here

The other possibility is excess pressure on membrane carbon contacts has smeared the carbon to make certain buttons like "Start" wear out faster.

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  • \$\begingroup\$ Good suggestions on cleaning. Another thought on sealing might be peelable solder mask. \$\endgroup\$ – AlmostDone May 5 '18 at 15:30
  • \$\begingroup\$ Yes or Kapton Tape like the roll I got from Banggood \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 May 5 '18 at 15:33
  • \$\begingroup\$ Would Kapton tape conform to the irregular shapes and angles where cable meets connector? \$\endgroup\$ – AlmostDone May 5 '18 at 15:42
  • \$\begingroup\$ Depends on thickness but in CM shops I was in yes. They used it to protect certain parts going thru wave soldering. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 May 5 '18 at 15:53
  • \$\begingroup\$ None of the buttons feel work out, and the button that gets "pressed" is one we never use. The sealing tape sounds like a good idea, I'll give that a shot. \$\endgroup\$ – W5VO May 5 '18 at 17:27

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