Common Failures with Membrane Switches and Solutions

Now, membrane switches are widely used in many industries, including industrial control, home appliances, medical devices, and consumer electronics. While there are many failures with membrane switches when you use them, understanding these common problems and their solutions can help you quickly restore functionality, minimize downtime, and extend the life of your product. 

1. Poor Touch Sensitivity or No Response

There are two situations: no keypads working and Single or Multiple Keypads Not Working.

Symptoms:

When users press the membrane switch button, they either do not receive the expected feedback or the button fails to respond, preventing the system from operating properly.

Situation I: no keypads working

This is the most critical failure, indicating a problem with the common part of the circuit.

Possible Causes:

• Loose Tail Connection: The FPC (Flexible Printed Circuit) or zebra connector is loose, oxidized, or not properly seated in the main PCB's header.

• Circuit Break: The flexible tail or silver traces have fractured, often at a sharp bend or the root due to repeated stress.

• Power/Signal Issue: The main control board is not providing the correct operating voltage to the membrane switch.

• Severe Short Circuit: Internal contamination or silver migration has caused a major short, pulling down the signal.

Solutions:

• Check the Connection: First, disconnect and firmly reconnect the membrane tail to the main PCB. Look for any oxidation on the contacts and clean them with a soft eraser if necessary.

• Measure Voltage: Use a multimeter to check if the correct voltage (e.g., 3.3V or 5V) is reaching the membrane switch from the main board.

• Check for Continuity: Use a multimeter to test the continuity of the traces, especially the common power (VCC) and ground (GND) lines, to find any breaks.

• Swap Test: Replace the suspected membrane switch with a known-good unit. If it works, you've confirmed the switch is faulty and needs repair or replacement.

Situation II: Single or Multiple Keypads Not Working(Others Work Fine)

This is the most frequent issue, localized to specific key circuits.

Possible Causes:

• Dirty/Oxidized Contacts: Dust, oil, or an oxide layer has built up on the carbon/silver ink contacts, creating high resistance.

• Physical Damage:

  • Worn-out Contacts: The carbon pill on the top layer has worn away from heavy use.

  • Broken Trace: The specific silver trace for that key has developed a micro-crack.

• Silver Migration: In humid environments, silver ions can migrate between adjacent traces, forming a conductive bridge (dendrites) and causing shorts or signal leakage.

• Faulty Dome (Metal Snap Dome): If used, the metal dome has lost its springiness or become oxidized.

Solutions:

• Clean the Contacts: If accessible, carefully open the switch and gently clean the top and bottom contacts with a cotton swab dipped in high-purity isopropyl alcohol (IPA).

• Replace the Dome: For metal dome switches, simply replacing the dome for the faulty key often solves the problem.

• Circuit Repair:

  • For Open Circuits: Carefully bridge the broken trace using a fine-tip applicator and conductive silver epoxy.

  • For Short Circuits (Silver Migration): Gently scrape away the migrated material and apply a thin layer of insulating coating (e.g., epoxy) to prevent recurrence.

• Increase Actuation Force (Temporary Fix): Place a small piece of double-sided tape on the back of the top layer (away from the contact) to increase the dome's pre-load pressure.

3. Air Bubbles or Wrinkles

Symptoms:

During use, the membrane switch develops air bubbles or wrinkles, affecting the appearance and touch sensitivity, and potentially leading to poor electrical contact.

Possible Causes:

• Material Defects: The membrane material may have defects, leading to the formation of bubbles, or air may not have been adequately removed during manufacturing.
• Environmental Factors: Changes in temperature and humidity during production can cause the material to shrink or expand, forming bubbles or wrinkles.
• Improper Storage: If the membrane switches are stored improperly, such as being exposed to moisture or high temperatures, they can develop bubbles or wrinkles.

Solutions:

• Optimize Production Environment: Ensure proper temperature and humidity control in the production environment to avoid external factors affecting the membrane layer. Use advanced processes and equipment to ensure the membrane’s flatness.
• Select Suitable Materials: Use high-quality, environmentally stable membrane materials that reduce the likelihood of bubble formation.
• Improve Storage Conditions: Store the membrane switches in a dry, temperature-stable environment, avoiding exposure to high temperatures or humidity.

4. Key Ghosting or Crosstalk

Symptoms:

Pressing one key triggers another key on the same row or column (common in matrix circuits).

Possible Causes:

• Silver Migration: The primary cause, leading to low insulation resistance between adjacent row/column lines.

• Poor Circuit Layout: Traces running parallel for too long at a close distance are susceptible to leakage current.

• Internal Moisture: Humidity inside the layers drastically reduces insulation resistance.

Solutions:

• Isolate and Clean: Identify the shorted traces, clean the area thoroughly, and apply a reliable insulating sealant.

• Dry it Out: For switches exposed to moisture, a low-temperature bake (e.g., a few hours at 50°C/122°F) can help. Ensure the switch laminate is fully sealed.

• Design Revision: The ultimate fix is to redesign the circuit with wider trace spacing or incorporate blocking diodes in the matrix.