Key failure is one of the most frequent faults in membrane switches,which directly affects the operation of industrial equipment,medical devices,and household appliances.This summary sorts out the main failure types,root causes,and targeted troubleshooting solutions for membrane switch keys.
1.Common Key Failure Types and Corresponding Causes
Type 1:Key No Response(Press No Signal Output)
This is the most common failure,and the causes are mainly divided into 4 categories:
Circuit Layer Damage
Physical wear:Long-term key presses cause the conductive silver paste on the circuit layer to wear off,resulting in circuit disconnection.
Corrosion:In humid,acidic,or alkaline environments,the conductive silver paste reacts chemically,leading to circuit oxidation and open circuits.
Manufacturing defects:Uneven printing of conductive silver paste,pinholes in the circuit,or poor connection between the circuit and the connector during production.
Adhesive Layer Degradation
The adhesive layer between the upper and lower circuit layers ages,hardens,or delaminates,causing the upper circuit(contact point)to fail to touch the lower circuit when pressed.
Low-quality adhesive absorbs moisture and swells,separating the circuit layers and losing the conduction function.
Foreign Matter Infiltration
Dust,oil,or liquid penetrates the internal structure of the membrane switch through gaps at the edges,accumulating at the key contact points and preventing circuit contact.
Residual adhesive or debris during die-cutting and bonding remains in the contact area,blocking the conductive path.
Connector Fault
The connection between the membrane switch's tail cable and the PCB board is loose,or the pins of the connector are oxidized,resulting in poor contact of the circuit.
The tail cable is folded or pulled excessively during installation,causing internal circuit breakage.
Type 2:Key False Trigger(Automatic Signal Output Without Pressing)
Circuit Short Circuit
Conductive silver paste on adjacent circuits overflows during printing,causing a short circuit between the key circuit and the ground wire.
Moisture or conductive dust forms a conductive bridge between the circuits,leading to continuous signal output.
Deformation of the Top Panel
The top PET/PC panel is deformed by extrusion or high temperature,causing the upper circuit contact point to be in a long-term contact state with the lower circuit.
Excessive Elasticity of the Spacer Layer
The spacer layer(dielectric layer)between the upper and lower circuits is too thin or loses elasticity,failing to separate the two circuits effectively when the key is not pressed.
Type 3:Key Response Intermittent(Unstable Signal Output)
Poor Contact of the Contact Point
The conductive silver paste at the key contact point is partially worn,and the circuit is connected only when pressed at a specific angle.
Oxidation film forms on the surface of the contact point,increasing contact resistance and leading to unstable signal transmission.
Loose Adhesive Bonding
Partial delamination of the adhesive layer causes the contact between the upper and lower circuits to be unstable when the key is pressed.
Voltage Fluctuation
The working voltage of the membrane switch is lower than the rated value,resulting in insufficient driving current and intermittent signal output.
2.Standard Troubleshooting Methods for Key Failure
Step 1:Preliminary Visual Inspection(No Need for Disassembly)
Check the appearance of the membrane switch:Whether the top panel is deformed,scratched,or has obvious liquid stains;whether the edge sealing is intact,and whether there is delamination or warping.
Check the connector:Whether the tail cable is loose,folded,or pulled;whether the connector pins are oxidized(black or green rust).
Manual test:Press the faulty key multiple times to feel whether the pressing force is consistent,and whether there is a sense of"blocking"or"sagging".
Step 2:Electrical Performance Testing(With Multimeter)
Resistance Test for No-Response Key
Set the multimeter to the resistance gear(Ω).Touch the two pins of the connector corresponding to the faulty key with the test leads.
When the key is not pressed,the resistance should be infinite;when pressed,the resistance should be<100Ω.
If the resistance is infinite both when pressed and not pressed→The circuit is open(focus on checking the contact point and tail cable).
If the resistance is always<100Ω→The circuit is short-circuited(focus on checking for foreign matter infiltration or silver paste overflow).
Voltage Test for Intermittent Response Key
Power on the equipment,set the multimeter to the DC voltage gear,and test the voltage at the connector pins corresponding to the faulty key.
When the key is pressed,the voltage should switch stably between the rated value and 0 V;if the voltage fluctuates→The contact point is oxidized or the connector is in poor contact.