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Circuit Board Assembly: Right Kind of Membrane Switch

Circuit Board Assembly: Right Kind of Membrane Switch

May 20, 2021

The use of low-quality membrane switches often leads to performance and construction issues

The typical and conventional keyboard, a low-profile design, carries a circuit board assembly where we imprint the circuit switch. It thereby is a flexible membrane keyboard design for conventional uses. in the design, the manufacturer generally uses silver conductive polymer ink. The sheet where this ink applies is of polyester in nature. Therefore, to separate the two opposing layers of polyester circuits, the manufacturers use a thin layer of the adhesive sheet.

circuit board assembly

At the end of the sheet, however, there is a hole that carries a switch. Now to make the circuit function in a proper manner, one needs to push the membrane by putting pressure on the switch. In this way eventually, the first circuit layer gets deformed with the help of a spacer hole. To provide the circuit with a tactile feel we use polyester material domes i.e., poly-domes.

Common Problems Associated with Membrane Switch

As we know that the circuit board assembly that carries the membrane switch comprises polyester material. Therefore, it is a recommendation to place and install it on some hard and rigid surfaces. It is because the sheet or adhesive layer is not capable enough to support itself independently.

Therefore, we use a common most plate for this supporting purpose is aluminum sheet. It is flat and rigid enough to let the membrane work properly. For this reason, hence, there are extremely large membrane switch keypads that are in wide use in most industrial sectors.

However, there are some common problems relevant to these large-sized membrane mounted-switches on metal surfaces. Some of these problems are performance and contrition integrity issues. These problems are very much visible in less ideal working conditions.

Low-Performance Issues in Membrane Switches

As we have already discussed that the circuit board assembly that carries flexible membrane keypads is generally based on polyester material. This polyester sheet carries a silver conductive ink for connecting paths.

It thereby becomes a common material that is able to carry a physical memory to come back to its natural shape. To make the membrane work there is a need to apply pressure on the switch to open it. similarly, when we apply the pressure again, we close the connection.

The performance of the membrane switch gets affected when we use materials other than polyester. It happens because polyester is the only material to come back to its natural shape. All other materials however fail to come to when we apply pressure on them.

Eventually, polyester becomes the only material that is used universally for membrane keypad application worldwide. There are other acrylic membrane switch keypads also. But all of them carry their specific characteristic.

circuit board assembly

These characteristics specify the performance of the material and its related cost. Some low-performance keypads are common in throw-away applications.

Construction Integrity Issue in Membrane Switches

Even with the best-designed circuit board assembly carrying keypad membrane switches, the chances of problems are very common. These issues are more apparent in designs that have large keypad membrane switches and metal plates.

These construction integrity issues exist because of some technical and natural reasons.  The first and foremost reason for facing the issues is the difference in thermal coefficient.

The thermal coefficient factor of supporting metal plate as well as polyester or adhesive membrane is different. This difference in temperature causes sheer stress between the interface of the acrylic membrane keypad and metal plate.

Issues with Mounted LEDs

When in a membrane switch a common problem surfaces, other issues also appear readily in response to the main problems. The first and foremost issue is the mounted LEDs. As we know that membrane keypads carry surface mount LEDs as well.

However, the appearance of stress, heat, and vibration causes issues in these mounted LEDs. Furthermore, the silver circuits and polyester adhesive materials are not rigid enough to withstand high soldering temperatures. It ultimately affects the LEDs that are connected to silver circuits as well.

It though seems a perfect idea to attach small surface-mount LEDs with silver circuit board using conductive epoxy. However, the issue that affects the performance of the LEDs is that polyester film carries a peel strength which is way harder than what we look for.

This stress and excessive strength cause the disruption as well as dislocation of LEDs connections. It also causes the cracks to appear and eventually making the LEDs non-responsive, inoperative and broken. Also, there is no such repairing solution for inoperative LEDs.

Identification Of the Issues

The existence of these common and visible issues thereby demands the manufacturers and engineers to look for issues in circuit board assembly carrying membrane keypads.

It also calls for finding the solution as well. without ever knowing the exact pertaining issues in the system, it consequently becomes more difficult to look for sustainable solutions.

For an instance, if one part of the system doesn’t stick adhesively with other parts, the solution to this problem may also not be so adhesive. The method is famous a classical engineering materials problem.

Solution: Transition from Low Quality to Rigid Circuit Board Assembly

Instead of working around the problem the whole time, the better solution is to simply replace the problematic parts of the keypad designs.

The best solution is to replace the layered keypad membrane board with a silver printed circuit membrane board of about 0.5mm. the solution is sustainable as it carries a strong metal support plate with a highly adhesive acrylic membrane keypad.

Furthermore, the thermal coefficient of this replaced material is way better than that of the polyester acrylic membrane. In addition to these characteristics, the factors such as temperature, vibration, and shocks don’t cause delamination or defects in printed circuit board membrane.

Benefits Of Using Rigid Membrane Switch

Several benefits include:

  • Incorporation of many electronic parts and components with the main keypad assembly unit.
  • We can install surface mount LEDs directly onto the printed circuit boards. It eliminates the LEDs affecting stress and temperature.
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