Structure and lifespan design of silicone buttons

The remote control works fine when pressed for ten years, while some products malfunction after six months - silicone buttons look simple, but the lifespan difference is very large. The buttons are a long-standing application of silicone, and are still widely used from remote controls to industrial control equipment panels. This article discusses the structural principles of silicone buttons and the factors that determine their lifespan.

The working principle of silicone buttons

A typical silicone button (a pure silicone structure outside of the pot piece structure) utilizes the elastic deformation of the thin-walled part of the silicone - the top of the button is subjected to force, pressed down to the bottom contact point to contact the PCB, and released by the rebound of the silicone itself to reset. The part that undergoes back and forth deformation is called the "elastic wall", which is usually a slanted wall surrounding the button pillar.

The elastic wall is the heart of the button. Its wall thickness, angle, and height determine three key tactile parameters:

Operating Force - how much force is needed to press down, usually 80-300gf, and remote control usually 100-150gf; Rebound Force - the force that bounces back when released, affecting whether the feel is "brittle"; Travel - the distance pressed, usually 0.5-2mm, affects whether the tactile sensation is clear.

The ratio of rebound force to pressing force is generally greater than 40%. Below this value, the hand feels stuffy and feels like pressing on cotton.

What determines lifespan

The standard action for key life testing is to repeatedly press at the rated pressing force (such as 100000, 500000, 1 million times), and measure the attenuation of pressing force and rebound force. At the end of its lifespan, it manifests as weak rebound (decreased hand feel) or fatigue fracture of the elastic wall (functional failure).

Factors affecting lifespan:

Elastic wall design - uniform wall thickness, smooth transition, and long lifespan of the elastic wall; The area with sudden wall thickness changes or sharp corners is the starting point of fatigue cracks. A well-designed elastic wall with a lifespan of one million cycles is not difficult; A design error of 300000 times can lead to fatigue.

Selection of rubber material - When using rubber material for buttons, both rebound and fatigue resistance should be taken into account. Cheap rubber materials with low tear strength can be used for elastic walls, and their lifespan can be reduced by half. High life buttons (over 1 million times) are generally specified with anti fatigue formula rubber.

Hardness - Shore A 50-70 is a common range. Too soft with insufficient rebound, too hard with a stiff hand feel and high wall stress.

Sulfurization quality - buttons with insufficient vulcanization, insufficient cross-linking density in the elastic wall area, and permanent deformation after a few bounces. This is also one of the reasons why the buttons need to be 100% post vulcanized.

Quantification of tactile sensation

Texture is not mystical. A professional button factory uses a tactile tester to draw a "force stroke curve", where the slope, peak value, and falling edge shape of the curve fully describe the tactile sensation of a button. The customer said 'to be more crisp' and 'to have a paragraph feel', which translates to curve parameters as executable design inputs. That's also why buttons made by different factories have different tactile sensations on the same drawing - the drawing only defines the size, and the tactile sensation is still hidden in the rubber material and vulcanization process.

The lifespan of character printing

The lifespan of buttons is not only the lifespan of pressing, but also includes the wear resistance of characters. The molded characters will not fall off; Screen printed characters must undergo RCA abrasion resistance or alcohol friction testing; High demand laser engraving. The characters are worn out and the buttons play well, but users still feel that they are "broken".

Key points of procurement acceptance

To confirm the hand feel, it is necessary to make a sample and it is best for both parties to seal the standard hand feel sample. Write the lifespan into the specifications: the rebound force will decay by no more than 20% after X million presses. The appearance and size of the bullet wall are key inspection items, and bubbles, material shortages, and uneven wall thickness are all concentrated on the bullet wall. For products with high lifespan requirements, ask suppliers to provide lifespan test data of the same structure, don't bet. The button is a small product, but it is a component that "people come into contact with hundreds of times a day", and poor feel and malfunction are directly perceived by users as experience problems. A factory that excels in this category has accumulated experience in elastic wall design, rubber materials, vulcanization, and printing, and not just any silicone factory can do it well.