The Importance of Dimples in Metal Dome Keypads

Keypad contact pad with fiber contaminationforeign dust contaminate inside metal dome and make contact fail.

Recently, our company introduced metal dome technology as a contact solution for rubber keypads, a trend also seen in many cell phone keypad designs. The advantages of using metal domes include a better key press experience, extended lifespan, and improved reliability. According to data, metal dome keypads can endure 2,000,000 finger presses compared to the 300,000 presses of poly-dome keypads.

Initially, we removed the dimple from the metal dome to increase the key press lifespan. This decision was made to prevent potential damage to the contact pad on the PCB and avoid the formation of verdigris from the copper layer on the PCB base. Verdigris can lead to disconnection between the metal dome and the PCB contact pad, resulting in keypad malfunctions.

After several product trial runs, we discovered that removing the dimple not only failed to improve key press lifespan but also led to issues with keypad insensitivity. While the key press feeling was good, the keys did not function properly with slight presses. More force was required to activate the key function, and in some cases, keypad insensitivity occurred after a period of use.

Upon investigating the insensitive keypad issue, we identified that tiny dust or fibers under the metal dome or on the PCB contact area caused this defect. When lightly pressing a key, these foreign particles hindered the metal dome’s contact with the PCB during gentle presses. While applying more force to the keyboard could break through these obstacles and establish circuit connectivity, it still posed significant usability challenges.

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