1. Can the metal dome of a button be directly soldered to the circuit board? What are the pros and cons?
2. Although modern smartphones rarely utilize physical keys, some products still feature a few tactile buttons. PCB products continue to incorporate physical keys. The “metal dome” offers the best tactile feedback and the longest lifespan, but a significant drawback is that it occupies excessive space on the circuit board. As a result, PCB R&D teams began to explore innovative solutions. On a whim, they soldered the “metal dome” directly onto the circuit board to function as a button, which did increase available space for electronic components, but also led to some unforeseen issues.
3. Generally, the PCB space beneath the keys (keypad) is not typically utilized for electronic components. Currently, most “metal domes” on the market consist of a single piece of adhesive. They are applied to physical buttons or circuit boards to save labor time and ensure the precision and stability of the “metal dome.” Shenzhen Honglijie believes that many forward-thinking R&D engineers have contemplated the idea of soldering “metal domes” directly to the circuit board to maximize usable space. However, most R&D professionals, even with some experience, hesitate to encroach on the area near the button, let alone solder components directly onto the PCB.
Because there is currently no off-the-shelf “metal reed” that can be directly soldered to circuit boards, our R&D team decided to design a “metal reed” with a pair of symmetrical wings that can be flat-mounted on the surface of the circuit board. These wings are then soldered onto the board using solder paste. However, after the product was tested for button longevity, we found that the button failed to respond after just over 100K presses. Upon disassembly, we discovered that a tin crack had formed on the wings of the “metal reed,” causing it to lose its original position on the circuit board.
Initially, R&D approached Shenzhen Honglijie as usual to address the tin cracking issue. We inquired whether the factory could enhance the soldering process. As a result, we manually increased the amount of solder, covering the entire wings with tin. However, this hand-soldering method is not feasible for mass production. Fortunately, during subsequent life tests, the product survived just over 300K presses before the “metal reed” wings actually broke, indicating that additional tin was unnecessary.
**Advantages of Directly Soldering the “Metal Reed” to the Circuit Board:**
– It saves space on the circuit board, allowing for the arrangement of other components around the metal reed.
– Cost savings can be realized, as the reduced space on the PCB can lower overall manufacturing costs.
**Disadvantages of Directly Soldering the “Metal Reed” to the Circuit Board:**
These drawbacks can be significant. Beyond the aforementioned issue of wing fracture, various engineering and quality challenges remain to be addressed.
– **Floating “Metal Reed”:**
Due to the use of solder paste, some solder paste may accumulate beneath the metal reeds. Depending on the amount applied, this can lead to the reeds lifting off the circuit board’s surface. High-floating reeds necessitate greater force or longer presses to trigger the button function, leading to inconsistent actuation among the reeds.
– **Tilted “Metal Reed”:**
When the reeds float excessively, they may tilt unevenly on the circuit board. A larger gap increases the risk of dust or foreign particles getting lodged underneath, which can interfere with the button’s trigger mechanism and result in a failure to respond when pressed.
Minor contamination issues can sometimes be mitigated by employing “metal reeds” with a dimple design, but serious issues remain unresolved.
– **Solder Climbing the Inner Wall of the “Metal Reed”:**
This is a particularly troublesome issue that is best addressed through design. When the solder paste melts, it flows toward areas with lower surface energy, including the “metal reed.” Because the reed is heated during soldering, there is a significant risk of solder creeping along its inner wall. This can impair the tactile feedback when pressing the button. If solder accumulates in the reed’s web area, it can hinder actuation, increasing the Peak Force (F1) required to press the button, adversely affecting the button’s click ratio and tactile sensation. Variations in the height and thickness of the solder on the inner wall can lead to inconsistent pressing experiences.
**Postscript:**
Why does the welding of wings on the “metal reed” lead to breakage? What are your thoughts?
Certainly, the R&D team’s ethos is to persevere through setbacks, and this story continues with potential breakthroughs on the horizon. As they say, failure is the mother of success! It takes courage to push beyond constraints, but the costs remain uncertain.
To enhance circuit board utilization beneath the button, one potential solution is to elevate the button with mechanical components and replace the original contact point with a flexible board, thus preserving the original circuit board’s functionality.
2. Although modern smartphones rarely utilize physical keys, some products still feature a few tactile buttons. PCB products continue to incorporate physical keys. The “metal dome” offers the best tactile feedback and the longest lifespan, but a significant drawback is that it occupies excessive space on the circuit board. As a result, PCB R&D teams began to explore innovative solutions. On a whim, they soldered the “metal dome” directly onto the circuit board to function as a button, which did increase available space for electronic components, but also led to some unforeseen issues.
3. Generally, the PCB space beneath the keys (keypad) is not typically utilized for electronic components. Currently, most “metal domes” on the market consist of a single piece of adhesive. They are applied to physical buttons or circuit boards to save labor time and ensure the precision and stability of the “metal dome.” Shenzhen Honglijie believes that many forward-thinking R&D engineers have contemplated the idea of soldering “metal domes” directly to the circuit board to maximize usable space. However, most R&D professionals, even with some experience, hesitate to encroach on the area near the button, let alone solder components directly onto the PCB.
Because there is currently no off-the-shelf “metal reed” that can be directly soldered to circuit boards, our R&D team decided to design a “metal reed” with a pair of symmetrical wings that can be flat-mounted on the surface of the circuit board. These wings are then soldered onto the board using solder paste. However, after the product was tested for button longevity, we found that the button failed to respond after just over 100K presses. Upon disassembly, we discovered that a tin crack had formed on the wings of the “metal reed,” causing it to lose its original position on the circuit board.
Initially, R&D approached Shenzhen Honglijie as usual to address the tin cracking issue. We inquired whether the factory could enhance the soldering process. As a result, we manually increased the amount of solder, covering the entire wings with tin. However, this hand-soldering method is not feasible for mass production. Fortunately, during subsequent life tests, the product survived just over 300K presses before the “metal reed” wings actually broke, indicating that additional tin was unnecessary.
**Advantages of Directly Soldering the “Metal Reed” to the Circuit Board:**
– It saves space on the circuit board, allowing for the arrangement of other components around the metal reed.
– Cost savings can be realized, as the reduced space on the PCB can lower overall manufacturing costs.
**Disadvantages of Directly Soldering the “Metal Reed” to the Circuit Board:**
These drawbacks can be significant. Beyond the aforementioned issue of wing fracture, various engineering and quality challenges remain to be addressed.
– **Floating “Metal Reed”:**
Due to the use of solder paste, some solder paste may accumulate beneath the metal reeds. Depending on the amount applied, this can lead to the reeds lifting off the circuit board’s surface. High-floating reeds necessitate greater force or longer presses to trigger the button function, leading to inconsistent actuation among the reeds.
– **Tilted “Metal Reed”:**
When the reeds float excessively, they may tilt unevenly on the circuit board. A larger gap increases the risk of dust or foreign particles getting lodged underneath, which can interfere with the button’s trigger mechanism and result in a failure to respond when pressed.
Minor contamination issues can sometimes be mitigated by employing “metal reeds” with a dimple design, but serious issues remain unresolved.
– **Solder Climbing the Inner Wall of the “Metal Reed”:**
This is a particularly troublesome issue that is best addressed through design. When the solder paste melts, it flows toward areas with lower surface energy, including the “metal reed.” Because the reed is heated during soldering, there is a significant risk of solder creeping along its inner wall. This can impair the tactile feedback when pressing the button. If solder accumulates in the reed’s web area, it can hinder actuation, increasing the Peak Force (F1) required to press the button, adversely affecting the button’s click ratio and tactile sensation. Variations in the height and thickness of the solder on the inner wall can lead to inconsistent pressing experiences.
**Postscript:**
Why does the welding of wings on the “metal reed” lead to breakage? What are your thoughts?
Certainly, the R&D team’s ethos is to persevere through setbacks, and this story continues with potential breakthroughs on the horizon. As they say, failure is the mother of success! It takes courage to push beyond constraints, but the costs remain uncertain.
To enhance circuit board utilization beneath the button, one potential solution is to elevate the button with mechanical components and replace the original contact point with a flexible board, thus preserving the original circuit board’s functionality.
