Unique Requirements of HotBar in PCB Manufacturing
PCB companies have long been grappling with the specific demands of HotBar technology. The need for a three-layer FPC to facilitate HotBar, with pads limited to one side, poses a challenge. This setup prevents direct contact between the hot press head and the solder pads on the FPC and PCB, necessitating thermal energy to traverse the FPC layers for effective heat transfer and solder melting.
Challenges and Solutions
While the HotBar process is complex, it is not insurmountable. The main concern lies in the potential for FPC burning due to excessive heat exposure, leading to reliability issues during quality assessments.
Alternative Methods
- Utilizing low-temperature solder paste with the HotBar machine for FPC welding is one approach. However, this solder paste may exhibit lower reliability, making it susceptible to brittleness and pulling forces. Direct printing on the PCB side is not recommended unless for specific components.
- Soldering the FPC directly using SMT through a furnace is another method. Manual adjustments and a custom fixture may be required for this process.
ACF Consideration
While some suggest using Anisotropic Conductive Film (ACF) as an alternative to HotBar, its bonding strength may be insufficient for certain applications. ACF exhibits low reliability over time, especially in high-temperature and humid environments, necessitating additional protective measures for enhanced peel strength.
Low-Temperature Solder Paste
Indium 5.7LT 58Bi/42Sn low-temperature solder paste, with a melting point of 138°C, offers a promising solution. After HotBar pressing, the peel force tested at 1.5 Kgf, indicating room for improvement. LED components utilizing low-temperature solder paste have shown a thrust of 4.0 Kgf, highlighting the potential for enhanced performance.
In conclusion, addressing the challenges posed by HotBar technology in PCB manufacturing requires innovative solutions and careful consideration of materials and processes to ensure optimal results.
