Surface mount IC substrate packaging relies on printed circuit boards (PCBs) for heat dissipation. Generally, PCBs serve as the primary cooling method for high-power semiconductor devices. Effective PCB heat dissipation design is crucial as it significantly influences system performance and mitigates the risk of thermal incidents. Thoughtful management of PCB layout, structure, and device mounting enhances heat dissipation in medium and high-power applications.
To optimize heat dissipation, the top and bottom layers of the PCB are critical. Using wider traces and routing them away from high-power devices creates efficient heat dissipation paths. Incorporating a dedicated heat spreader is an excellent strategy for PCB thermal management. Typically positioned on the top or backside of the PCB, these spreaders establish thermal links with devices through direct copper contact or thermal vias.
In single-sided packaging (where leads are only on one side), the heat spreader can be placed atop the PCB, often adopting a “dog bone” shape (narrow at the center where the device sits and broader at the ends where copper connections extend). For quad-sided packaging (leads on all four sides), the heat spreader must be situated behind or integrated within the PCB. Larger PCB systems may also integrate cooling solutions. By connecting the heat spreader to the ground plane with screws, these fasteners enhance heat dissipation, albeit their effectiveness should balance with cost considerations.
Metal reinforcement plates on the PCB, once connected to the heat spreader, increase cooling surface area. In applications where PCBs are housed, using controlled welding materials offers superior thermal performance compared to air-cooled enclosures. While fans and heat sinks remain popular cooling solutions, they often require design modifications for optimal effectiveness due to space constraints.
Preparing BGA IC substrate boards involves applying solder paste to the solder leg side, evenly distributing it with a hot air gun. Some mobile phone circuit boards pre-print positioning frames for BGA IC substrate boards, simplifying alignment during soldering. However, boards lacking such frames require alternative positioning methods.
This revision aims to enhance clarity and readability while maintaining the original content’s technical focus on PCB heat dissipation strategies and assembly processes.
1) Line drawing positioning method: Before removing the BGA-IC substrate board, use a pen or needle to draw lines around it, marking the direction for re-welding. This method offers accuracy and convenience; however, pen-drawn lines are easily erased, and care is needed with needle-drawn lines to avoid damaging the circuit board.
2) Sticker positioning method: Prior to removing the BGA-IC substrate board, affix label paper along its four sides on the circuit board, aligning precisely with the edges using tweezers for secure attachment. This creates a positioning frame post-removal, simplifying reinstallation. Quality label paper with strong adhesion is essential to prevent detachment during reflow soldering. If the label paper feels too thin, layering multiple sheets can create a thicker base. Trim the edges neatly with scissors for better fit when replacing the IC substrate board. Some technicians use materials like plaster or metal clamps for marking and positioning, but I find the sticker method more convenient and less likely to cause damage or contamination to the circuit and other components.
3) Visual inspection method: When installing the BGA-IC substrate board, first position the IC carrier plate upright to view both the pins on the IC substrate board and the circuit board simultaneously. Compare the alignment horizontally and vertically with reference to the circuit board lines, ensuring precise orientation before installation.
4) Touch method: After removing the BGA-IC substrate board, apply sufficient solder paste on the circuit board and smooth each solder leg with an electric soldering iron to achieve rounded joints. Avoid using desoldering wick to flatten joints, as this would hinder the subsequent touch method. Gently maneuver the BGA-IC substrate board with solder balls across the circuit board, noting any resistance or movement indicating alignment. If a circuit board pad remains visible around the IC substrate board’s edges, it signals misalignment necessitating repositioning. Once aligned, solder the BGA-IC substrate board carefully using a hot air rework station, adjusting airflow and temperature for even heating until solder fusion is evident by overflow. During heating, avoid pressing the BGA-IC substrate board forcibly to ensure proper alignment facilitated by surface tension of the solder joints.
