Press Fin Or Reflow Soldering

When selecting a PCheat sink, one encounters a variety of dazzling terms. What exactly are press fin & reflow soldering? Mirror copper bottom? Heat pipe direct contact? Hot plate? Which is better? What exactly is a Fin? This column aims to provide answers to these questions, both theoretically and practically.

What are fins for?

The term "Fin," short for "fin," refers to the thin sheets on aheat sink, typically made of copper or aluminum. Many newcomers to heat sinks assume that heat pipes directly handle heat dissipation, but this is not the case. Heat pipes merely act as conduits, transferring heat from the base (chip) to the fins. The fins themselves play the critical role of exchanging heat with the air, utilizing their surface area to facilitate heat dissipation.

Even with robust heat pipes, inadequate fin area can hinder optimal heat dissipation efficiency. It's common to see large aluminum extrusion heat sinks covering motherboard south bridges and power supplies without heat pipe designs, for this reason.

Today, heat pipes receive more attention while fins are often overlooked. However, hidden within these small fins are numerous craftsmanship secrets.

What is Press Fin and Reflow Soldering?

Press fin & reflow welding refer to methods of connecting fins to heat pipes within aheat sink. In aheat sink, fins must absorb heat from heat pipes and dissipate it into the air with the aid of airflow. Therefore, the mode of contact between heat pipes and fins is crucial in determining heat dissipation efficiency.

Reflow Soldering

Reflow soldering involves firmly soldering fins onto heat pipes. Solder is applied to the heat pipe, the fins are then threaded onto the pipe, and finally, theheat sink undergoes heating in a reflow soldering machine. During heating, solder paste fills the gap between the heat pipe and the fin due to gravity and capillary action, resulting in a secure connection.

Reflow soldering requires small openings near the heat pipe for solder filling and reflow solder paste. These openings are typically visible onheat sinks using reflow soldering.

However, some savvy businessmen may simulate reflow soldering by creating similar openings onheat sinks that do not actually use reflow soldering.

Reflow soldering ensures a firm and tight connection between fins and heat pipes but comes with higher costs and a longer manufacturing process.

Press Fin

"Press fin" involves connecting materials at lower temperatures. This method relies on external forces and material elasticity to tightly embed fins into the heat pipe wall, facilitating heat conduction. It's akin to a "big force miracle," where a large part is forced into a smaller hole through interference fit.

Press fin does not require solder or high temperatures, thus reducing material costs. However, it is prone to wear and tear, requires high tolerance levels for quality, and once compromised, restarting the process is challenging, significantly affecting yield. Over time, differences in copper and aluminum thermal expansion coefficients can create gaps, loosening initially tight fins and reducing heat dissipation efficiency.

Which performs better: Reflow soldering or Press Fin?

It's essential to clarify that reflow soldering does not necessarily equate to superior performance. Due to the challenges in welding different materials like copper and aluminum, reflow soldering requires a transition layer—often nickel—to assist in the process. However, nickel itself has poor thermal conductivity, and solder (tin) also contributes to thermal resistance.

In contrast, high-quality press fin can achieve significantly lower thermal resistance than reflow soldering products, potentially offering stronger performance. However, due to stringent tolerance requirements, fewer manufacturers produce high-quality press fin products. Therefore, reflow soldering remains popular among high-endheat sink manufacturers despite its higher costs.

Conclusion

Reflow welding offers stronger durability but lower theoretical performance and higher costs. In contrast, press fin provides lower material costs and potentially superior theoretical performance but demands high tolerance levels and faces challenges with durability over time.

The choice between these methods is not absolute and should be guided by specific work requirements and demands.