Analysis of Factors Affecting the Current-Carrying Capacity of Waterproof Connector Metal Terminals: An Experimental Study Based on TE Connectivity’s MCP630 Terminal Current-Temperature Rise and Current-Carrying Capacity Curves

1. How Do We Determine the Performance of Metal Terminals Through Rigorous Testing?

In our experiments, the performance of metal terminals is characterized mainly through the following two graphs:

1.1 Practical Performance: Current-Temperature Rise Curve

This curve serves as the "physical examination report" for electronic components, providing baseline data for thermal stability during the design phase. It reflects the performance of metal terminals under generalized, relatively normal environmental conditions (primarily characterized through thermal responses). It's similar to evaluating a car's stability, fuel efficiency, and failure rate during regular driving conditions. In low-voltage distribution systems, engineers can use this curve to estimate the safety margin during continuous operation of the connector, preventing insulation aging due to uncontrolled temperature rise.

1.2 Performance Limits: Ambient Temperature-Current-Carrying Capacity Curve

This curve reflects the terminal’s maximum performance under the boundary conditions of its application. In other words, it demonstrates the metal terminal’s maximum performance release in high-standard, high-demand usage environments. It's similar to evaluating a car’s extreme performance on a racetrack, like the maximum torque and top speed listed for the Xiaomi SU7 Ultra (incidentally, just like our LiLutong, it aims for both!).

2. How Do the Substrate Material, Coating, and Wire Connection Methods Affect the Current-Carrying Performance of Terminals?

2.1 The Effect of Contact Materials on Current-Carrying Capacity

Through the analysis of the data from Diagram 11 and Diagram 13, we can gain a systematic understanding of how changes in contact materials impact current-carrying capacity.

When the cross-sectional area of the conductor is kept constant, changes in the material’s conductivity are directly reflected in performance. From the current-temperature rise curve, we can observe that when the contact material is changed from high-performance copper alloy to ordinary copper alloy (i.e., when conductivity drops from 64% to 22%), the maximum allowed current-carrying capacity under the USCAR standard 55°C temperature rise requirement only decreases by about 11%.

Moreover, under higher current conditions, the superior thermal stability of contact materials with better conductivity becomes more evident. However, from the temperature rise curve, we can see that if the ambient temperature is relatively high, the difference between the two materials is not as significant.

2.2 The Effect of Coatings on Current-Carrying Capacity

By comparing the data from Diagram 11 and Diagram 12, we observe that coatings seem to have little effect on the current-carrying capacity of metal terminals:

Whether tin-plated (Sn) or gold-plated (Au), the current-temperature rise curves at low and normal temperatures are nearly identical, indicating that the impedance properties of the coating materials have little impact on the terminal’s current-carrying capacity.

This phenomenon suggests that when the resistance properties of the coating materials (silver-plating/tin-plating) are similar, the coating itself has minimal influence on the terminal's current-carrying capacity.

However, the situation is not as simple as it seems. When we break down the experimental data, it becomes clear that we cannot overlook other explanatory features of the data. Notably, when the ambient temperature exceeds 130°C, the current-carrying capacity of tin-plated materials significantly decreases compared to silver-plated materials.

As we all know from basic materials science, silver coatings have superior high-temperature stability and can withstand higher environmental temperatures, whereas tin coatings have lower temperature tolerance, leading to a decrease in their conductivity under high-temperature conditions.

2.3 The Effect of Connection Methods on Current-Carrying Capacity

By comparing the data from Diagram 14 (cold-press connection) and Diagram 17 (welding), it is clear that different connection methods significantly influence the terminal's temperature rise properties, even when the structure, substrate, and coatings are identical.

Why is this the case?

In the field of electrical connector manufacturing, the fundamental differences between cold-press and welding processes determine the physical effects of the two methods. When the metal interface undergoes high-pressure plastic deformation in cold-pressing and melting-crystallization in welding, it results in distinctly different microscopic contact forms: cold-pressed surfaces retain the micro-protrusions formed by the original processing texture, while the welding surface presents a smooth metallurgical interface. This difference in surface morphology, coupled with the characteristic normal load of each process, ultimately creates two different conductive networks at the contact interface — the former forms discrete micro-conductive spots through micro-protrusion tips, while the latter establishes continuous, uniform conductive channels.

Experience shows that the density and size of conductive spots directly determine the "micro-structure" of contact resistance. Cold-pressed interfaces, due to random contact points formed by micro-protrusions, usually have a smaller effective conductive area than the continuous contact surfaces formed by welding. This inherent difference in conductive characteristics, defined by the processing method, is a key consideration for engineers when choosing a manufacturing process for highly reliable connectors. It requires taming the micron-level surface fluctuations while precisely controlling interface load to build an ideal current path at the microscopic level.

In other words, the differences in cold-press and welding during processing result in different surface roughness and loading forces at the contact interface. The size and number of contact points at the interface directly depend on the surface roughness and loading force. As anyone familiar with electrical contact in connectors knows, the size and number of contact points directly determine the contact resistance.

Therefore, cold-press connections may experience higher resistance and greater temperature rise due to insufficient pressure or poor contact. In contrast, welding creates smoother and more secure contact surfaces with lower resistance and smaller temperature rises, thereby improving the terminal's current-carrying capacity.

Conclusions Based on the Theoretical Analysis Above:

• Material Selection Strategy: Optimizing the design of contact materials can enhance both the practical performance and performance limits of the connector when the material's conductivity is significantly improved.
• Coating Optimization Strategy: Although optimizing the coating design may not improve practical performance by much, it can significantly enhance the performance limits.
• Connection Process Strategy: Choosing a superior connection process can notably improve both practical performance and application performance.