What is Contact Resistance

By Bester PCBA

Last Updated: 2023-08-07

What is Contact Resistance

Contact resistance is the electrical resistance that occurs when two conductive materials or components come into contact with each other. It is the resistance encountered at the point of contact between the conducting surfaces. Contact resistance is a critical factor to consider in the design and manufacturing of PCBs as it directly impacts the efficiency and reliability of electrical connections. High contact resistance can lead to voltage drops, power losses, and increased heat generation, which can negatively affect the functionality and efficiency of the circuit.

Several factors influence contact resistance, including surface conditions, cleanliness, and the materials used for the contact surfaces. Imperfections such as surface roughness, contaminants, oxides, or damaged plating can increase the resistance at the contact point.

To minimize contact resistance, it is important to use materials with low resistivity for the contact surfaces, such as gold or silver, which provide good electrical contact. Proper cleaning and surface treatment techniques can also be employed to remove contaminants and oxides, ensuring a low-resistance connection.

Contact resistance is typically measured using an Ohmmeter or Ductor tester, which accurately measures the resistance at the micro- or milli-ohm level. Regular testing is essential to ensure proper electrical connections and detect any issues such as loose connections, eroded contact surfaces, or contaminated contacts.

Frequently Asked Questions

What Is the Contact Resistance of a Circuit

Contact resistance refers to the resistance that occurs when contacts are touching each other in a closed circuit, caused by surface conditions and other factors. This resistance can be observed between contacts of breakers. The contact resistance is typically measured in micro-ohms (μΩ) and is estimated to be around 20 μΩ.

What Is the Difference Between Resistance and Contact Resistance

The distinction between resistance and contact resistance lies in the measurement methods used. When using the two-lead and four-lead methods, the resistance obtained is a reliable measurement of contact resistance, as long as the resistance of the leads is significantly smaller. To determine the specific contact resistance, it is necessary to multiply the obtained resistance by the contact area. Additionally, it is important to note that contact resistance may vary depending on the temperature.

How Do You Reduce Contact Resistance

Using multiple electrodes at each cable take-out and connecting them together ‘in parallel’ with cable jumpers can effectively reduce contact resistance. By adding a second electrode, the contact resistance can be reduced to approximately 60% of its initial value. Furthermore, adding another electrode will further decrease it to 40% of the initial value. Subsequently, adding additional electrodes after this will continue to decrease the contact resistance.

How Can I Improve My Contact Resistance

Contact resistance can be decreased by increasing the pressure, current, or voltage, or by applying an alternating current (AC) on top of a direct current (DC).

What Affects Contact Resistance

High junction loads and high temperatures can cause low contact resistances, while light junction loads and low temperatures can result in high contact resistances. Additionally, the surface finish, including the roughness and flatness of the contacting surfaces, can have a significant impact on the magnitude of the contact resistance.

What Are the Effects of High Contact Resistance

Higher contact resistance has several effects. It leads to increased power consumption and temperature rise. Additionally, it results in undesirable interconnectivity between electrode materials, which negatively impacts the electrical lifespan and reliability of switching devices.