Analysis of common problems of silver contacts

Question 1

◆ Adhesion (welding)

This is one of the most common types of failures in electronic connectors. Below are some possible causes of failure.

● Stain or corrosion on the contact surface will increase the contact resistance, so it is easier to stick when the contact temperature is raised.

● Loose riveting, a poor solder joint or brazing joint can also lead to increased resistance, resulting in adhesion.

● The unreasonable contact combination makes the effective contact area too small, resulting in increased resistance and adhesion.

● Too small contact force or separation force caused by unreasonable mechanical motion design may also cause adhesion.

● Higher currents may create more localized sticking than usual

For new product applications, in addition to the above, there are:

● Ensure the reasonable size of the contacts and the correct selection of materials.

● At the same time, it should be noted that materials with high thermal conductivity should be selected as much as possible, so as to keep the contacts from overheating. This factor should not be ignored, and it is usually the key to success and failure.


Question #2

◆ High contact corrosion

If the contacts are corroding too fast, check for all the factors we have mentioned for sticking defects, since these same factors can cause increased corrosion rates, even those conditions are not met enough to cause corrosion, plus:

● Check for contact chatter, if the switch is humming when closing, corrosion may be greatly increased.

● For AC circuits, connections should not be disconnected too quickly, but fast enough to reduce sparking and slow enough to reduce arc length. When the voltage is close to zero, and the disconnection distance is large enough, there will be no sparks. For DC circuits, a fast enough opening speed helps reduce sparking, and whether it is AC or DC circuits, fast closing and reduced chatter are beneficial.

● As with any equipment, reducing arc duration or intensity will reduce corrosion.

● Lower contact force can reduce mechanical corrosion within a reasonable limit. However, if the contact force is too low, the increase in galvanic corrosion will outweigh the reduction in mechanical corrosion.


Question #3

◆ Contact material transfer

Material transfer is generally caused by the polarity of the direct current, and in the absence of an arc, the phenomenon of metal bridge transfer causes material to transfer from the anode contact to the cathode contact.

● If the contact is under arcing conditions, in addition to the metal bridge transfer, another phenomenon will also occur. Under the action of the arc, the material is sprayed from the cathode contact to the anode contact. We call it "arc transfer". The strength of transfer and arc transfer will ultimately determine the direction of material transfer.

● In DC circuits, the choice of contact material is very important to reduce material transfer defects. High melting point and boiling point, good soldering resistance, good electrical and thermal conductivity, and high hardness help reduce material transfer.


Question #4

◆ High contact resistance

Often external stains or corrosion on the contacts can result in high contact resistance resulting in overheating, welding, high corrosion rates or failure to complete the circuit at all.

● Selecting contact materials for different use environments helps reduce corrosion.

● A sealed work environment will eliminate or reduce stains.

● Before installation, the contacts should be cleaned as much as possible.

● In the structural design, the sliding should be minimized, which can effectively reduce the appearance of stains.