In order to make the pcb connector better protect the substrate, we generally plate a protective film on the surface of the contact terminal. This coating is either tinned or gold plated. The quality of the coating determines the service life of the connector to some extent. Today we take a look at the reasons for the differences in the gold-plated surface:
1. Influence of impurities in gold-plated raw materials
When the impurities added into the chemical materials added to the plating solution exceed the tolerance of the gold plating solution, it will quickly affect the color and brightness of the gold layer. If it is under the influence of organic impurities, the phenomenon of darkening and flowering of the gold-plated layer will appear, and the Haoer slot test checks that the darkening and flowering positions are not fixed. If it is the interference of metal impurities, the effective range of current density will be narrowed, then the result of Haoer slot test will be that the current density of the test piece is not bright or the high end is not bright and the low end is not plated. It is reflected that the plating layer is red or even black, and the color change in the hole is more obvious.
2. Gold plating current density is too large
Due to incorrect calculation of the total area of the parts of the plating bath, the value is greater than the actual surface area, which makes the gold plating current too large, or the amplitude is too small when using vibrating gold plating, so that all or part of the gold plating layer in the groove is crystallized rough, and the appearance of the gold-plated layer also appeared red.
3. Gold plating solution aging
If the gold plating connector solution is used for too long, the excessive accumulation of impurities in the plating solution will inevitably cause abnormal color of the gold layer.
4. The alloy content changes in the hard gold coating
In order to improve the hardness and wear resistance of the connector, the gold plating of the connector generally adopts the hard gold plating process. Among them, gold-cobalt alloy and gold-nickel alloy are mostly used. When the content of cobalt and nickel in the plating solution changes, the color of the gold plating layer will change. If the cobalt content in the plating solution is too high, the color of the gold layer will be reddish; if the nickel content in the plating solution is too high, the color of the metal will become lighter; if the change in the plating solution is too large, and the different parts of the same supporting product are not in the same tank When gold-plating, this will cause the same color of the gold layer of the same batch of products provided to the user.
5. No gold plating in the hole
After the gold plating process of the pin or socket of the connector is completed, when the thickness of the outer surface of the plated part reaches or exceeds the specified thickness value, the plating layer of the inner hole of the welding wire hole or the socket is very thin or even no gold layer.
6. When gold plating, the plated parts are inserted into each other
In order to ensure that the socket of the connector has a certain flexibility when plugging and unplugging, most types of sockets are designed with a split groove at the insertion port during product design. During the electroplating process, the plated parts are constantly turned, and some of the jacks are inserted into each other at the opening, which makes it difficult to electroplating the holes due to the mutual shielding of the power lines at the insertion parts.For example,the pin headers assembled in the below machined female headers are very prone to appear when electroplating.
7. When the gold plated parts are connected end to end
In some types of connectors, the pin diameter of the pin is slightly smaller than the hole diameter of the wire hole during the design. During the electroplating process, some pins will form a head-to-tail connection, resulting in no gold plating in the hole . (See illustration) The above two phenomena are more likely to occur during vibration gold plating.
8. The concentration of the blind hole is greater than the deep plating ability of the electroplating process
Because there is still a distance between the bottom of the slot of the jack and the bottom of the hole, this distance objectively forms a blind hole. There is also such a blind hole in the wire hole of the pin and the jack, which provides a guiding role when the wire is welded. When the pore diameter of these holes is small (often less than 1 mm or even less than 0.5 mm) and the concentration of the blind hole exceeds the pore size, the plating solution is difficult to flow into the hole, and the plating solution flowing into the hole is difficult to flow out, so the hole The quality of the gold layer is difficult to guarantee.
9. The area of the gold-plated anode is too small
When the volume of the connector is small, the total surface area of the single-slot plated parts is relatively large, so that if there are more single-slot plated parts when plating small pinhole parts. The original anode area is not enough. Especially when the platinum titanium mesh is used for too long, and the platinum loss is too much, the effective area of the anode will be reduced, which will affect the deep plating ability of the gold plating, and the plating hole will not be plated.
10. Poor adhesion of plating
When checking the adhesion of the plating layer of the connector after plating, sometimes the front part of the pin end of some pins is bent or the welding wire hole of the pin hole piece is flattened when the flattening of the welding wire hole, sometimes at high temperature (2000 hours) The detection test found that the gold layer has a very small bubbling phenomenon.
11. Incomplete treatment before plating
For small pinhole parts, if the trichloroethylene ultrasonic degreasing cannot be used immediately after the machining process is completed, it is difficult to remove the dried oil in the hole after the next conventional pre-plating treatment, so the plating in the hole The binding force will be greatly reduced.
12. Incomplete activation of substrate before electroplating
Various types of copper alloys are widely used in connector base materials. Trace metals such as iron, lead, tin, beryllium and other trace metals in these copper alloys are difficult to activate in general activation liquids. If they are not activated by corresponding acids, electroplating is performed. At this time, the oxides of these metals are difficult to combine with the coating, which causes the high temperature blistering of the coating.
13. Low plating solution concentration
When using nickel sulfamate plating solution for nickel plating, when the nickel content is lower than the process range, the quality of the plating layer in the hole of small pinhole parts is affected. If the gold content of the pre-plating solution is too low, then the gold may not be plated in the hole during gold plating. When the plated part enters the thickened gold plating solution, the nickel layer in the hole of the metal part of the hole is dull As a result, the binding force of the gold layer in the hole is naturally poor.
14. No reduction in current density when plating slender pins
When plating slender pins, if the current density is used for electroplating, the coating on the tip of the needle will be much thicker than that on the needle shaft. Observing the tip of the needle under a magnifying glass sometimes takes the shape of a match head. The plating on the head and neck, that is, the gold plating on the top of the front end of the pin, is not qualified when the bonding force is checked. This phenomenon is likely to occur during vibration gold plating.
15. Vibration gold-plated vibration frequency adjustment is incorrect
When using vibration electroplating connectors, if the vibration frequency is not adjusted correctly during nickel plating, the plated parts will jump too fast, and it is easy to open into double nickel, which has a great influence on the bonding force of the plating layer.