1).PCB surface treatment process includes: oxidation resistance, tin spraying, lead-free tin spraying, sink gold, sink tin, sink silver, hard gold plating, full plate gold plating, goldfinger, nickel palladium gold OSP, etc. The main requirements are: low cost, good weldability, harsh storage conditions, short time, environmental protection technology, good welding, flat. Tin spraying: tin spraying board is usually multi-layer (4-46 layers) high-precision PCB model, which has been used by many large communication, computer, medical equipment and aerospace enterprises and research units in China.
2).The connecting finger is the connection between the memory slot and the memory strip on which all the signals are sent. Goldfinger is composed of many golden conductive contact pieces, because its surface is gilded and conductive contact pieces are arranged like fingers, so called "goldfinger", goldfinger plate needs to be gilded or heavy gold. Goldfinger actually adds a layer of gold to the copper sheet by a special process, because gold is highly antioxidant and highly conductive. Because the price of gold is expensive, however, the current tin plating is used to replace the more memory, tin material from the last century 90 s began to spread, the motherboard, memory, and video devices such as "golden finger" is almost always used tin material, only some high-performance server/workstation accessories will contact point to continue the practice of using gold plated, the price expensive.
2. Difference between gold-plated and gold-plated processes:
1). The method of sinking gold is chemical deposition. A layer of coating is generated by chemical REDOX reaction.
Gold plating USES the principle of electrolysis, also known as electroplating. Other metal surface treatment is also mostly used in the form of electroplating.
In the actual product application, 90% of the gold plate is sunken gold plate, because the poor weldability of the gold-plated plate is his fatal defect, is also the direct reason that leads many companies to abandon the gold-plated process!
2). Deposit nickel gold coating with stable color, good brightness, smooth coating and good solderability on the surface of printed lines by gold sinking process. It can be basically divided into four stages: pretreatment (oil removal, micro erosion, activation, post-leaching), nickel precipitation, gold precipitation, post-treatment (waste gold washing, DI washing, drying). The thickness of gold deposit is between 0.025-0.1um.
3). Gold is applied to the circuit board surface treatment, because of the strong conductivity of gold, good oxidation resistance, long life, general application such as button plate, goldfinger plate, etc., and the most fundamental difference between gold-plated plate and sink gold plate is that gold-plated is hard gold (wear resistance), sink gold is soft gold (not wear resistance).
(1) the crystal structure formed by gold plating is not the same as that formed by gold plating. The thickness of gold plating is much thicker than that of gold plating. Gold plating will be golden in color and more yellow than gold plating (this is one of the ways to distinguish between gold plating and gold plating).
(2) different from the crystal structure formed by gold-plating, the gold-plating phase is easier to weld and will not cause poor welding. The stress of sunken gold plate is more easily controlled, which is more conducive to the processing of bunding for products with bunding. At the same time, it is also because the heavy gold is softer than the gilt, so the heavy gold plate does not wear goldfinger (the defect of the heavy gold plate).
(3) there is only nickel gold on the welding pad of the sunken gold plate, and the signal transmission in the skin effect is in the copper layer, which will not affect the signal.
(4) compared with gold plating, the crystal structure is denser, and it is not easy to produce oxidation.
(5) as the machining precision of circuit board is required to be higher and higher, the line width and spacing have reached less than 0.1mm. Gold plating is easy to produce a short circuit of gold wire. There is only nickel gold on the plate, so it is not easy to produce a short circuit of gold wire.
(6) there is only nickel gold on the plate, so the combination of resistance welding and copper layer on the line is more solid. The engineering will not affect the spacing when making compensation.
(7) for the higher requirements of the board, the flatness requirements are good, generally use heavy gold, heavy gold generally will not appear after the assembly of the black mat phenomenon. The flatness and service life of countersunk gold plate is better than that of gilded plate.
3.How to control gold-plated PCB material:
1).Potion stability is the decisive factor affecting the reaction rate of gold plating. The concentration of gold ions, as the main consuming component of the gold-plating reaction, also fluctuates with the production consumption, and the fluctuation of the gold salt concentration in turn leads to the fluctuation of the gold-plating reaction rate. Therefore, in order to ensure a stable rate of gold-plating reaction, it is necessary to keep the concentration of gold salt in the gold bath at a more stable level. On the premise of potion stability, the setting and adjustment of gold-plated parameters will be more accurate, the thickness of the gold-plated layer will be more stable control. In order to maintain the stability of the gold salt concentration in the gold tank, the following two points should be noted:
(1) maintain the accuracy and completeness of production records;
(2) maintain the timeliness of gold salt supplementation and follow the principle of "several times with small amount".
2). Optimize the uniformity of gold plating:
If the uniformity of gold plating is low, it will seriously affect the control of the thickness of gold plating in the production process. In the process of production, in order to meet the customer's requirements for the minimum thickness of the gold-plated layer, the gold-plated layer is often made thicker, resulting in a serious waste of gold salt. In order to optimize the uniformity of thick gold plating groove, it can be improved by changing the setting mode and position of titanium anode mesh in the groove, and the best solution can be found through technical test. At the same time, in the process of gold plating, for the relatively small production plate, can be equipped with anode baffle for production, can also significantly improve the gold plating uniformity.
3). Optimize the uniformity of gold plating:
(1)If the uniformity of gold plating is low, it will seriously affect the control of the thickness of gold plating in the production process. Reduce tank discharge
(2)If there is a big deviation in the grasp of time, insufficient dripping time will lead to a large amount of liquid in the tank, while too long dripping time will lead to the reduction of production efficiency and the waste of production capacity.
(3)At the same time, if the vibration device is added, the tank liquid attached to the plate surface can drip more quickly under the action of external forces, which can effectively reduce the amount of tank liquid taken out, and shorten the dripping time, increase the efficiency. At the same time, an auxiliary bracket is added on the drip bracket of the gold-plated groove to make the gold-plated fixture and the vertical direction become 45° Angle, which can accelerate the dripping of the tank liquid on the plate surface. Because when the production plate is normally hung, the whole edge of the lower end of the plate becomes the convergence point of adhesive groove liquid on the plate surface. When the plate is tilted, the liquid convergence point is at the corner of the plate, which can accelerate the liquid convergence and dripping on the plate. In order to optimize the uniformity of thick gold plating groove, it can be improved by changing the setting mode and position of titanium anode mesh in the groove, and the best solution can be found through technical test. At the same time, in the process of gold plating, for the relatively small production plate, can be equipped with anode baffle for production, can also significantly improve the gold plating uniformity.
