Analysis and improvement of oxidation problem of PCB gold plate

In view of the common adverse gold plate oxidation problems in the circuit board industry, including quality, process and so on, the oxidation of PCB gold board was analyzed, and the following improvement measures were implemented after discussion

Description of oxidation of sunk gold plate:

The oxidation of sunken gold plate is the contamination of the gold surface by impurities. The impurities attached to the gold surface change color after oxidation, which leads to the oxidation of the gold surface. In fact, the statement of gold surface oxidation is not accurate, gold is an inert metal, under normal conditions will not occur oxidation, and impurities attached to the gold surface such as copper ions, nickel ions, microorganisms in the normal environment easy oxidation metamorphism to form gold surface oxide.

Through observation, the main characteristics of gold plate oxidation are as follows:

1, improper operation causes pollutants to adhere to the gold surface, such as: with unclean gloves, finger cover contact with gold surface, gold plate and unclean table, plate contact pollution; This kind of oxidation area is large, may appear at the same time in the adjacent multiple pads, the appearance of light color is easier to clean.

2, poor water quality leads to impurities in the water adsorption on the gold surface, such as: gold after washing, finished product washing machine washing, such oxidation area is small, usually appear in the corner of the individual welding plate, is more obvious water stains; Water droplets will be retained on the welding pad after washing the gold plate. If the water contains more impurities, the water droplets will quickly evaporate and shrink to the corner of the plate at a higher temperature, and the impurities will be solidified in the corner of the pad after water evaporation; The main pollutants in washing after sinking gold and washing by finished plate washing machine are micro-bacteria. Especially, the tank using DI water is more suitable for fungus reproduction. The best test method is to touch the dead corner of the tank wall with bare hands to see if there is a smooth feeling.

3, half plug hole, through the hole near a small range of oxidation; This kind of oxidation is due to the potion in the hole or half-plugged hole is not cleaned or the residual water vapor in the hole, the potion in the storage stage of the finished product slowly diffused along the hole wall to the gold surface to form dark brown oxide.

4, the analysis of customer returns board, found that the gold surface density is poor, nickel surface has slight corrosion phenomenon, and the oxidation contains abnormal element Cu, the copper element is very likely due to the poor density of gold nickel, copper ion migration, such oxidation removal, still grow out, there is a risk of oxidation again.

Countermeasures to improve the anomaly:

The wall of the washing tank of the board raising tank and the finished product cleaning machine in the gold smelting site is dirty, and the wall of the washing tank has an obvious feeling of greasy when you touch it by hand.

1. The tank wall has the feeling of greasy, indicating that the tank wall has mold should be replaced with water every shift of small maintenance, a week of maintenance, maintenance is needed to soak the tank with hydrogen peroxide (2-5%) + sulfuric acid (3%).

2. Connect the water of the nickel gold washing machine to the water inlet before the gold sinking

3. The separate DI water pipe shall be cleaned once a month, and the cleaning plan shall be laid out by the Ministry of Environmental Protection

The last wash of the gold washing plate line is hot water, and the temperature of the plate is high before blowing dry. Hot water washing is easy to cause water stains. The first wash of the washing plate line should be changed to hot water and the last wash to cold water.

4. After sinking gold, the gold board is not cleaned in time and placed in the air for a long time

Adopt the principle of first out first washing, the time of the margin board waiting for cleaning in the air is not more than ten minutes, and the board in the groove of the board is not more than 30 minutes

5. Some oxidized board are half plugged holes or through holes

The oxidation phenomenon in the position of the half plug hole is caused by the residual potion in the hole. When cleaning, there will be BGA intensive facing down, reducing the speed of washing plate, and increasing the frequency of ultrasonic wave appropriately

6. In addition, the DI water storage tank and water supply pipeline should be cleaned with hydrogen peroxide and sulfuric acid once every quarter