PCB Technical - Methods to reduce gold salt consumption in PCB gold plating

Briefly introduce the method to reduce the consumption of gold salt in the gold plating process of PCB circuit board.

PCB is a printed board that connects dots on a common base material according to a predetermined design, and has been widely used in various electronic circuit components. PCB surface treatment can ensure the solderability of the printed circuit board during subsequent assembly and use. In addition to the basic requirements of welding and bonding strength, the surface treatment process also needs to meet some special requirements of customers for products, such as appearance, color, corrosion resistance, oxidation resistance, etc.

With the continuous development of PCB technology,customers have gradually increased the line width and line spacing requirements of printed circuit boards, and at the same time, the plating layer is required to have better reliability on the substrate. With the gradual rise of surface mounting technology for printed circuit boards, the connection pads and soldering pads of printed circuit boards are required to have good coplanarity and flatness.

In order to meet the development requirements of SMT, various manufacturers continue to innovate and improve the surface treatment technology of printed circuit boards, including electroplating technology. The gold layer has the characteristics of corrosion resistance, high conductivity, good weldability, low and stable contact resistance, high temperature resistance, softness, and wear resistance. At the same time, gold and other metals (such as Co, Ni, Fe, In, Cd, Ag, Cu, Sd, Pd, etc.) are easily alloyed, and after alloying, the hardness is higher and the wear resistance is better.

However, as the market price of gold has risen, the cost of gilding has become a key concern for enterprises. This subject mainly reduces the consumption of gold salt and saves the cost of gold plating by optimizing the gold plating process parameters, controlling the thickness of the gold plating layer, improving the uniformity of the gold plating and controlling the dripping time.

The gold salt consumption of electroplating gold wire mainly includes the consumption of the gold layer of the printed circuit board pattern and the consumption of the bath liquid. If the gold plating layer is too thick or the amount of bath solution is too much, it will cause the waste of gold salt and cause the cost of ineffective gold salt consumption.

Gold plating thickness control

At present, the thickness of the gold-plated layer is mainly controlled by the requirements of the production instructions and remarks, and there is almost no control over the upper limit of the thickness of the gold-plated layer. In view of this status quo, internal gold plating thickness control standards can be formulated. Relevant departments signed an internal contact form for the control of the thickness of the gold-plated layer to effectively control the upper limit of the thickness of the gold-plated layer within the scope of equipment and technical capabilities without affecting the quality of the production board.

Process parameter control

1 Potion stability control

The stability of the potion is a decisive factor affecting the rate of the gold plating reaction. As the main consumption component of the gold plating reaction, the concentration of gold ions will also fluctuate with production consumption. The fluctuation of the gold salt concentration will in turn lead to the fluctuation of the gold plating reaction rate. Therefore, in order to ensure the stability of the gold plating reaction rate, the concentration of the gold salt in the gold bath must be maintained at a relatively stable level. Under the premise that the potion is stable, the setting and adjustment of the gold-plating parameters will be more accurate, and the thickness of the gold-plating layer will be more stable. In order to maintain the stability of the gold salt concentration in the gold tank, the following two points must be noted:

(1) Maintain the accuracy and completeness of production records;

(2) Maintain the timeliness of golden salt replenishment, and follow the principle of "small amounts and many times".

2 Standardization of parameter control

The interleaving production of bulk boards and batch boards requires the control of the production of the first board, the thickness of the gold plating layer of the batch board, and the process of adding gold salt.

3 Monitoring measures for the thickness of the gold-plated layer

In order to ensure the monitoring effect, the following monitoring measures are now formulated.

(1) Formulate the "Gold Salt Cost Saving Project Monitoring Table" in view of the content of the gold plating layer thickness control, formulate the "Gold Salt Cost Saving Project Monitoring Table" to control the completeness of production records, the timeliness of gold salt addition, and the thickness control of the first gold plating layer, The batch plate gold plating layer thickness control and parameter adjustment after adding gold salt are audited, and non-conforming items are analyzed and improved.

(2) The ERP gold-plated layer thickness data is improved. The gold salt consumption data derived from the current ERP system is partially incorrect and incomplete. The software requirement form must be submitted to the information center to complete the module to ensure that the gold salt consumption data is accurate and complete.

(3) Statistical analysis of the thickness data of the gold-plated layer

Export ERP gold-plated layer thickness data records every week, make statistics according to line type and gold-plated thickness requirements, analyze the implementation and stability of the gold-plated layer thickness control of each line, and analyze and improve abnormal points.

Optimize plating uniformity

If the gold plating uniformity of the thick gold wire is low, it will seriously affect the control of the thickness of the gold plating layer during the production process. In the production process, in order to meet the customer's minimum gold plating thickness requirements, the gold plating layer is often thicker, causing serious waste of gold salt. In order to optimize the uniformity of the thick gold plating bath, the improvement can be started by changing the setting method and position of the anode titanium mesh in the bath, and the best solution can be found through technical testing. At the same time, in the gold plating process, for relatively small production boards, anode baffles can be used for production, which can also significantly improve the uniformity of gold plating.

Reduce the amount of tank liquid carried out

If there is a big deviation in the grasp of time, insufficient dripping time will cause a large amount of tank liquid, and too long dripping time will cause a reduction in production efficiency and a waste of capacity.

At the same time, if the vibration device is added, the tank liquid attached to the plate surface can be dripped faster under the action of external force, which can effectively reduce the amount of tank liquid carried out, shorten the dripping time, and increase efficiency. At the same time, an auxiliary bracket is added to the drip bracket of the gold-plated tank to make the gold-plated fixture form a 45° angle with the vertical direction, which can speed up the dripping of the plate surface tank liquid. Because when the production board is normally hung, the whole edge of the lower end of the board becomes the convergence point of the tank liquid on the board surface. When tilted and hung, the liquid converging point is at the corner of the board, which can speed up the liquid converging and dripping on the board surface.

In summary, PCB factories should master methods to reduce gold salt consumption in PCB gold plating and reduce production costs.