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Acid Electroplating Copper Technology

by: Dec 11,2018 383 Views 0 Comments Posted in Engineering Technical

Application of Acid Copper Plating in PCB Manufacturing:

After a series of processes, the printed circuit board needs to be metallized and deposited on the hole wall surface of the through hole in order to achieve the purpose of interconnection and intercommunication between the board and the board and to achieve strong conductivity. Taking into consideration, copper metal is regarded as the most extensive deposition material in the industry. At present, the process of hole metallization generally requires two steps: electroless plating and electroplating.

QQ图片20181212104514_副本.jpg

Electroless Plating:

Electroless plating is also called chemical copper precipitation. The principle of chemical precipitation of copper is shown in the equation (1-1), because the reaction is new· the copper atoms and hydrogen atoms generated can facilitate the reaction to continue to the right, so it is called self-catalyzed REDOX reaction.

image.png

The stand or fall of the electroless plating copper layer is the precondition of performance more excellent printed circuit board, so in the process of electroless plating pretreatment, must be strictly controlled experimental conditions and operation specification, such as time, temperature, solution of liquidity and water stage caused by inadequate solution pollution will directly affect the quality of the chemical sink copper. If the plating solution has poor fluidity, it may lead to poor uniformity of the copper layer and formation of copper layer cavity inside the through-hole, which brings great difficulties and challenges to subsequent plating procedures. Therefore, in the process of chemical precipitation of copper, we generally make the plate swing from side to side and use air pumping to enhance the fluidity of the plating solution.

QQ图片20181212104509_副本.jpg

Electroplating Technology:

We often use sulfate as the main system in copper acid electroplating industry. The following figure shows the principle of copper deposition in cupric acid electroplating system. We can see from the picture, due to the effect of dc power supply, image.pngof solution will move to the cathode in the directional, near the cathode image.png will get image.png form Cu, electrochemical reaction and formation of Cu electrocrystallization process happens adhere to the cathode surface and hole forming inside the plating copper layer. With the constant consumption of image.png in the solution, the image.pngof soluble anode itself will enter the solution and be supplemented to maintain the balance of image.png concentration in the plating solution. This kind of cyclic consumption at the cathode and anode and the formation of image.png can guarantee the smooth electroplating reaction.

image.png

During electroplating, the reaction of image.png takes place in roughly two steps. As shown in the reaction equations (1-2) and (1-3), the image.png initially get an image.png to form the image.png, followed by another image.png to form the Cu, which is deposited as the copper layer.

image.png


As the plating progresses, image.png in the solution will be consumed and their concentration will decrease. At this time, image.png that may exist due to insufficient oxidation will undergo hydrolysis reaction, as shown in equation (1-4).

image.png


When the acid concentration gradually decreases, the hydrolysis reaction will continue to move to the right and lead to the production of image.png. The image.png in the solution will slowly move to the cathode under the action of airflow and adsorb on the cathode plate surface to produce the so-called "burr". This will make the surface which plates copper rough and reduce the performance and quality of the PCB. Therefore, the concentration of acid image.png in the plating solution will be monitored and replenished in time to avoid the occurrence of this reaction.

In addition, the concentration and type of additives play a crucial role in copper acid electroplating system. They will cooperate and influence each other under the effect of current, change the current density of each field and jointly inhibit or accelerate the deposition of copper to control the growth rate of crystal nucleus, and then obtain uniform and meticulous electroplating surface. However, with the electroplating of additives, not only the cathode is consumed, but also an irreversible reaction with the anode, resulting in a sharp change in additive concentration, which affects the quality and performance of the cathode plate. Therefore, the industry will also monitor the consumption speed and consumption of additives in real time, and give supplements in a timely manner to ensure the successful completion of electrochemical copper deposition.

QQ图片20181212104454_副本.jpg


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