Pretreatment before electroplating

INTRODUCTION

Electroplating is an electrochemical process which deposits metal onto a surface from an electroplating bath. A non-metal or non-conductive surface is first covered by a thin layer of metal before electroplating begins. This layer, or pre-treatment, is a crucial step in the electroplating process, as it prepares the surface to accept the metal being plated. This paper reviews the pre-treatment processes that can be used prior to electroplating, including acidic etching, alkaline etching, and mechanical surface preparation. We also provide an overview of the main differences in time, cost, and surface finishes achievable with each method.

ACIDIC ETCHING

Acidic etching, also known as acid pickling, is the most commonly used pre-treatment in electroplating. It involves immersing the object to be plated in a bath of strong acid, which chemically reacts with the surface to remove any impurities or oxidation. The acid removes the surface contaminants, leaving a uniform and smooth substrate for the electroplating to adhere to.

Acidic etching is usually a quick process, with the time required for the pre-treatment depending on the type and concentration of the acid used. It is also cost-effective and typically results in a consistent and reliable finish.

ALKALINE ETCHING

Alkaline etching is a similar process to acidic etching, but uses a bath of strong alkaline solution instead of acid. The alkaline solution is stronger than acid, but takes longer to etch the surface, as the reaction takes place slowly over time.

Alkaline etching can produce a finer finish than acidic etching, as it removes the top layer of the substrate more slowly and evenly. However, it is more expensive than acidic etching, and requires specialist equipment to use safely.

MECHANICAL SURFACE PREPARATION

Mechanical surface preparation is a physical process which removes unwanted materials from the surface of the object to be plated, rather than using a chemical reaction. The process typically involves using abrasives, such as grit paper, or manual abrasion techniques, such as brushing, to remove any dirt, oil, or rust.

Mechanical surface preparation is the most time-consuming pre-treatment, as the process must be repeated in order to achieve a satisfactory finish. It is also relatively expensive, as it requires specialist machinery, such as tumblers or sand-blasters, and the use of additional abrasive materials.

CONCLUSION

This paper has discussed the three most commonly used pre-treatment processes in electroplating: acidic etching, alkaline etching, and mechanical surface preparation. Acidic etching is the quickest, cheapest, and most reliable process, while alkaline etching can produce a finer finish. Mechanical surface preparation is the most time-consuming and expensive process, although with careful use, it can produce the smoothest surface finishes of all. When considering which process to use, it is important to consider the budget, time constraints, and desired surface finish.

Electroplating pretreatment is a process to pretreat the metal surface before electroplating. Through this process, the metal surface is cleaned and activated, in order to obtain uniform, dense and fine electroplated coating.

The pretreatment of the surface of the workpiece before electroplating includes degreasing, pickling, activation, etc. And these processes should be carried out in sequence, as these processes determine the future performance of electroplated metal parts.

The degreasing process is to remove the dirt such as oil and wax on the surface of the workpiece. The removal of these can make the subsequent electroplating steps more effective. Common degreasing agents include alkali aqueous solution, emulsified solution and solvent cleaning agents.

Pickling is a chemical treatment process that slowly dissolves metal oxides and other contaminants. It can make the effect of electroplating adhere to the metal surface more tightly, and also make the surface of the metal surface smooth and reflective.

Activation is a process of making the metal surface more reactive, which can help the metal molecules adsorb the molecules of the electroplating solution to form a more uniform and dense plating layer. Commonly used activation agents are chromic acid, sulfuric acid, sulfonated oil passivation solution (ROHS cleaner) and ammonium bifluoride passivation solution.

After the pretreatment process, electroplating can be carried out on the surface of the workpiece. If these processes are not completed correctly, it will lead to problems such as uneven plating thickness, poor adhesion, short plating cycle, etc.