Introduction of Immersion Gold Process Control for Multilayer Circuit Board

Introduction of Immersion Gold Process Control for Multilayer Circuit Board

Hello, everyone, I am the editor, today I will talk to you about the process control of multi-layer circuit board immersion gold, let’s take a look at it together.

1. Process introduction

The purpose of the gold-immersion process is to deposit a nickel-gold coating with stable color, good brightness, flat coating, and good solderability on the surface of the printed circuit. Basically, it can be divided into four stages: pre-treatment (degreasing, micro-etching, activation, post-dipping), immersion of nickel, immersion of gold, and post-treatment (washing waste gold, washing with DI water, and drying).

2. Pre-processing

The pretreatment of immersion gold generally has the following steps: degreasing (30%AD-482), micro-etching (60g/InaPS, 2%H2SO4), activation (10%Act-354-2), post-immersion (1%H2S04) ). To remove oxides on the copper surface, and sink palladium on the copper surface to act as an active center for nickel precipitation. If one of the links is not handled well, it will affect the subsequent nickel and gold deposits and lead to mass scrapping. During the production process, various syrups must be analyzed and supplemented regularly to control them within the required range. The more important ones are: the micro-erosion rate should be controlled at "25U-40U", a new tank must be opened when the copper content of the activated potion is greater than 800PPM, the cleaning and maintenance of the potion tank will also have a greater impact on the quality of the PCB. The rear immersion tank should be changed weekly, and each washing tank should also be cleaned weekly.

3. Immersion nickel

The main components of the nickel syrup are Ni²+ (5.1-5.8g/1), the reducing agent sodium hypophosphite (25-30g/1) and stabilizers. Because chemical nickel has strict requirements on the composition range of the syrup, it must be in the production process. Analyze and test twice per shift, and add Ni² reducing agent according to the bare copper area or experience of the production board. When adding materials, follow the principle of small amount and multiple times to prevent the local plating solution from reacting violently and causing the plating solution. Accelerated aging, PH value, and bath temperature have a greater influence on nickel thickness, and the temperature of nickel bath is controlled at 85℃-90℃. PH is between 5.3 and 5.7. When the nickel cylinder is not in production, the temperature of the nickel cylinder should be lowered to about 70℃ to slow down the aging of the plating solution. The electroless nickel plating solution is more sensitive to impurities, and many chemical components are harmful to chemical nickel, which can be divided into the following Several categories: inhibitors: including Pb.Sn..Hg.Ti.Bi (low melting point heavy metals), organic impurities include S², nitric acid and anionic wetting agents. All of these substances will reduce the activity, resulting in a reduction in the electroless plating speed and skip plating. When severely punished, the electroless nickel plating process will be completely stopped.

Organic impurities: In addition to the organic stabilizers mentioned above, there are plastic agents and impurities from equipment and solder. Although a part of impurities can be removed by continuous plating, it cannot be removed completely.

Unstable agent: Including Pd and a small amount of copper. These two components make chemical nickel unstable, which makes the coating rough and excessively plated on the tank wall and heater. Solid impurities: including calcium sulfate or calcium phosphate and other insoluble substances sinking into or brought into the solution. Filtration can remove solid particles.

In short: effective measures should be taken to reduce the mixing of such impurities into the plating solution during the production process.

Four, Immersion Gold

The gold immersion process is a gold immersion process, the main component of the immersion gold cylinder; Au (1.5-3.5g/l), the bonding agent is (Ec0.06-0.16mol/L), which can be replaced on the nickel-phosphorus alloy layer Pure gold plating makes the coating smooth and fine crystallized. The pH value of the plating solution is generally between 4-5, and the control temperature is 85°C-90°C.

Five, post-processing

Immersion gold post-processing is also an important link. For printed circuit boards, it generally includes: waste gold washing, DI washing, drying and other steps. If conditions permit, the immersion gold board can be further washed with horizontal washing. drying. The horizontal plane washing machine can be washed by chemical water (10% sulfuric acid, 30g/L hydrogen peroxide), high-pressure DI water washing (30~50PSI), DI water washing, drying, and drying sequence setting process to completely remove the printed circuit board holes and The surface is stained with syrup and water, and the plating layer is uniform and the immersion gold plate with good brightness is obtained.