PCB Tech - Quality Control Method of Copper Immersion in Circuit Board Factory

Quality Control Method of Copper Immersion in Circuit Board Factory

Electroless Plating Copper is commonly known as sinking copper. Printed circuit board hole metallization technology is one of the keys to the printed circuit board manufacturing technology of the circuit board factory. Strictly controlling the quality of the hole metallization is the prerequisite to ensure the quality of the final product, while controlling the quality of the copper-immersion layer is the key. The commonly used test control methods are as follows:

1. Determination of electroless copper deposition rate:

The circuit board factory uses electroless copper plating solution, which has certain technical requirements for the copper sinking rate. If the rate is too slow, it may cause holes or pinholes in the hole wall; while the rate of copper sinking is too fast, and the plating layer will be rough. For this reason, scientific determination of the copper sinking rate is one of the means to control the quality of copper sinking. Taking the electroless thin copper plating provided by Schering as an example, introduce the method of measuring the copper sinking rate:

(1) Material: Epoxy base material after copper etching is used, the size is 100*100 (mm).

(2) Measurement steps: A. Bake the sample at 120-140 degree Celsius for 1 hour, then use an analytical balance to weigh W1(g); B. At 350-370 g/L chromic anhydride and 208-228 ml/L sulfuric acid Corrosion in the mixed solution (temperature 65°C) for 10 minutes, rinse with clean water; C. Treat it in the chromium removal waste liquid (temperature 30-40°C) for 3-5 minutes, and wash it clean; D. Pre-soak according to the process conditions, Activation and treatment in reducing solution; E. Copper sinking in copper sinking solution (temperature 25°C) for half an hour, and then cleaning; F. Bake the test piece at 120-140°C for 1 hour to constant weight, weighing W2(g) .

(3) Calculation of copper sinking rate: rate=(W2-W1)104/8.93*10*10*0.5*2(μm)

(4) Comparison and judgment: Compare and judge the measurement result with the data provided by the process data.

2. Method for measuring etching rate of etching solution

The circuit board factory performs micro-etching treatment on the copper foil before the through-hole plating to make the microscopic roughness to increase the bonding force with the copper sinking layer. In order to ensure the stability of the etching solution and the uniformity of the copper foil etching, the etching rate needs to be measured to ensure that it is within the specified range of the process.

(1) Material: 0.3mm copper clad laminate, degreasing, brushing, and cutting into 100*100 (mm);

(2) Measurement procedure: A. The sample is corroded in hydrogen peroxide (80-100 g/L) and sulfuric acid (160-210 g/L) at a temperature of 30°C for 2 minutes, and then cleaned with deionized water; B. At 120 Bake at -140 degree Celsius for 1 hour, weigh W2(g) after constant weight, and weigh W1(g) under this condition before the sample is corroded.

(3) Etching rate calculation rate=(W1-W2)104/2*8.933T(μm/min)

Where: s-sample area (cm2) T-etching time (min)

(4) Judgment: The corrosion rate of 1-2μm/min is appropriate. (Etch 270-540mg of copper in 1.5-5 minutes).

3. Glass cloth test method

In the process of hole metallization, activation and copper immersion are the key processes of electroless plating. Although the qualitative and quantitative analysis of ionic palladium and reducing solution can reflect the activation and reduction performance, the reliability is not as good as the glass cloth test. The copper sinking conditions in glass cloth are the most demanding, and it can best show the performance of activation, reduction and copper sinking liquid. The brief introduction is as follows:

(1) Material: Desizing the glass cloth in 10% sodium hydroxide solution. And cut it into 50*50 (mm), remove some glass filaments at the end of the circumference, so that the glass filaments are scattered.

(2) Test procedure: A. Treat the sample according to the copper immersion process;

B. Put it in the copper sinking liquid, the end of the glass cloth should sink completely after 10 seconds, and it will be black or dark brown. After 2 minutes, it will sink completely, and the copper color will deepen after 3 minutes; for heavy copper, 10 seconds The end of the back glass cloth must be completely copper-immersed, and after 30-40 seconds, all copper-immersed;

C. Judgment: If the above copper sinking effect is achieved, it indicates that the activation, reduction and copper sinking performance is good, but the opposite is poor.