PCB manufacturing electroplating technology: Immersion copper quality control method

Chemistry PlatingCopper (Electroless Plating Copper) is commonly known as sinking copper. Printed circuit board hole metallization technology is one of the keys to the manufacturing technology of printed circuit boards. Strictly controlling the quality of 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 the rate of electroless copper deposition

The use of electroless copper plating solution 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 sinking rate of copper 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. Take the electroless thin copper plating provided by Schering as an example, and introduce the method for measuring the copper sinking rate:  

(1) Material

The epoxy substrate after copper etching is used, and the size is 100×100 (mm).     

(2) Measurement steps

A. Bake the sample at 120-140℃ for 1 hour, then use an analytical balance to weigh W1(g); 

B. Corrosion in a mixture of 350-370g/L chromic anhydride and 208-228ml/L sulfuric acid (temperature 65℃) for 10 minutes, rinse with water;     

C. Treat it in the chromium removal waste liquid (temperature 30-40℃) for 3-5 minutes, and wash it clean;     

D. Pre-impregnation, activation, and treatment in reducing solution according to the process conditions;    

E. Sink the copper in the copper immersion liquid (temperature 25℃) for half an hour and clean it;     

F. Bake the test piece at 120-140℃ for 1 hour to constant weight, and weigh W2(g).     

(3) Calculation of copper sinking rate

Speed=(W2-W1)104/8.93×10×10×0.5×2(μm)    

(4) Comparison and judgment

Compare and judge the results of the measurement with the data provided by the process data.

2 Measuring method of etching rate of etching solution 

Before the through-hole plating, the copper foil is micro-etched to make the microscopic roughness to increase the bonding force with the copper sink 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. Bake at 120-140℃ 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 

Speed=(W1-W2)104/2×8.933T(μm/min)    

In the formula: s-sample area (cm2)  T-etching time (min) 

(3) Judgment

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

3 Test method for glass cloth 

In the process of hole metallization, activation and copper immersion are the key processes of electroless plating. Although qualitative and quantitative analysis of ionized palladium and reducing solution can reflect the activation and reduction performance, the reliability is not as good as the glass cloth test. In the glass cloth, the copper sinking conditions 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 steps:  

A. Process 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 thick copper, After 10 seconds, the end of the glass cloth must be completely coppered, and after 30-40 seconds, all copper should be sinked.

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