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Electroless plating copper is commonly known as PTH. The hole metallization technology of printed circuit board is one of the keys of the manufacturing technology of printed circuit board. Strictly controlling the quality of hole metallization is the premise to ensure the quality of final products, while controlling chemical copper plating rate.

1. Determination of chemical copper precipitation rate:

Using chemical copper plating solution, there are certain technical requirements for PTH rate. Too slow rate may cause holes or pinholes in the hole wall; If the PTH rate is too fast, the coating will be rough. Therefore, scientific determination of PTH rate is one of the means to control the quality of PTH. Taking the electroless plating of thin copper provided by Xianling as an example, the determination method of PTH rate is briefly introduced:

(1) Materials

The epoxy base material after copper corrosion is used, and the size is 100 × 100(mm)。     

(2) Measurement steps

1. Bake the sample at 120-140 ℃ for 1 hour, and then weigh W1 (g) with an analytical balance;  
2. Corrosion in the mixture of 350-370 g / L chromic anhydride and 208-228 ml / L sulfuric acid (temperature 65 ℃) for 10 minutes, and clean with water;     
3. Treat it in the waste liquid of chromium removal (temperature 30-40 ℃) for 3-5 minutes and wash it clean;     
4. Pre dip, activate and treat in reducing solution according to the process conditions;     
5. Sink copper in copper precipitation solution (temperature 25 ℃) for half an hour and clean it; Bake the test piece at 120-140 ℃ for 1 hour to constant weight, and weigh W2 (g).   

(3) Calculation of PTH rate

Rate = (w2-w1) 104/8.93 × 10 × 10 × 0.5 × 2( μ m)    

(4) Comparison and judgment

Compare and judge the measured results with the data provided by the process data.

2. Determination method of etching rate of etching solution:

Before through-hole plating, the copper foil is micro etched to coarsen the microstructure, so as to increase the adhesion with the PTH layer. In order to ensure the stability of the etching solution and the uniformity of copper foil etching, it is necessary to measure the etching rate to ensure that it is within the range specified by the process.     

(1) Materials

0.3mm copper clad foil, degreased, brushed, and cut into 100 × 100(mm);     

(2) Determination procedure

1. The sample is corroded in hydrogen peroxide (80-100 g / L) and sulfuric acid (160-210 g / L) at 30 ℃ for 2 minutes, and then cleaned with deionized water;  
2. Bake at 120-140 ℃ for 1 hour, weigh W2 (g) after constant weight, and weigh W1 (g) before corrosion.     

(3) Etching rate calculation

Rate = (W1-W2) 104/2 × 8.933T( μ m/min)    

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

(4) Judgement

1-2 μ m/min corrosion rate is appropriate. (270-540mg copper corrosion in 1.5-5 minutes).

3. Glass cloth test method:

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

(1) Material:

The glass cloth is desized in 10% sodium hydroxide solution. And cut it into 50 × 50 (mm), remove some glass filaments at the ends around to spread the glass filaments.     

(2) Test steps:

1. Treat the sample according to the copper precipitation process procedure;  
2. Put it into the copper precipitation solution. After 10 seconds, the end of the glass cloth should be completely sunk in copper, black or dark brown. After 2 minutes, it should be completely sunk, and after 3 minutes, the copper color will deepen; For heavy copper, the end of the glass cloth must be completely sunk after 10 seconds, and all copper must be sunk after 30-40 seconds.
3. Judgment: if the above copper precipitation effect is achieved, it indicates that the activation, reduction and copper precipitation performance is good, but on the contrary, it is poor.