Electroless Plating Copper quality control method

Electroless Plating Copper known as Plated Through Hole (PTH). Printed circuit board hole metallization technology is one of the keys to printed circuit board manufacturing technology. Strict control of the quality of the hole metallization is a prerequisite for ensuring the quality of the final product, while controlling the quality of the electroless plating copper is critical. The commonly used control methods are as follows:

1. Determination of the rate of electroless plating copper:

The use of electroless copper plating solution has certain technical requirements for the rate of electroless plating copper. If the rate is too slow, it may cause voids or pinholes in the walls of the hole, if too fast will result in rough plating. To this end, the scientific determination of the rate of eletroless plating copper is one of the means to control the quality of eletroless plating copper. Now, the method for measuring the rate of eletroless plating copper is introduced:

(1) Material: An epoxy substrate after copper etching, having a size of 100 × 100 (mm).

(2) Determination procedure:
A. The specimens are baked at 120-140°C for 1 hour, and then weighed W1 (g) using ananalytical balance;
B. At 350-370g/liter of chromium trioxide and 208-228 ml/liter of sulfuric acid mixture (temperature 65°C) corrode for 10 minutes, wash with water;
C. Treat in chrome removal waste liquid (temperature 30-40°C) for 3-5 minutes, wash clean;
D. Pre-dip, activation, reduction solution treatment according to the process conditions;
E. In electroless copper plating solution (temperature 25°C) immersion half an hour, clean;
F. The specimens are baked at 120-140°C for 1 hour to constant weight, and weighed W2 (g).

(3) Calculation of the rate of electroless plating copper: rate = (W2-W1) 104 / 8.93 × 10 × 10 × 0.5 × 2 (μm).

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

2. Etching solution etching rate measuring method

Before the plating through hole, the copper foil is micro-etched to coarsen the micro-layer to increase the bonding force with the copper-clad layer. In order to ensure the stability of the etching solution and the uniformity of the etching of the copper foil, the etching rate is measured to ensure that it is within the range specified by the process.

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

(2) Measurement procedure:
A. The specimens are etched in hydrogen peroxide (80-100g/liter) and sulfuric acid (160-210g/liter) at a temperature of 30°C for 2 minutes, wash, deionized water leaned;
B. After baking at 120-140°C for 1 hour, weighed W2 (g) after constant weight, and the specimens was weighed W1 (g) according to the condition before corrosion.

(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 etching rate of 1-2 μm/min is suitable. (1.5-5 minutes etch copper 270-540mg).

3. Woven glass test method

In the process of hole metallization, activation and electroless plating copper are the key processes of electroless plating. Although qualitative and quantitative analysis of ionic palladium and reducing solutions can reflect the activation reduction performance, the reliability is not comparable to the woven glass test. The most demanding conditions for copper in woven glass are the best performance of activation, reduction and copper immersion. The brief introduction is as follows:

(1) Material: The woven glass was destarch in a 10% sodium hydroxide solution. And cut into 50 × 50 (mm), remove some glass filaments at the end of the four sides, so that the glass filaments are scattered.

(2) Test procedure:
A. The specimens is treated according to the electroless plating copper process;
B. Placed in the copper plating solution, after 10 seconds, the end of the woven glass should be completely plating copper, show black or dark brown, all plated after 2 minutes, after 3 minutes the color is deepened;
C. Judgment: If the above effect of electroless plating copper is achieved, it means that the activation, reduction and plating copper performance is good, otherwise it is not good.