Copper sink quality control method

Electroless Plating Copper is commonly referred to as sink copper. Printed circuit board hole metallization technology is one of the key technologies of printed circuit board manufacturing technology. Strictly controlling the quality of the hole metallization is the prerequisite for ensuring the quality of the final product, and controlling the quality of the sinking copper layer is the key. Daily test control methods are as follows:

  1. Determination of copper deposition rate:

Using chemical copper plating bath, there are certain technical requirements for the copper sink rate. Too slow a rate may cause voids or pinholes in the walls of the holes; and too slow a rate of copper sinking will produce rough coatings. For this reason, the scientific determination of sink copper rate is one of the means to control the quality of sink copper. Take the electroless plating of copper provided by Schering as an example to introduce the measuring method of copper deposition rate:

(1) Material: Epoxy substrate after copper etching, with a size of 100×100 (mm).

(2) Assay procedure: A. Bake samples at 120-140°C 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 liquid (temperature 65°C) for 10 minutes, wash in clean water; C. Treat in the waste liquid of chromium removal (temperature 30-40°C) 3-5 minutes, wash clean; D. Prepreg according to the process conditions , activation, reduction in the treatment of the liquid; E. in the copper sink solution (temperature 25 °C) sinking copper for half an hour, clean; F. baking the sample at 120-140 °C for 1 hour to constant weight, weighing W2 (g) .

(3) Copper sink rate calculation: 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.

  1. Etching liquid etching rate measuring method

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

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

(2) Determination procedures: A. Samples were etched in hydrogen peroxide (80-100 g/l) and sulfuric acid (160-210 g/l) at a temperature of 30°C for 2 minutes, cleaned, and cleaned with deionized water; B. At 120 Bake at -140°C for 1 hour. After constant weight, weigh W2 (g). Samples are weighed and weighed (W1(g)) before and after corrosion.

(3) Calculation rate of etching rate = (W1-W2) 104/2×8.933T (μm/min)

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

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

  1. Glass cloth test method

In the hole metallization process, activation and sinking of copper are key processes for electroless plating. Although the qualitative and quantitative analysis of ionic palladium and the reducing solution can reflect the activation and reduction performance, the reliability is inferior to the glass cloth test. Copper sinking conditions are the most severe in glass cloths, and they can show the properties of activation, reduction, and copper sinking. The brief introduction is as follows:

(1) Materials: The glass cloth was deslized in 10% sodium hydroxide solution. And cut into 50 × 50 (mm), remove some glass fiber around the end, so that the glass filaments spread out.

(2) Test procedure: A. The sample is treated according to the copper sink process;

  1. Into the copper sink solution, 10 seconds after the end of the glass cloth should be completely filled with copper, black or dark brown, 2 minutes after all sink, copper color deepens after 3 minutes; thick copper, 10 seconds After the end of the glass cloth must be completely filled with copper, 30-40 seconds later, all sinking copper;
  2. Judgment: If the above copper sinking effect is achieved, it indicates that the activation, reduction, and copper sinking performance are good, and the anti-deposited copper is poor.

 Grace Zheng