The relationship between the amount of etchback in the hole and the amount of surface etching 3.1.1 The amount of etchback in the hole

As shown in Figure 1, the plasma treatment hole under different time conditions. The plasma discharge power is 4kW. Fig. 1(a), Fig. 1(b), and Fig. 1(c) are processing times of 30min, 60min and 120min, respectively. Figure 1(d) is a cross-sectional view of the hole wall before plasma treatment after drilling. It can be found that the hole wall after drilling is relatively straight. It is difficult to see the size of the hole thickness from Figure 1(d). The quality of the drilled hole is better, and the hole thickness formed is small. It can be seen from Figure 1(a) that the resin layer between the glass fiber and the copper layer is recessed by 12.5mm. Figure 1(b) and Figure 1(c) increase the amount of etchback to more clearly reflect the etchback of the resin layer. The etched resin is the result of plasma etching. Since the energy of electrons and ions in the glow discharge plasma is relatively low, the plasma does not etch the glass fiber and copper foil. The relationship between the time of etchback in the hole and the amount of etchback is shown in Table 1, which is approximately proportional. v> Table 1 Relation between etchback time and average etchback time etchback time/min 30 60 120 etchback volume/mm 11.6 22.9 46.8 3.1.2 The amount of surface etching As shown in Table 2, it is the relationship between the amount of surface etching and the etching time obtained at the same position under the same conditions as in Figure 1. From Figure 1, we can find that the amount of surface etching is approximately proportional to the etching time in the first 120 minutes. 3.1.3 The relationship between the amount of etchback in the hole and the amount of surface etching v> Table 2 The relationship between surface etching time and etching amount Surface etching time/min 30 60 120 Etching amount/g 0.25 0.55 1.12 The above experimental results show that the amount of etchback in the hole and the amount of surface etching have a relatively obvious proportional relationship in the first 120 minutes. According to the experimental results, the proportional coefficient of the amount of etching in the hole in the first 120 minutes is k hole=0.386mm/min; the first 120 minutes The scale factor of the surface etching amount is k table=0.0089g/min; (The calculation of the above scale factor is the arithmetic average of the three points to the origin). Because the ratio coefficients of the two are obtained at the same position under the same conditions, we can find out the amount of etchback in the hole H and the amount of surface etching under this condition. (1) The meaning of the proportional constant of the above formula is: every time the surface of the 10cm × 10cm small plate is etched 0.0231g, the etchback in the hole will increase by 1mm. According to this relationship, we can use the weighing method to get the amount of surface etching at any position in the cavity under this condition, and then calculate the amount of etchback in the hole. 3.1.4 The relationship between the amount of etchback in the hole and the amount of surface etching under other conditions In order to see the amount of etchback in the hole more clearly, the following experiments have extended the etching stage time to 2h. Figure 2 shows the etchback in the plasma treatment hole for 2 hours under different power conditions (3kW, 4kW, 4.5kW). The plasma processing power of Figure 2(a) and Figure 2(b) is 3kW, Figure 2(c), Figure 2(d) the plasma processing power is 4kW, Figure 2(e), Figure 2(f) plasma The processing power is 4.5kW. From the figure, we can get a very intuitive law: as the power increases, the depth of pitting in the hole increases. By measuring the average value of the etchback data in the hole (take 5 holes for a total of ten sets of measurement data): the average value of the etch depth in the hole for the plasma processing power of 3kW is 26.54mm; the average value of the hole for the plasma processing power of 4kW is The average etch depth is 30.64mm; the average etch depth in the 4.5kW plasma processing power hole is 44.93mm; and the amount of surface etching on the FR-4 test board at the same position under the same conditions is different The surface etching volume with 3kW plasma processing power: 0.6607g; the surface etching volume with 4kW plasma processing power: 0.8121g; the surface etching volume with 4.5kW plasma processing power: 0.9679g; from the above-mentioned etchback volume and surface etching volume in the hole The relationship (1) can be calculated under the plasma treatment conditions of 3kW, 4kW and 4.5kW power, the proportional constants obtained are: 0.0249g/mm, 0.0265g/mm and 0.0215g/mm (see Table 3). From these proportional constants obtained under different power conditions, it can be found that the values of the proportional constants are not much different (because the measurement of the etching depth is done by the method of metallographic sectioning, it is obtained under the condition of 40 times, which will inevitably cause errors), also There is no special law, so we approximate that the proportional constant does not change with the power.