Quality control method for copper deposition of PCB circuit board

Chemical copper plating (Electroless Plating Copper) is commonly called copper precipitation. The hole metallization technology of printed circuit board is one of the key technologies of printed circuit board manufacturing. Strict control of the quality of metallization is the premise to ensure the final product quality, and the quality control of the copper deposit is the key. The test control methods for daily use are as follows:


Determination of copper precipitation rate by 1. chemical method:


The electroless copper plating bath has certain technical requirements for copper deposition rate. The velocity is too slow, which may cause holes or pinholes in the hole wall; and the copper deposition rate is too fast, which will result in rough coating. Therefore, the scientific determination of copper deposition rate is one of the means to control the quality of copper deposit. To provide the chemical plating copper thin Schering as an example, method for the determination of copper deposition rate profile:


(1) materials: the copper matrix is 100 x 100 (mm).

(2) determination steps:

A. baked the sample at 120-140 degrees for 1 hours, and then weighed W1 (g) with analytical balance;

B. in 350-370 grams / liter 208-228 ml / L of chromic acid and sulfuric acid (temperature of 65 DEG C) corrosion for 10 minutes, wash with water;

C. was treated in the waste liquid containing chromium (temperature 30-40 C) for 3-5 minutes and cleaned;

D. pretreatment, activation, reduction solution treatment according to process conditions;

E. in the copper bath (temperature 25 degrees) copper for half an hour, clean;

F. samples were dried at 120-140 for 1 hours to constant weight, weighing W2 (g).

2. etching solution etching rate determination method

Before the hole plating, the copper foil is treated by micro etching to make the micro roughening, so as to increase the binding force with the copper deposit. In order to ensure the stability of etching solution and the uniformity of etching of copper foil, the etching rate should be measured to ensure that the process is within the specified range.

(1) material: 0.3mm copper clad laminate, degreasing, brush plate, and cut into 100 x 100 (mm);

(2) determination procedure:

A. samples were corroded in hydrogen peroxide (80-100 g / L) and sulfuric acid (160-210 g / L), temperature 30 degrees for 2 minutes, and cleaned and deionized water was cleaned;

B. was baked at 120-140 C for 1 hours and weighed W2 (g) after constant weight. The samples were weighed W1 (g) according to this condition before corrosion.

(3) etching rate calculation

Rate = (W1-W2) 104 / 2 x 8.933T (M / min)

Type: s- sample area (cm2) T- etching time (min)

(4) judgment: 1-2 m/min corrosion rate is appropriate. (1.5-5 minutes pitting copper 270-540mg).

Test method for 3. glass cloth

In the process of hole metallization, activation and precipitation of copper are the key processes of electroless plating. Although qualitative and quantitative analysis of ion palladium and reducing liquid can reflect the activation and reduction performance, the reliability is not comparable to that of glass cloth test. The most demanding condition for copper deposition in glass cloth is to show the performance of activation, reduction and copper precipitation. Here are the following:

(1) material: glass cloth in 10% sodium hydroxide solution for desizing treatment.  And cut into 50 x 50 (mm), around the end to remove some glass fiber, so that the glass fiber spread.

(2) test steps:

A. process the sample according to the copper deposition process;

B. into the sink copper solution, 10 seconds after the glass cloth ends shall be copper, black or dark brown, sunk in 2 minutes, 3 minutes of heavy copper deepens; copper, 10 seconds after the end of the glass cloth must sink copper completely, after 30-40 seconds, all sink copper.

C. judgment: if the above copper precipitation effect, indicating activation, reduction and copper precipitation performance is good, the inverse is poor.


 

(Source: internal information)

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