Analytical Test Study of PCB Plating Solution (1)

one. Microscopic analysis

The microscopic analysis is to evaluate the coating thickness, stress, dispersion, inner layer connection of the multilayer board, side etching caused by etching, drilling quality and weldability. Microscopic analysis is an important part of PCB plating process control. The microsection profile is a special test section cut from a PCB diamond saw. This section is embedded in plastic, sanded, polished, and examined under a metallographic microscope. Most of the PCB's section cuts are carried out on metalized holes, and the above evaluation can be performed.

The specimen to be inlaid is diamond sawed or cut about 1/8 inch away from the edge of the hole or the edge of the hole. (If the conditions are better, the visible surface may be beveled at 45 or 30 degrees so that the visible surface will increase, and Take into account the dual nature of straight cuts and cross cuts). Most inlaid plastics, whether cold-cured or hot-studded, can be used. Inlaid plastic must be purchased with hot inlays. The choice of inlaid plastic will depend to a large extent on the composition of the sample material, the area to be examined and the quality of the inlay required for the inspection.

Once the sample has been inlaid, several processing steps are required for final inspection. These several processing steps can be summarized as coarse grinding, fine grinding, preliminary polishing and fine polishing. An 8-inch disc type electric polisher is generally used. Water is used during grinding to remove all debris. Electric grinders can be variable speed, low speed can be used for sanding, high speed can be used for polishing. The inlaid sample was first ground with a 60 grit abrasive disc until the hole was initially worn. Then use 180 grit sandpaper to completely break the hole. The sand was then ground to half with 320-grit sandpaper. Finally, deep scratches were removed with 600-grit sandpaper.

Early polishing uses a medium cotton lint cloth. For high-speed polishing, there should be a series of alumina polishing pastes on hand. During the entire polishing stage, the polishing cloth should be kept moist with a fine polishing liquid. A 1 micron alumina was used in the initial polishing stage followed by 0.3 micron alumina. For fine polishing, the polishing cloth should be removed and replaced with a micro polishing cloth. 0.05 micron alumina should be used as the polishing medium. The cut surface should be both smooth and bright.

In order to remove any grimacing that may cause erroneous discrimination on the cross-section, the following etchant is recommended for microetching in the above copper formulation:

Potassium dichromate 2 g water 100 ml sodium chloride (saturated solution) 4 ml concentrated sulfuric acid 12 ml

This is a micro-etching method during the dry period, which will make the tin and lead layers black. Now the copper surface obtained by the commonly used ammonia method is delicate and the tin-lead surface is still white. The formula is as follows:

5-10cc ammonia +45cc pure water +2-3 drops of hydrogen peroxide

After mixing evenly, use a cotton swab dipped in the etching solution, and gently wipe the surface of the slice after washing and drying for about 2-3 seconds. Note that bubbles may occur on the copper surface. After 2-3 seconds, immediately clean and dry with pure water and Toilet Paper. Do not allow the copper surface to continue to change color and oxidation. Instantaneous examination using a high-resolution microscope, sampling and preservation are necessary at this time to immediately save the photographic standard.

two. Analysis of PCB Plating Solutions

Using Patented Additives Most suppliers of PCB plating fluids provide analytical methods that they consider best suited to their own process. Usually the supplier will provide a Hull cell or similar cell test method, while also providing graphically illustrated individual issues. Before carrying out any electrolyzer test, during the production process (timing), analysis of the bath solution should be performed to ensure that the bath components are within the normal control range.

A. Analysis of tin-lead alloy plating solution

â– 1. Determination of Sn2+ in plating bath

1.1 Reagents

0.1N iodine solution;

1% starch indicator

20% sulfuric acid.

1.2 Analysis

Take plating solution mL, add 20% sulfuric acid 20 mL, add water 50 mL, use 0.1N iodine droplets, and titrate with starch as indicator until the blue color does not disappear.

1.3 Calculation of Tin Content in Bath:

Sn2+=NV1*0.059*1000/V(g/L)

In the formula:

The equivalent concentration of N-standard iodine solution;

V1 - Iodine solution consumption (mL) during titration;

V-sample volume (mL).

(to be continued)