PCB Tech - PCB material classification and silver plating introduction

1. PCB material classification

There are 3 types according to metal materials. Typical PCB displays are divided into 3 types according to soft and hard structures. Typical PCB copy boards and electronic plug-ins are also suitable for high pin count, miniaturization, SMD and complex development.

The electronic plug-in is mounted on the circuit board and soldered to the other side through a pin. This technology is called tht (Through Hole Technology) plug-in technology. In this way, each foot is drilled on the PCB board to illustrate the typical application of the PCB. With the rapid development of SMT patch technology, guidance is needed between multilayer circuit boards, and various drilling equipment is required to ensure this through drilling after plating.

In order to meet the above requirements, at present, PCB CNC drilling equipment with different performance is introduced at home and abroad.

The production process of printed circuit boards is a complex process, involving a wide range of processes, mainly involving photochemistry, electrochemistry, and thermochemistry. There are more process steps involved in the manufacturing process. Take hard multilayer circuit boards as an example to illustrate the processing process. . Drilling is a very important process in the whole process, and the processing time of the hole is the longest.

The position accuracy of the hole and the quality of the hole wall directly affect the subsequent hole metalization and patching processes, and also directly affect the processing quality of the printed circuit board. The principle of machining cost CNC drilling machine,

Commonly used methods for drilling structure and function on circuit boards are numerical control mechanical drilling method and laser drilling method. At this stage, most of the mechanical drilling methods are used. With the popularity of high-density laminated circuit boards, the demand for blind holes has increased, and the application of laser drilling methods has increased momentum.

However, the laser drilling process has poor adaptability to processed materials, high equipment costs, and low hole wall quality. Now mechanical drilling machines have achieved nearly 90% of PCB holes. In order to improve efficiency and reduce costs, the PCB duplication drilling machine adopts a multi-axis parallel cascade structure. At present, the most widely used is the six-axis drilling machine. The main body is a frame gantry structure, which is divided into: basic components bed, beam, x-axis, y-axis and z-axis motion guide components, worktable components, spindle components, and other auxiliary functional components.

The main movement of the PCB drilling machine is the x-y-z three-axis linear movement and the high-speed rotational movement of the main shaft. Because drilling is generally controlled by points on the x and Y axes, the movement and positioning of the x and Y axes are generally high-speed positioning, while the z axis is a direct working axis, and different feed speeds need to be adjusted and controlled according to the size of the hole. Through the combination of the above motions and some auxiliary functions, through holes and blind holes of different apertures can be processed at different positions on the PCB board, and the accuracy and speed of the PCB board reading and drilling machine can also be determined, such as the main parameters.

2. Introduction of PCB Chemical Silver Plating

Methanesulfonic acid was selected as the acid system of electroless silver plating, and the influence of main salt, various additives and related process conditions on the thickness and quality of the coating was investigated. The results show that when the AgNO3 concentration is 2.5g/L, the mass fraction of methanesulfonic acid is 12%, and the reaction time is 5min, the resulting coating is uniformly silver-white and bright with a thickness of 0.16μm.

This process is suitable for soldering on printed circuit boards (PCB). And using atomic force microscope to detect the surface morphology of the coating to investigate some factors that affect the quality of the coating.

The final process of printed circuit board (PCB) manufacturing is to perform solderability treatment on the surface. The silver layer has good solderability, weather resistance and electrical conductivity. The use of replacement electroless silver plating can improve the defects in the hot air leveling process that is widely used today, and meet the society's requirements for high technology and environmental friendliness.

Methanesulfonic acid acid system has been used in other aspects of electroless plating, but reports on electroless silver plating are extremely rare. It can improve the stability of the formula, facilitate the adjustment of acid value and the treatment of waste water.

In this experiment, methanesulfonic acid was used as the acidic system of electroless silver plating. The suitable process conditions of the system were studied through single factor experiment, and it was expected to obtain a silver-white bright plating layer with a thickness of more than 0.15μm. And use atomic force microscope, thickness gauge and other instruments to detect the coating.

PCB silver plating process

Sample-Chemical degreasing-Two washings-Pickling (micro-etching)-Distilled water washing-Pre-soaking-Chemical silver plating-Water washing-Blow-drying.

Plating solution preparation

1) Prepare 200mL of 10g/L AgNO3 solution and store it in a brown bottle for later use; dilute 70% of the copy plate methanesulfonic acid to 30% to prepare 250mL for use; prepare a certain concentration of additives including propylene thiourea, thiourea, Polyethylene glycol 600, polyethylene glycol 6000, urea, ammonium citrate, citric acid, OP emulsifier, ammonia, ethanol, and some additives can be copied for use.

2) Take a beaker with a volume of 100 mL, and use a pipette to take methanesulfonic acid, various additives and AgNO3 solutions to prepare a silver plating solution.

3) When a certain additive is tried, it can be prepared immediately, and the effect on the surface of the coating can be observed through comparative tests to determine its effect in the plating solution.

4) Prepare 100mL silver plating solution, adjust the pH to about 1 at room temperature, immerse the pretreated copper sheet in it, control the reaction time, generally 10-15min, visually observe that the copper sheet is covered by the silver layer The macroscopic phenomena such as speed, uniformity, brightness, surface impurities, and coverage area should be recorded in detail.