Due to the rapid development of electronic technology, the printed circuit technology continues to develop. PCB board has developed from single side to double side to multi-layer, and the proportion of multi-layer board is increasing year by year. Multilayer board is developing in the direction of high, fine, dense and fine. Lamination is an important process in multi-layer board manufacturing. The control of lamination quality is becoming more and more important in multi-layer board manufacturing. However, it is impossible not to encounter problems in the actual manufacturing process.

 

 

 

In the lamination process of PCB multilayer board, due to various reasons, there will be a variety of different degrees of defects. If not well controlled, it will bring a lot of quality problems to the circuit board, some of which will even lead to the scrapping of the whole circuit board. So, in detail

 

The analysis of the main problems in the whole lamination process will be helpful to understand the main causes and improve the quality of the products. Through the practice in the workshop, the author found some problems in the lamination process of the company and put forward relevant solutions.

 

 

 

1. Lack of glue or resin content

 

a. Form of expression: the appearance is white, showing the glass fabric texture

 

        b. Reason:

 

① The resin flows too fast, resulting in the lack of glue in the pressing part

 

② If the temperature rises too fast and too high, the hygroscopicity of the multilayer board will increase, resulting in white spots and texture exposure in the later process (such as green oil)

 

③ Too many PP sheets and layers

 

4. The adhesive film has low resin content, long gel time and large fluidity.

 

 

 

c. Solution:

 

① Reduce the temperature and pressure of lamination

 

② Adopt the most reasonable laminate parameters, such as the number of p-sheets, the number of layers each time

 

③ During lamination, carefully observe the resin flow, pressure change and temperature rise, and adjust the start time of applying high pressure

 

 

 

2. Bubbles or bubbling

 

a. Manifestation: the appearance of small bubble clusters or limited bubble accumulation or layer to local separation

       b. Reason:

 

 

 

① Low pre pressure

 

② The temperature is too high and the interval between pre pressure and full pressure is too long

 

③ The content of volatiles in PP tablets was high

 

④ The surface of pressing surface is not clean, mainly including inner surface pollution and foreign material pollution

 

 

 

c. Solution:

 

 

 

① The relationship between temperature and fluidity is coordinated

 

② Reduce the preloading cycle and reduce the speed of temperature rise, reduce the volatile content

 

Strengthen the cleaning operation, such as avoiding touching the effective area of PP sheet in the process of plate arrangement, P sheet must be used up within 15 minutes after being removed from the vacuum drying environment, etc

 

 

 

3. Warping

 

a. Expression form: board surface or board edge warping

 

 

 

b. Reason:

 

① Inner laminates or prepreg from different manufacturers are used

 

② The warp and weft directions of the core board and the prepreg are not consistent when arranging the boards

 

③ The internal stress in the plate is too large after pressing

 

 

 

c. Solution:

 

1. The arrangement of the prepreg between the layers of the multilayer board should be symmetrical. For example, for the six layer board, the thickness between 1-2 and 5-6 layers should be consistent with the number of prepreg sheets, otherwise it is easy to warp after lamination.

 

2. The products of the same supplier shall be used for the core board and the prepreg.

 

3. After laminating, the shrinkage of the cured sheet in warp and weft directions is different. It is necessary to distinguish the warp and weft directions when cutting and arranging. Otherwise, it is easy to cause warpage after lamination, and it is difficult to correct even if the pressure is applied. Many of the reasons for the warpage of the multilayer board are that the warp and weft directions of the prepreg are not distinguished during lamination, and the prepreg is randomly discharged.

 

4. After hot pressing and cold pressing, the multilayer board is taken out, the rough edges are cut or milled off, and then the multilayer board is placed flat in the oven at 180 ℃ for 4 hours, so as to gradually release the stress in the board and completely cure the resin.

 

 

 

4. Pinhole of copper foil

 

a. Manifestation: some small pinholes appear on the copper foil

 

① The steel plate used for pressing is not smooth

 

② The board surface garbage is not cleaned up, such as dust, etc

 

 

 

c. Solutions

 

1. The steel plate is required to be polished every time it is pressed, because there may be resin flowing to the steel plate. If it is not polished, the next pressing plate may cause pits or pinholes, so it needs to be polished every time it is pressed

 

2. Pay attention to clean the plate surface when arranging the plate. If the cleanliness is not enough, dust and other debris will fall into the interlayer or copper foil, resulting in dents or pinholes

 

 

 

4. The influence of lamination process on inner circuit

 

Performance: inner open circuit and short circuit

 

Analysis: when laminating, the positioning pin or positioning hole must be used for positioning. If the pressure used in mounting is not uniform, the positioning hole of the inner layer board will be deformed, and the residual stress caused by excessive pressure in pressing is also great. In addition, the deformation of the upper layer will cause the dislocation of the inner layer of the multilayer printed circuit board and lead to short circuit or open circuit, which will eventually lead to failure Leading to the scrapping of the board.

 

 

 

Conclusion: This paper finds out the quality defects in the manufacturing process and analyzes the root causes, and then takes corresponding process countermeasures to solve these defects, so as to achieve the purpose of improving product quality. Due to the limited time and the author's ability, this paper can not exhaust all the problems in the lamination process, and there will inevitably be some shortcomings in the article, which will be my future work should strive to learn and improve.