1. Laminate Structure
Cutting → inner layer → inner layer etching → inner layer AOI test → browning → pressing → one-time drilling → immersion copper → panel plating → outer layer circuit → outer layer etching → outer layer QC inspection → outer layer AOI → immersion copper → board electrical → outer circuit → outer layer etching → outer QC inspection board → outer layer AOI → solder mask pretreatment → solder mask → characters → lead-free spray tin → routing → electrical test → FQC → packaging
3. Manufacturing difficulties
Heavy copper PCB has a series of processing difficulties due to the heavy copper thickness, such as the need for multiple etchings, insufficient filling of the board pressing, cracking of the inner layer of the drilled hole, and difficulty in guaranteeing the quality of the hole wall.
a. Difficulties in etching
As the copper thickness increases, due to the increasing difficulty of potion exchange, the amount of side erosion measured will become larger and larger; in order to reduce the amount of side erosion caused by potion exchange as much as possible, multiple rapid etchings are required. The method solves the problem. As the amount of side erosion increases, it is necessary to increase the etching compensation coefficient to compensate for the side erosion.
b. Difficulties in lamination
With the increase of copper thickness, the line gap is deeper. In the case of the same copper residual rate, the required amount of resin filling needs to be increased. You need to use multiple prepregs to meet the filling problem; because you need to use resin to maximize The filling line gap and other parts, the glue content is high, and the prepreg with good resin fluidity is the first choice for heavy copper PCB. The commonly used prepregs are 1080 and 106. In the inner layer design, copper points and copper blocks are laid in the copper-free area or the final milled area to increase the residual copper rate and reduce the pressure of filling.
The increase in the amount of prepreg used will increase the risk of sliding, and the method of adding rivets can be used to strengthen the degree of fixation between the core boards. Under the trend of increasing copper thickness, resins have also begun to fill the blank areas between patterns. Since the total copper thickness of heavy copper PCB is generally above 205.8um (6 oz), the CTE matching between the materials is particularly important (for example, the CTE of copper is 0.0017% (17ppm), and the glass fiber cloth is 0.0006%-0.0007% (6ppm). -7ppm), the resin is 0.02%]. Therefore, in the PCB processing process, the choice of fillers, low CTE and high Td boards is the basis for ensuring the quality of heavy copper boards.
As the copper is thicker than the board thickness, more heat is required for lamination. The actual heating rate will be slower, and the actual duration of the high-temperature section will be shorter, which will result in insufficient resin curing of the prepreg, which will affect the reliability of the board; therefore, it is necessary to increase the duration of the high-temperature section of the lamination to ensure The curing effect of the prepreg. For example, insufficient curing of the prepreg will result in a large amount of glue removal relative to the prepreg of the core board, forming a stepped shape, and then the hole copper will be broken due to stress.
c. Difficulties in drilling
As the copper thickness increases, the thickness of the heavy copper PCB also increases. Heavy copper PCB usually has a thickness of more than 2.0mm. Due to the thicker board thickness and thicker copper thickness during drilling, it is more difficult to manufacture. In this regard, new tools are used to reduce the service life of the drill, and segmented drilling has become an effective solution for drilling heavy copper PCBs. In addition, the optimization of drilling-related parameters such as feed speed and retreat speed also have a greater impact on the quality of the hole.
The problem of milling target holes. When drilling, the energy of X-RAY gradually attenuates with the increase of copper thickness, and its penetrating ability will reach the upper limit. Therefore, for thicker copper PCBs, the first board cannot be confirmed when drilling. In this regard, you can set offset confirmation targets at different positions on the edge of the board, and mill out the offset confirmation target line on the copper foil according to the target position on the data when cutting the material. When lamination, the target hole and inner hole on the copper foil are milled out. The layer target hole corresponds to the production.
d. The problem of cracking of inner heavy copper pads (mainly for large holes above 2.5mm)
There is more and more need for heavy copper PCB, and the inner pads are getting smaller and smaller, and the problem of pad cracks often occurs during PCB drilling.
There is little room for improvement in this type of problem material. The traditional improvement method is to increase the pad, increase the peel strength of the material, and reduce the drilling speed of the drill.
Analyze the PCB processing design and technology, and propose an improvement plan: copper out processing (that is, when the inner layer of the pad is etched, the concentric circles smaller than the hole diameter are etched) to reduce the pulling force of the drilled copper.
The first drill will get a pilot hole smaller than the hole diameter of 1.0 mm and then performs normal drilling (that is, perform secondary drilling) to solve the problem of cracking of the inner heavy copper pad.
4. Application areas:
This heavy copper PCB is used in the field of industrial control. It is a MOS board for high-power supply control systems. Because of its very heavy copper thickness and the use of materials with CTI>600V, this heavy copper PCB can carry large currents, has good heat dissipation capabilities, and is resistant to voltage breakdown.
Traditional heavy copper boards are generally used in power control, military, and other fields. However, with the rapid promotion of new energy vehicles, the importance of heavy copper boards in the circuit board field is rising rapidly. It can be expected that the demand for heavy copper boards will increase in the near future. Will show explosive growth. But at the same time, the increasingly high requirements of customers have also brought great challenges to PCB manufacturers. We believe that with the advancement of material technology and the advancement of PCB manufacturers’ technology, many problems will be solved.