Thick Copper PCB Fabrication
With the high development of Electricity, power, energy, electronic industry, the thick copper board is widely used by PCB design engineers. Thick copper PCB is mainly used for the central power system and power electronic devices, which is as it enables the board to conduct higher current and decrease the product size.
Normally thick copper board means the finished copper thickness of the board is more than 12 OZ, this is the most important factor for us to compare the thick copper PCB from that standard PCB with 1 OZ or 2OZ copper.
Thick Copper PCB
Thick Copper PCB Material
The base material used for a thick copper plate must have the following requirements.
1. High heat resistance resin system, high heat resistance.
2. Low expansion coefficient system.
3. Super high resin content and good porosity, so that it has a very excellent filling capability.
4. Special glass fiber structure, which can eliminate stress points and improve reliability.
Thick Copper PCB Layout Rules
PCB has a small volume, high density, many layers, complex layout, strong anti-interference ability, and high manufacturability.
A. Uniformity and Symmetry of Inner Layer Copper Laying
1. The layout of PAD Location
Due to the superposition effect of inner solder pads and the limitation of resin flow during lamination of thick copper, it is easy to make the high residual copper ratio of the place after lamination thicker than that of the place with low residual copper ratio, resulting in the thickness uniformity of the plate, affecting the subsequent placement and assembly
2. The thick Copper layout of the Inner Line Should Be Symmetrical
Due to the large thickness of copper, the difference between the CTE of copper and the CTE of the base material is large, and the change of thickness under pressure and heating is quite large.
The problem of warpage is easy to occur due to the asymmetric distribution of inner copper.
3. Laying Copper Spots or Blocks on No Copper Area of Inner Layer
The large copper surface can be changed to copper point to optimize the layout of wiring, with uniform density and good consistency, so as to reduce the structural consistency after pressure and heating.
B. Increase Residual Copper Rate of Inner Layer for Thick Copper
When the copper thickness is increased, the line gap is deepened, and the residual copper rate is the same, the resin filling is increased, and the semi curing sheet is increased.
If the resin is too small, it is easy to lead to the lack of glue layering and uneven plate thickness.
If the residual copper rate is low, it needs much resin filling, and the resin flow is limited.
Under the action of pressure, the thickness of the dielectric layer in the copper area, the line area, and the base material area is different. The thickness of the dielectric layer between the lines is the thinnest, which is easy to cause the failure of Hi-Pot.
C. Increases Width and Spacing of Line for Thick Copper
1. Thick copper plate, increasing line width and line spacing helps to reduce the difficulty of etching.
2. It can improve the effect of laminating and filling glue, with large spacing and more glass fiber cloth filling, and large spacing can reduce the filling pressure of glue.
D. Inner PAD Layout Optimization of Thick Copper
1. The thickness of copper is large, Multi-layer stacking, and copper stacking is larger. The drilling tool is easy to wear due to long-time friction, which affects the quality of the hole wall and the reliability of the hole. It is suggested that the layout of the inner layer non-functional pad should be as few as possible, no more than four layers.
2. The pad should be designed as large as possible. The small pad will produce more stress in the drilling process, and the heat conduction speed will be fast in the process of treatment, which will easily lead to the copper corner crack of the pad.
3. Add Inner Layer Independent PAD to Hole Wall.
Increase the effective distance between the hole copper and the inner welding pad, reduce the micro-short and caf failure caused by the hole wall quality.