1. The impact of printed circuit board size design on cost
The original size of the copper-clad plate is too large, which is inconvenient to process, and sometimes it cannot be put into the printed circuit board processing equipment for processing. Therefore, it needs to be cut into several copper-clad plates of processing size first. As for the specific size of the processing size, it needs to be determined according to the processing equipment for making the printed circuit board, the size of each printed circuit board, and some process parameters. In addition to the length and width required by the printed circuit pattern itself, these process parameters also include the width consumed by the screw holes for fixing the printed circuit board on the electronic product frame, the process allowance for shape processing, electroless plating, electroplating and corrosion. The clamping allowance of the fixture, the positioning pin allowance of the multilayer printed circuit board, the alignment mark allowance between layers, the mark allowance of the printed circuit board manufacturer, the side width of the printed circuit board, etc., among which Some recommended values of process parameters can be obtained from copper clad laminate manufacturers or distributors. During the production and processing of printed circuits, the above data can be used to determine how many copper-clad sheets of processing size are cut from a large original-size copper-clad sheet, whether it is longitudinally or laterally cut, whether it can be cut or not, and so on.
Figure 4.86 is an example of cutting out a copper clad laminate to its original size. It is to cut a copper-clad plate of original size into 4 copper-clad plates of processing size, and each copper-clad plate of processing size contains 6 printed circuit boards. If the longitudinal dimension of the printed circuit board is increased by 1mm, then each copper-clad board of processing size can only be cut into 4 printed circuit boards, which will undoubtedly increase the cost of the printed circuit board to 6 printed circuit boards. 150% when the circuit board. It can be seen that according to the original size of the copper clad board, it is important to design the size of the printed circuit board reasonably.
Original size of copper clad plate
Original size of copper clad board and printed circuit board size
Second, the impact of the number of layers of printed circuit boards on the cost
With the increase in the number of layers of printed circuit boards, the production cost will increase sharply, so there may be a large difference in cost due to a single thought. If you encounter difficulties in designing a 6-layer printed circuit board, you must not give up lightly, perhaps a large amount of economic benefits is in your persistent efforts; however, it is not easy to reluctantly, because when the When encountering such a thing, in most cases, the designer may choose to design an 8-layer printed circuit without hesitation.
3. CEM-3 material
In addition to the widely used double-sided epoxy resin glass cloth copper-clad plate, there is also a low-cost CEM-3 material for the double-sided copper-clad laminate used in the production of double-sided printed circuit boards, see Figure 4.87. The thicker epoxy glass cloth used as the base material in the double-sided epoxy glass cloth copper-clad plate is changed into two very thin sheets. At this time, due to insufficient strength, the two thin epoxy glass cloths are placed between the two thin sheets of epoxy glass cloth. Sandwich epoxy glass non-woven fabric, thus reducing cost. The CEM-3 material is soft in texture and can be used as a core material for multi-layer rigid printed circuit boards in addition to being used alone.
Structure of CEM-3 material
Structure of CEM-3 material
4. The influence of the ratio of the line width to the gap width of the conductor pattern on the cost
If the width of the conductive pattern in the printed circuit board is represented by L, and the width of the gap between the conductive patterns is represented by S, then LIS represents the ratio of the width of the conductive strip to the width of the gap. As this ratio decreases, the production yield of printed circuit boards will decrease sharply, and the cost will also increase. This phenomenon is more obvious when the circuit density is relatively high. Therefore, the value of LIS must not be reduced arbitrarily.
5. The impact of the diameter of the through hole on the cost
In the case of drilling a printed circuit board with a drill, when the hole diameter is lower than a certain value, the drilling depth of the drill will be shortened sharply. That is to say, the same hole is punched. When drilling a hole with a small diameter, the drill needs to be withdrawn for heat dissipation many times, which will reduce the production efficiency and increase the cost. Therefore, do not arbitrarily reduce the diameter of the through holes; but also reduce the number of through holes as much as possible.
6. Fill the through hole with silver paste
For the through holes of double-sided printed circuit boards, instead of copper plating to achieve the connection of the two-sided circuits, the method of filling the through holes with silver paste can also reduce the cost of double-sided printed circuit boards. The schematic diagram of the specific process is shown in Figure 4.88. This method is generally used for common phenolic resin paperboard with double-sided copper coating. In the method, the surface of common phenolic resin paperboard coated with copper on both sides is first cleaned, and then a resist pattern is printed on both sides by screen printing. After etching, a conductor pattern is formed. The holes are filled with silver paste. In order for the silver paste to be in good contact with the conductor patterns on both sides, the silver paste should have a through hole, and the diameter of the silver paste pattern in the bulged part is larger than the diameter of the through hole. In order to block the migration of silver ions, a cover layer was applied by screen printing on the surface of the protruding part of the silver paste. Then, the solder mask pattern and the isolation pattern are screen printed on both sides, and the screw holes for fixing the printed circuit board are punched or drilled, and the shape is processed. Finally, through the inspection, the double-sided printed circuit board with the through holes filled with silver paste is completed.
Silver Paste Filled Via Process
Silver Paste Filled Via Process
Generally speaking, such double-sided printed wiring boards with through-holes filled with silver paste are not suitable for high-reliability circuits due to the base material. In addition, since there are a large number of non-conductive materials in the silver paste besides the conductive substances, the conductivity of the silver paste is not as good as that of the copper foil, and the readers should also pay attention.