As a measure to reduce the production cost of rigid multilayer printed circuit board, it can be started from various aspects such as the type, size, processing technology and materials of printed circuit board.
The influence of printed circuit board size design on cost.
The original size of the copper-coated plate is too large to be convenient for processing, and sometimes it can't even be put into the PCB processing equipment for processing. Therefore, it is necessary to cut it into pieces of copper-coated plates of machining size first.
As for the specific size of machining, it is necessary to determine the size of each printed circuit board according to the manufacturing equipment of printed circuit board, as well as some technological parameters.
These parameters in addition to outside need to the length and width of the printed circuit graphics itself, but also to frame fixed on the printed circuit board of electronic products that are consumed in the screw hole width, shape machining allowance, the technology of electroless plating, plating and corrosion of fixture clamping allowance, multilayer printed circuit board at the time of the dowel allowance, interlayer registration mark allowance, printed circuit board production manufacturer of marking allowance, printed circuit board edge width, etc., some process parameters recommended value to apply copper manufacturer or distributor.
During the production and processing of printing lines, according to the above data, it can be determined how many pieces of processing size of a large original size copper coated plate are cut, is it vertical cutting or horizontal cutting, can it be set cutting, etc.
The influence of layer number of printed circuit board on cost
The production cost of printed circuit board will increase sharply with the increase of the number of layers. Therefore, it is possible to make a large difference in cost due to the difference of one thought.
If you're having trouble designing a six-layer printed circuit board, don't give up speaking out of turn.
However, this is not an easy task, because when it comes to such things, designers may not hesitate to design an 8-layer printed circuit.
Iii. CEM-3 materials
Produce double-sided printed circuit board used double-sided coated copper, in addition to the widely used double-sided epoxy glass cloth coated copper, still have a kind of low cost CEM - 3 material, see figure 4.87. Its structure is the original double epoxy resin as base material in glass cloth coated copper thick epoxy glass cloth to make it very thin two chips, at this time due to insufficient strength, while in sandwiched between two thin slices of epoxy glass cloth of epoxy resin glass non-woven fabrics, which reduces the cost.
The CEM-3 material has a soft texture and can be used as the core material of multi-layer rigid printed circuit board besides being used independently.
The influence of line width and gap width on the cost of conductor graphics
If the width of the guide graph in the printed circuit board is represented by L, and the gap width between the conductor graphs is represented by S, then LIS represents the ratio between the width of the conductive band and the gap width.
As this ratio decreases, the production yield of printed circuit board will decrease sharply and the cost will increase.
This phenomenon is more obvious when the circuit density is high.
Therefore, we must not arbitrarily reduce the value of LIS.
The influence of hole diameter on cost
In the case of drilling bit into printed circuit board, when the hole diameter is lower than a certain value, the drilling depth of the drill will be shortened sharply.
That is to say, when drilling a hole with a small diameter, the drill needs to exit for heat dissipation many times, which will reduce the production efficiency and increase the cost.
Therefore, do not arbitrarily reduce the hole size;
The number of through-holes should also be minimized.
Fill the through-hole with silver paste
For the through-hole of double-sided printed circuit board, the connection between two circuits is realized without copper plating. Instead, the method of filling the through-hole with silver paste can also reduce the cost of double-sided printed circuit board.
The schematic diagram of the specific process is shown in figure 4.88.
This method is commonly used for two - sided copper coated ordinary phenolic resin board.
This method firstly cleans the surface of the normal phenolic resin board with copper on both sides, then prints the anti-corrosion graph on both sides with the screen printing method, forms the conductor figure after corrosion, removes the anti-corrosion layer and makes the hole through, then fills the hole with silver paste.
In order to make the silver paste in good contact with the conductor pattern on both sides, the silver paste should be bulging through the hole, and the diameter of the silver paste pattern in the part of the drum should be larger than the hole diameter.
In order to prevent the migration of silver ions, a covering layer is added on the surface of the silver pulp drum through screen printing.
Then, on both sides of the screen printing resistance welding graphics, isolation graphics, stamping or drilling out the fixed printed circuit board screw hole, processing appearance.
Finally, through the inspection, the silver paste filled through hole on the two - sided printed circuit board completed.
Silver paste filling through hole technology
Generally speaking, the double-sided printed circuit board with the silver paste filling the through-hole is not suitable for high reliability circuits due to the substrate.
In addition, there are a large number of non-conductive materials in the silver slurry besides the conductive materials, so the conductive properties of the silver slurry are not as good as that of the copper foil, which should be noted.