Effective measures to reduce the cost of printed circuit production

- Aug 18, 2018-

As a measure to reduce the production cost of rigid multi-layer printed circuit board, we can start from the type, size, processing technology and materials of printed circuit board.

As a measure to reduce the production cost of rigid multi-layer printed circuit board, we can start from the type, size, processing technology and materials of printed circuit board. 

1. Impact of printed circuit board size design on cost

The original size of the copper plate is too large, so it is inconvenient to be processed. Sometimes, it cannot even be processed in the printed circuit board processing equipment, so it needs to be cut into several pieces of processed size copper plate first.The specific size of the printed circuit board shall be determined according to the processing equipment, the size of each printed circuit board and some process 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 the printed circuit, it can be determined according to the above data how many pieces of processed size are cut into a large original size copper plate, whether it is cut lengthwise or crosswise, and whether it can be cut or not. 

FIG. 4.86 is an example of cutting a copper sheet in original size.It is to cut a piece of original size copper plate into 4 processing size copper plate, and each processing size of copper plate contains 6 printed circuit boards.If the longitudinal size of the printed circuit board is increased by 1mm, then each prefabricated copper plate can only be cut into 4 printed circuit boards, which will undoubtedly increase the cost of printed circuit boards to 150% of the cost of 6 printed circuit boards.Thus it can be seen that the importance of reasonable design of printed circuit board size according to the original size of copper clad board. 

Original size of copper clad plate

Copper plate original size and printed circuit board size

2. Impact of the number of layers on the cost of printed circuit board

As the number of layers increases, the production cost of the printed circuit board will increase sharply, so it is possible to make a big difference in cost due to one miss.If you're having trouble designing a six-layer printed circuit board, don't give up on speaking out of turn.However, this is not easy to resist, because when such things happen, in most cases the designer may not hesitate to choose to design an 8-layer printed circuit. 

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 material of CEM-3 is soft. In addition to being used alone, it can also be used as the core material of multi-layer rigid printed circuit board. 

The structure of CEM-3 materials

The structure of CEM-3 materials

The relative cost of line width and gap width of conductor figure

If L is used to represent the width of the leading figure in printed circuit board and S is used to represent the gap width between the conductor figure, then LIS represents the ratio of the width of the conductive band to the gap width.As this ratio decreases, the production yield of printed circuit board decreases sharply and the cost increases.This phenomenon is more obvious when the circuit density is higher.Therefore, we cannot arbitrarily reduce the value of LIS. 

The aperture of the through-hole influences the cost

In the case that the drill is used to drill holes on the printed circuit board, when the hole size is lower than a certain value, the drill depth will be shortened sharply.That is to say, when drilling a hole with a small hole, the drill has to withdraw heat several times, thus reducing production efficiency and increasing cost.Therefore, do not reduce the hole size at will;The number of through-holes should also be reduced as much as possible. 

Fill the hole with silver paste

For the through-hole of double-sided printed circuit board, the connection of two-sided circuit is realized without copper plating, but the method of filling the through-hole with silver paste can also reduce the cost of double-sided printed circuit board.The detailed process is shown in FIG. 4.88.This method is commonly used in common phenolic resin board with copper on both sides.The method firstly cleans the surface of the common phenolic resin board with copper on both sides, and then prints the corrosion resistant pattern on both sides with screen printing. After the corrosion, the conductor figure is formed. After removing the corrosion resistant layer, the hole is drilled through, and then the silver paste is filled into the hole.In order for the silver paste to be in good contact with the conductor figure on both sides, the silver paste should be pumped out of the through hole, and the diameter of the silver paste figure in the extruded part is larger than that of the through hole.In order to prevent the migration of silver ions, a covering layer is applied to the surface of the extruded part of the silver paste through screen printing.Then, on both sides of screen printing resistance welding graphics, isolation graphics, stamping or drilling fixed printed circuit board screw holes, processing shape.At last, the double-sided printed circuit board with silver paste filling through hole was finished. 

Silver paste filling through hole process

Silver paste filling through hole process

Generally speaking, the double-sided printed circuit board with the silver paste filling through the hole is not suitable for high reliability circuit due to the base material.In addition, there are a large number of non-conductive materials in the silver paste besides conductive materials, so the conductive performance of the silver paste is not as good as that of copper foil, which should also be brought to the attention of readers.