1. Material selection
With the development of high-performance and multi-functional electronic components, high-frequency and high-speed signal transmission is brought. Therefore, it is required that the dielectric constant and dielectric loss of electronic circuit materials are relatively low, as well as low CTE, low water absorption and better high-performance copper clad materials to meet the processing and reliability requirements of high-rise boards. The commonly used sheet suppliers mainly include a series, B series, C series and D series. See Table 1 for the comparison of the main characteristics of the four inner baseplates. For the high-rise thick copper circuit board, the high resin content of the semi-cured sheet is selected. The flow of glue between the layers of the semi-cured sheet is enough to fill the inner layer of the figure. If the insulating medium layer is too thick, the finished board is likely to be too thick. If the insulating medium layer is too thin, it is easy to cause quality problems such as medium stratification, high-voltage test failure and so on. Therefore, the selection of the insulating medium material is very important.
2. Design of laminated structure
The main factors considered in the design of laminated structure are the heat resistance, voltage resistance, filling amount and thickness of medium layer, etc. the following main principles shall be followed.
(1) the manufacturer of semi curing sheet and core plate must be consistent. In order to ensure the reliability of PCB, single 1080 or 106 prepreg shall be avoided for all layers of prepreg (except for the special requirements of the customer). If the customer does not have the requirement of medium thickness, the medium thickness between layers must be guaranteed to be ≥ 0.09mm according to ipc-a-600g.
(2) when the customer requires high Tg plate, the core plate and semi-cured sheet shall be made of corresponding high Tg material.
(3) for the inner substrate 3oz or above, select the high resin content semi-cured sheet, such as 1080r / C65%, 1080hr / C68%, 106R / c73%, 106hr / C76%; however, try to avoid the structural design of all 106 high glue semi-cured sheets, so as to prevent multiple 106 semi-cured sheets from overlapping. Because the glass fiber yarn is too thin, the glass fiber yarn collapses in the large base material area, which affects the dimensional stability and explosive plate delamination.
(4) if there is no special requirement from the customer, the thickness tolerance of the interlayer medium layer is generally controlled by + / - 10%. For the impedance plate, the thickness tolerance of the medium is controlled by ipc-4101 C / m level tolerance. If the impedance influence factor is related to the thickness of the base material, the plate tolerance must also be controlled by ipc-4101 C / m level tolerance.
3. Interlayer alignment control
The accuracy of inner core board size compensation and production size control need to accurately compensate the figure size of each layer of high-rise board through the data and historical data experience collected in production for a certain period of time to ensure the consistency of the rise and fall of each layer of core board. Choose high-precision and reliable interlayer positioning mode before pressing, such as four slot positioning (pin Lam), hot-melt and rivet combination. The key to ensure the quality of the press is to set the proper pressing process and routine maintenance of the press. To control the press flow and cooling effect and reduce the interlayer dislocation. In order to control the alignment between layers, it is necessary to consider the compensation value of inner layer, the positioning mode of pressing, the technological parameters of pressing, the characteristics of materials and other factors.
4. Inner line process
Because the resolution ability of the traditional exposure machine is about 50 μ m, the laser direct imager (LDI) can be introduced into the production of high-rise board to improve the resolution ability of graphics, which is about 20 μ M. The alignment accuracy of traditional exposure machine is ± 25 μ m, and the alignment accuracy between layers is more than 50 μ M. By using high-precision alignment exposure machine, the alignment accuracy of graphics can be increased to about 15 μ m, and the alignment accuracy between layers can be controlled within 30 μ m, which reduces the alignment deviation of traditional equipment and improves the alignment accuracy between layers of high-rise boards.
In order to improve the etching ability of the line, it is necessary to give appropriate compensation to the width of the line and the pad (or pad) in the engineering design, as well as to make more detailed design consideration to the compensation amount of the special figure, such as the return circuit, independent circuit, etc. Confirm whether the design compensation of inner layer line width, line distance, isolation ring size, independent line and hole to line distance is reasonable, otherwise change the engineering design. If there are impedance and inductive reactance design requirements, pay attention to whether the design compensation of independent line and impedance line is sufficient, control the parameters during etching, and mass production can be conducted only after the first piece is confirmed to be qualified. In order to reduce the side etching, it is necessary to control the composition of each group of solution in the best range. The traditional etching line equipment is lack of etching ability, which can be technically modified or imported into high-precision etching line equipment to improve the uniformity of etching, reduce the problems of etching burr, etching unclean and so on.
5. Pressing process
At present, the interlayer positioning methods before pressing mainly include: four slot positioning (pin Lam), hot melting, rivets, combination of hot melting and rivets. Different product structures adopt different positioning methods. For the high-rise slab, adopt the four slot positioning method (pin Lam), or use the fusion + riveting method to make, and the ope punching machine punches out the positioning hole, and the punching accuracy is controlled within ± 25 μ M. In order to prevent subsequent delamination, X-ray should be used to check the lamination deviation of the first plate made by the bonding machine, and the batch can be made only when the lamination deviation is qualified. In batch production, it is necessary to check whether each plate is melted into the unit, so as to prevent subsequent delamination. The high-performance matching press is used for the bonding equipment, so as to meet the accuracy and reliability of interlayer alignment of high-rise plates.
According to the laminated structure of high-rise board and the materials used, the proper pressing procedure is studied, and the optimal heating rate and curve are set. In the conventional pressing procedure of multi-layer board, the heating rate of the pressed board is properly reduced, the high-temperature curing time is extended, the resin flows and solidifies fully, and the problems such as sliding plate and interlayer dislocation during the pressing process are avoided. The plates with different TG values shall not be the same as the grate plates; the plates with common parameters shall not be mixed with the plates with special parameters; to ensure the rationality of the given expansion and contraction coefficient, the performance of different plates and semi-cured sheets shall be different, and the corresponding plates shall be semi cured
Oct 21, 2019
