Lay Stack up design guidelines

1. Inner board design requirement

• The edge of the inner board is filled with dummy pads.The pad diameter is required to be 4.0mm, and the spacing is required to be 1.5mm.
• The two layers of dummy pads corresponding to the inner layer board must be staggered by half the pad distance to balance the pressure during pressing.
• The dummy pads of adjacent rows should be staggered to improve flow resin.

In the PCB design, if the removed area by the rout is large, a dummy pad is required to be added to the rout area to increase the residual copper rate and reduce the filling. The pad diameter is required to be 4.0mm, and the spacing is required to be 1.5mm.

When designing in array, if the area removed by rout is relatively large, add a dummy pad in the routarea to increase the residual copper rate and reduce the filling. The pad diameter is required to be 1.5mm, and the spacing is 1.0mm.

• For designswith?broken edges, dummy pads must?be filled with a pad diameter of 1.5mm and a spacing of 1.0mm.
• lThe two layers of dummy pads corresponding to the inner layer board are required to be staggered by half the pad distance to balance the pressure during pressing

2. PP Design Requirements

1. The centrally symmetric structure can avoid the bending phenomenon caused by structural stress.

2.High R/C, thin fabric on the outer layer

• The same glass cloth combinationand high resin content are placed on the outer layer.
• Different kinds of glass cloth combinations, based on the principle of symmetry, thin fabrics are placed on the outer layer.

3.Warp to warp, weft to weft

The glass cloth yarn contains different yarn counts in warp and weft directions, resulting in different glue content and differences?in thermal expansion in the two directions.

4.Each layer of prepreg has a reasonable thickness

• The thickness andglue content is high. The thickness is not suitable for control
• Small thickness, low glue content,and low adhesion

5. Minimum number of layers

• Many layers, high cost, andnot suitable for process control

Pressing Method – Hydraulic Press

The structure of the hydraulic pressing machine is vacuum type and standard pressure type. The plate between the openings of each layer is clamped between the upper and lower hot plates. The pressure is from bottom to top, and the heat is transferred from both upper and lower hot plates to the plate.

Advantages: simple equipment,??low cost, large output.

Disadvantages: large amount of glue flow, poor thickness uniformity.

Thickness Control

Thickness test

• Use a thickness gauge to measure the thickness of the four corners and a midpoint of each plate
• The test point is 50 mm from the edge of the board
• Thickness tolerance: general thickness requirements ± 10%

Current thickness control after pressing

• Use a thickness gauge to measure the thickness of the four corners and a midpoint of each plate
• The?test point??is 50 mm from the edge of the board
• Thickness tolerance: general thickness requirements ± 10%

Multilayer PCB?is manufactured by stacking two or more circuits on top of each other, and they have reliable pre-set interconnections. Since drilling and plating have been completed before all layers are pressed together, this technique violates the traditional?manufacturing process?from the beginning. The two innermost layers are composed of traditional double panels, while the outer layers are different. They are composed of single independent panels. Before pressing, the inner substrate will be drilled, through-hole plated, pattern transferred, developed, and etched. The outer layer to be drilled is the signal layer, which is plated through so that a balanced copper ring is formed on the inner edge of the through-hole. The layers are then rolled together to form a multilayer PCB, which can be connected to each other (between components) using wave soldering.

Pressing may be done in a hydraulic press or an overpressure chamber (autoclave). In the hydraulic press, the prepared material (for pressure stacking) is placed under the cold or preheated pressure (high glass transition temperature material is placed at a temperature of 170-180°C). The glass transition temperature is the temperature at which an amorphous polymer (resin) or part of the amorphous region of a crystalline polymer changes from a hard and brittle state to a viscous, rubbery state.