El problema de los orificios cercanos que no se pueden ignorar en el diseño de PCB multicapa

Publicado en 2020-02-18

When designing the PCB board, the most consideration for wiring is how to connect the various layers to the network signal lines. The denser the high-speed PCB board lines, the higher the density of vias (VIA), and the vias can play to each layer. The role of electrical connections. Multi-layer circuit board PCB proofing often receives feedback from the board factory that “holes are too close to the line, which exceeds the process capability.” So, if the vias are too close, will it be difficult to produce and will it affect product reliability?

1. Two holes too close will affect the aging of PCB drilling process. When the first hole is drilled after drilling the second hole, the material in one side is too thin, the drill bit is not uniformly stressed and the drill bit is not heat-dissipated, which will cause the drill bit to break, which will cause the PCB hole to collapse or be missed The hole is not conducting.

3. The hole position tolerance of the drilled hole is ≤0.05mm. When the tolerance is at the upper limit, the following conditions will occur in the multilayer board.

(1) When the lines are dense, small gaps appear irregularly through 360 ° to other elements. To ensure a safe distance of 3mil, the pads may have multi-directional PAD.

(2) Según los datos del archivo de origen, el borde del orificio al borde de la línea es de 6 mil, el anillo del orificio es de 4 mil y el anillo a la línea es de solo 2 mil. Para asegurarse de que haya una distancia de seguridad de 3 mil entre el anillo y la línea, se debe cortar el anillo de soldadura de 1 mil y la almohadilla después del corte es de solo 3 mil. . Cuando la compensación de la tolerancia de la posición del orificio es el límite superior de 0,05 mm (2 mil), al anillo del orificio le queda solo 1 mil.

4. La producción de PCB producirá una pequeña desviación en la misma dirección, la dirección de la almohadilla que se corta es irregular y, en el peor de los casos, se romperán los orificios individuales.

5. The influence of lamination deviation in multilayer boards. Taking a six-layer board as an example, two core boards + copper foil are laminated to form a six-layer board (Figure 5-1). During the pressing process, the core plate 1 and core plate 2 may have a deviation of ≤0.05mm when they are pressed, and the inner layer holes will also have irregular deviations of 360 ° after the pressing

To sum up, the drilling process affects the PCB yield and PCB production efficiency. There is no complete copper protection around the small hole of the ring, and the PCB open and short test can pass. There is no problem in the early use of the product, but the long-term reliability is not enough.

Multilayer PCB board, high speed PCB board hole-to-hole, hole-to-line spacing:

(1) Multilayer board inner hole to wire to copper:

4 layers: you can ignore

6 layers: ≥6mil

8 layers: ≥7mil

10 layers or more: ≥8mil

(2) Edge spacing of via diameter:

Same network via: ≥8mil (0.2mm)

Different network vias: ≥12mil (0.3mm