Multilayer PCB circuit boards often encounter "holes to the line too close, beyond the capacity of the process" problem, we design the PCB board, the most considered is how the wiring can be connected to each layer with the most reasonable network signal lines. The more dense high-speed PCB lines over the hole (VIA) placed on the greater the density, over the hole can play a role in the electrical connection between the layers.
Close to the hole on the production of what difficulties will cause? And we need to pay attention to what near-hole problems? We will tell you one by one.
1. drilling operation if the two holes are too close to the PCB drilling process will affect the timeliness. As a result of drilling the first hole after the second hole in the drilling direction of the material will be too thin, resulting in uneven force on the drill nozzle and drill nozzle heat dissipation, resulting in broken drill nozzle, resulting in PCB hole collapse unsightly or leaky drilling not conductive.
2. PCB multilayer board over the hole will be in each layer of the line have hole ring, and each layer of the hole ring around the environment is different, there are also not pinched line. PCB board factory CAM engineers in the optimization of the file, there will be pinched line too close or hole and hole too close to the hole ring cut off part of the case, to ensure that the welding ring to different networks copper / line has a safe distance of 3mil.
3. Drilling hole tolerance is ≤ 0.05mm, when the tolerance on the limit of the multilayer board will appear the following situations.
(1) when the line is dense over the hole to other elements 360 ° irregular appearance of small gaps, to ensure a safe spacing of 3mil, the pad may appear multi-directional chipping.
(2) according to the source data calculation, hole edge to the edge of the line 6mil, hole ring 4mil, ring to the line only 2mil, to ensure that the ring to the line between the safety of 3mil spacing is required to cut 1mil solder ring, after cutting the pad only 3mil. when the hole tolerance offset if the upper limit of 0.05mm (2mil), the hole ring only 1mil.
4. PCB production will appear in the same direction of a small amount of offset, the direction of the pad is cut irregularly, the worst phenomenon will also cause individual holes broken solder ring.
5. PCB multilayer board within the impact of the press fit deviation. Six-layer board, for example, two core board + copper foil pressed together to form a six-layer board. Pressing process, core board 1, core board 2 pressed together may have ≤ 0.05mm deviation, pressed together after the inner layer of the hole will also appear 360 ° irregular deviation.
From the above problems concluded that the PCB punching yield and PCB board production efficiency is affected by the drilling process. If the hole ring is too small and no complete copper protection around the hole, although the PCB can pass the open short circuit test and the use of pre-products will not have any problems, but the long-term use of reliability is not enough.
Therefore, multi-layer PCB board, high-speed PCB board hole to hole, hole to line spacing recommendations.
(1) multilayer board inner layer hole to line to copper.
4 layers: do not care
6 layers: ≥ 6mil
8 layers: ≥ 7mil
10 layers or more than 10 layers: ≥ 8mil
(2) over the hole inside diameter edge spacing.
With the network perforation: ≥ 8mil (0.2mm)
Different network perforation: ≥12mil (0.3mm)