Wiring Overview And Principles

With the rapid development of high-speed theory, PCB wiring can no longer be regarded as a simple interconnection carrier, but the influence of various distribution parameters must be analyzed from the transmission line theory. A distributed parameter circuit is a circuit in which the parameter distribution of the circuit elements must be considered. The distribution of parameters means that the potentials and currents of two adjacent points in the circuit at the same instant are not the same. This shows that the voltage and current in the distributed parameter circuit are not only functions of time, but also functions of spatial coordinates. At the same time, the complexity and density of PCBs are also increasing at the same time, from the design of copper-plated through holes, to the design of micro-holes, to the design of multi-level buried blind holes, and now there are buried resistance, buried capacitance, buried device design, etc. While high density brings great difficulties to pcb wiring, it also requires pcb design engineers to have a deeper understanding of the pcb production and processing process and its process parameters.

The wiring methods are divided into automatic wiring and manual wiring. At present, automatic wiring cannot meet the high standards of hardware engineers in many aspects, so it is generally realized by manual wiring.

DFM Requirements in Cabling

1. Hole

Mechanical drilling is generally recommended to be more than 8 mil, and the limit is 6 mil. Try to ensure that the thickness-diameter ratio is generally 10:1. The higher the thickness-diameter ratio, the more difficult it is to process. The width of the hole ring of the device is at least 8mil per side, and the width of the via ring is at least 4mil per side. The manufacturer will automatically optimize it during cam processing, and the solder mask opening is 50um per side.

The via pitch of the same net can be 6mil. The pitch of different network vias is 275um, and the pitch of different network devices is 425um.

The production is that the drill bit is generally 150um larger than the original hole, the drill bit is incremented by 0.05mm, and the larger drill bit will be incremented by 0.1mm. Then through holeization, electroplating meets the final finished product hole diameter requirements.

The distance between the non-metallized drilling and the edge of the board is 150um, that is, the hole will not be broken, and the conventional frame tolerance. Drill holes for metallization at least 10 mils to the edge of the board.

2. ETCH

0.5oz copper thickness, the thinnest line width can be 3mil, and the minimum spacing is 2mil.

1oz copper thickness, the thinnest line width is 3.5mil, and the minimum spacing is 4mil.

2oz copper thickness, the thinnest line width is 4mil, and the minimum spacing is 5.5mil.

The inner electrical layer should avoid copper by at least 20mil.

For small discrete devices, the traces on both sides should be symmetrical.

When the SMT pad pin needs to be connected, it should be connected from the outside of the solder pin, and it is not allowed to connect inside the solder pin.

For SMT pads, a flower pad connection is required when copper is applied to a large area.

ETCH lines are evenly distributed to prevent warping after machining.