Tutorial For Solve Difficult Problems Related To PCB "Through-hole"

VIA, also known as metalized hole, is one of the important elements in PCB design. In the double side board and multilayer board, in order to connect the printed wire between the layers, a common hole is drilled at the intersection of the wires that need to be connected at each layer, that is, the hole. Blind Via, buried Via and throughVia are three types of perforations.

This article collected some and PCB “hole” related to the classic Q&A, I hope to help you.

It is often seen that there are many holes on PCB board. Are the more holes the better? Are there any rules?

A: No. Minimize the use of through-holes and, when they have to be used, consider reducing their impact on the circuit.

In the board wiring, if the line is dense, the hole may be more, of course, it will affect the electrical performance of the board, how to improve the electrical performance of the board?

Answer: for low-frequency signal, through the hole does not matter, high frequency signal as far as possible to reduce through the hole. If the line can consider multilayer board.

What is the difference between through-hole and blind hole in the signal? What are the principles that apply?

Answer: the use of blind holes or buried holes is an effective way to increase the density of multilayer board, reduce the number of layers and the size of the board, and greatly reduce the number of plated through holes. However, in comparison, through-hole in the process of better implementation, the cost is low, so the general design is used through-hole.

Can you explain the ratio between the downline width and the size of the matching hole?

A: It’s hard to say there’s a simple proportional relationship because the two simulations are different. One is plane transport and one is ring transport. You can find an online impedance calculation software through the hole, and then keep the hole impedance and transmission line impedance consistent.

What is the relationship between the width of the line and the size of the hole on the PCB board and the current through the size?

A: The copper foil thickness of a typical PCB is 1 ounce. If it is about 1.4mil, the maximum allowable current of about 1mil wire width is 1A. Through-hole is complicated, which is related to the size of the through pad and the thickness of copper deposited in the hole wall after electroplating during processing.

The hole should be matched according to the requirements of SQRT (L/C)?

A: yes, it is simply impedance matching, adjusting the parameters of the hole to achieve a better smooth impedance transition.

Is there a corresponding relationship between the temperature change and the impedance of the hole?

Answer: The temperature change mainly affects the reliability of the hole, and the CTE value of the material needs to be considered in the selection of materials.

High-speed PCB, how to deal with the hole avoidance in the wiring process, any good suggestions?

A: For high-speed PCB, it is better to drill fewer holes and to increase the signal layer to solve the need of adding more holes.

What is the function and principle of grounding in the vicinity of the wire through the hole?

Answer: PCB board through the hole, according to its function classification, can be divided into the following:

1) Signal through-hole (through-hole structure requirement has minimum influence on signal)

2) Power supply and ground through-hole (through-hole structure requires the minimum distribution inductance of through-hole)

3) heat dissipation through hole (through-hole structure requires the minimum thermal resistance of the hole)

The above mentioned through-hole belongs to the earthing type. The function of adding earthing through-hole near the routing through-hole is to provide the shortest backflow path for the signal.

Note: the signal pass-through layer is an impedance discontinuity point, from which the signal backflow path will be disconnected. In order to reduce the area surrounded by the signal backflow path, some ground passes must be made around the signal pass-through hole to provide the shortest signal backflow path and reduce the EMI radiation of the signal. This radiation increases significantly as the frequency of the signal increases.