Drilling plays a crucial role in PCB design, facilitating electrical connections and component installation. Based on conductivity properties, holes can be classified into metallized and non-metallized holes, with metallized holes further divided into vias and component holes. These are the core structures for connecting interlayer circuits and supporting inserted components. During the prototyping phase, any slight oversight in the design of these two types of holes can lead to prototyping failures or subsequent soldering and performance issues. This article outlines the key points to avoid pitfalls with vias and component holes, based on the process capabilities of the leading domestic PCB prototyping manufacturer, Jialichuang.
A via, commonly known as a conductive hole, is used to connect different layer circuits and transmit current and signals. Its primary function is conductivity, without the need for insertion. This article will discuss vias using through holes as a default example for generality. A component hole, also known as a component hole, is used for installing components. During PCB manufacturing, to facilitate insertion, the hole diameter is compensated to ensure that the finished hole diameter is within the effective tolerance range. When designing PCBs with Jialichuang EDA, it is essential to properly set the drilling attributes and layer design.
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Drilling Attribute Settings
In Jialichuang EDA, the drilling diameter for double-sided boards ranges from 0.15 to 6.3 mm. For the vias and pads we commonly place, the “metallized” option in the drilling packaging attributes should be set to “yes.” Jialichuang uses a positive film process to manufacture PCBs, which involves copper plating the holes and then applying tin plating to protect the hole walls and required circuits, preventing the copper foil on the hole walls from being etched away during the etching process, thus achieving the manufacturing of metallized holes.
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Drilling Layer Design
In PCB design, pads with drilled holes must be placed on the required layers to achieve the through functionality of the PCB and the electrical connection of different conductive layers.
Next, let’s discuss the potential issues of mixing vias and component holes:
1) Abnormal filling and covering of vias
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Misusing vias in place of component holes: This can lead to vias being covered (filled) with oil or resin copper paste during PCB manufacturing, rendering them unusable for insertion and soldering.
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Misusing component holes in place of vias: The process for the hole in the center of a BGA pad can use resin/copper paste filling + cap plating, achieving an opaque and smooth effect. If misused, it will not be possible to achieve the filling (covering) of vias with oil or resin/copper paste.
2) Abnormal hole diameter
During PCB processing, metallized component holes undergo copper plating and spraying, resulting in a metal coating on the hole walls, which reduces the hole diameter. To ensure that the finished hole diameter meets design requirements, CAM engineers will make compensation adjustments in advance (e.g., increasing the compensation for double-sided tin-plated boards by 0.15 mm before drilling). Regarding hole diameter tolerances, Jialichuang’s process for component holes has a diameter of +0.13/-0.08 mm, ensuring that even if the diameter decreases during copper plating and spraying, the final diameter remains close to the design value, keeping the diameter within the effective tolerance range for smooth installation of component pins. The issue caused by misusing vias in place of component holes: vias are not used for insertion, and no diameter compensation is made before drilling, leading to a reduced diameter after plating. Even if not filled or covered with ink, the diameter may still be too small to allow for the installation of component pins.
The design of vias and component holes is fundamentally about matching processes with requirements. By leveraging Jialichuang’s publicly available process parameters and combining them with the electrical and structural needs of one’s own project, one can minimize the chances of rework during prototyping, allowing “small holes” to enhance PCB performance rather than hinder it.