PCB solder mask ink according to curing method , solder mask ink has photosensitive developing ink , there are heat-curing thermosetting inks, There are also UV light-cured UV inks. , and PCB hard board solder mask ink, FPC soft board solder mask Ink , and aluminum substrate solder mask ink , aluminum substrate ink can also be used on ceramic boards.
Vias are generally divided into three categories: blind vias, buried vias, and through holes. “Blind vias” are located on the top and bottom surfaces of printed circuit boards. It has a certain depth and is used to connect the surface circuit and the inner circuit. , Circuit The “through hole” passes through the entire circuit board. , from the top layer to the inner layer and then to the bottom layer.
Vias in PCB solder mask processing , Common via processes include: via cover oil, via plug oil, via window opening, Resin plugging, electroplating filling, etc. , each of the five processes has its own characteristics , each has its own function and corresponding application scenario.
Five via processing methods and application scenarios
1. Via cover oil
Via cover oil refers to the process of covering the via pad with ink, without tin on the pad. Most circuit boards use this process. The designed aperture is not recommended to be larger than 0.5mm. If the aperture is too large, the ink will accumulate in the hole, which may cause quality problems. When converting the design file to a Gerber photolithography file, the via opening needs to be cancelled, otherwise the via will be opened instead of covered with paint. .
2. Via window
Via window means that the via pad is not covered with oil and copper is exposed. After surface treatment, it is immersion gold or tin spraying. The function of via opening is When the component is wave soldered, spraying tin onto the inner wall of the hole will increase the current conduction capacity of the hole. Same , there is no need to cancel the via opening when converting the Gerber file.
3. Oil plugging of vias
Via plugging oil refers to plugging the via hole wall with ink During production, use aluminum sheet to fill solder mask ink into the via hole . ,Again The purpose of the via plugging oil is to prevent the tin from penetrating the component surface from the via hole during wave soldering and causing a short circuit. When converting the design file to Gerber, the via opening should also be cancelled.
4. Resin plugging
Resin plug hole means that the via hole wall is filled with resin, and then the pad is plated flat. It is suitable for any type of via with a window on one side. The purpose of resin plugging holes is, from a process perspective, for example, blind buried holes are drilled before pressing. If the hole is not plugged with resin, the pressed PP glue will flow into the hole. , resulting in lamination glue shortage and board explosion. It is said that there are vias drilled on the pad If the hole is not filled with resin and electroplating , small welding area will lead to poor welding.
5. Copper paste filling
Copper paste filling means filling the via hole wall with copper paste and then flattening the pad. It is suitable for any type of via with a window on one side. The purpose of copper paste plugging is to apply to the over-large current of the via in the disk. The cost of copper paste plugging is much higher than that of resin plugging. If the via opening is cancelled in the design file, the via opening can be cancelled .
Solder mask file design for vias
1. Altium via cover oil and window opening
Setting via opening or oil covering in Altium software As shown in the figure: The arrow mark is the oil cap , uncheck Open the window. To set a single via, double-click the via and check the two options as shown in the picture . Remove the oil cover without opening the window, You can use Find Similar to select all vias. Then execute F11 You can open the PCB inspector Then check the box as shown in the picture.
2. PADS via cover oil and window opening
Set via opening or capping in PADS software , as shown in the figure : Click the solder mask file when converting the Gerber file ,bomb Click “Layer ” in the window and check the via option to open the window. , if you don’t hook the hole, it means you are covering the oil.
3. Allegro via cover oil and window opening
Set via opening or oil covering in Allegro software , as shown in the figure: Convert to Gerber File , add VIA CLASS to the solder mask layer , open the via window , add TOP to the top layer and BOTTOM to the bottom layer . The file has a hole opening , without adding VIA CLASS , the oil is covered.
In conclusion, proper via processing and solder mask file design play a critical role in ensuring PCB functionality, quality, and reliability. Selecting the appropriate via processing method—be it via cover oil, via window, oil plugging, resin plugging, or copper paste filling—depends on the specific application and requirements of the PCB. Additionally, accurately setting up the solder mask file in design software such as Altium, PADS, or Allegro is essential to avoid manufacturing issues and achieve optimal performance. By understanding and applying these techniques, PCB designers and manufacturers can ensure robust and reliable circuit board production.
