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What’s the gang-mask shape around the pin field on a PCB? Why do we need it?
High-accuracy control is required during PCB assembly. In fact, the most crucial design consideration that makes all the difference in the long-term life and operation capability of a printed circuit board is the gang-mask contour surrounding the pin field area of a PCB.
And here’s an article that focuses on a detailed look into how the shape of the gang mask is a critical element in PCB design and thus impacts the entire process of assembly in the creation of high-quality electronic devices.
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What is a Gang-Mask Shape?
The “gang-mask” describes a concept whereby several pins fall under one masking design, or protection. It can also be defined as the pattern of solder mask surrounding several pins in a dense section of a PCB. At this point, the pin field, where multiple electrical contacts are made, it’s essential to apply a solder mask accurately so that by chance, there won’t be any contact between neighboring pins.
Isolating individual pins inside the gang-mask has made sure that only what needs to be soldered to gets exposed while at the same time avoiding other points in the board on which the solder is inadvertently dripping into.
Functions of a Gang Mask Shape on PCB
The shape above the pin field of a PCB that is formed by the gang-mask is very important and has various critical functions for use in the proper performance of electronic equipment.
These include the following:
Prevention of solder bridging:
- The main role of solder mask is preventing wetting between adjacent pins for closely packed pin fields, and gang-mask shape protects these pins from solder bridging, which might eventually cause electrical shorts.
Better soldering accuracy:
- Solder is applied only at required points, and gang-mask ensures this; the joints are therefore cleaner with greater reliability in solder.
The durability of PCBs is enhanced:
- Solder resist applied on gang-mask protects the PCB from moisture, dust, and chemicals existing in the environment. In this case, the PCB will last for a long period, especially when the circuit is exposed to extreme conditions.
Thermal protection while soldering:
- Solder mask protects the entire PCB against heat during wave soldering and reflow soldering processes. It also allows directing heat only on the solder joints without causing any kind of destruction to the rest of the components.
Benefits of the Use of a
Gang-Mask Shape Around the Pin Field
There are several advantages that make this gang-mask shape around the pin field on a PCB an indispensable feature in the assembly of PCBs. These include:
Precision in the application of solder:
- It clearly defines the boundaries for each pin in the pin field to ensure that only the necessary areas receive the solder. This is highly crucial in avoiding soldering errors in densely packed pin fields.
Prevents solder bridging:
- In high-density PCB designs where pins are placed very close to each other, if solder flows between adjacent pins, solder bridging will occur. The solder resist in the gang-mask prevents this by acting as a barrier that ensures each pin is electrically isolated.
Improved Reliability:
- In case the gang-mask shape is well implemented, the PCB can improve significantly on the reliability level due to preventing defectiveness in the form of short circuits or soldered joints.
Efficient Manufacturing:
- The gang-mask shape also makes it easier to manufacture because of the clear instructions for automated soldering machines to follow.
- Thus, less rework and higher yields in production during PCB assembly.
Types of Gang-Mask Shape on PCB
Common gang-mask shapes are mainly of circular and square shapes. Let’s understand the differences between various types of gang-mask shapes from the perspectives of advantages, principles, applications, and case study.
Circular Gang-Mask Shape
- Advantages:
In high-density multi-layer PCBs, space is a very precious resource, and it is very effective to utilize the limited space around a pin area with the adoption of a circular gang-mask shape.
- Principle:
Geometrically, a circle is without any sharp corner, which enables the functions of covering and protecting with a minimum waste of space around closely spaced pins. Such as the pin pitch is very small, gang masks in a round shape can form a continuous uniform protection area around the pins, which would lead to less short circuit risk between adjacent pins.
- Application:
In the process of signal transmission, a circle has geometric symmetry that reduces signal interference. The inner layer in high-density multi-layer boards has signal lines that are usually complicated and dense. A gang-mask in a circular shape can be used to supplement electromagnetic shielding methods. These methods reduce the impact of external electromagnetic interference on the pins, further improving the stability and accuracy of signal transmission.
- Case Study
For example, in some high-end smartphones, the gang-mask shape circularity is used in mass to achieve miniaturization and meet the requirements of high-performance. Based on the statistics of production data, after using this gang-mask shape, in the same PCB area, about 10-15 percent density can be increased while laying out the pins, and the rate of error for signal transmission can also be improved by 5-8 percent.
Square Gang-Mask Shape
- Advantages:
Flexible PCB manufacturing has its particularities. During bending and folding, for example, it needs to maintain structural stability and electrical performance. The square gang-mask shape is more compatible with the flexible PCBs manufacturing process.
- Principle:
The square is convenient to be precision positioning and aligning during the manufacturing process. In the square gang-mask on the production line of flexible PCBs, which can be more conveniently matched with other manufacturing processes (such as etching, drilling, etc.), when the flexible PCB is bent, the edges of the square gang-mask can better bear stress, so that problems such as cracking or peeling are less likely to occur, thereby protecting the pin area.
- Applications:
In terms of electrical connection, the square gang mask provides a more regular protection area for the flexible PCB pins, which is conductive to guaranteeing electric insulation performance in different bending states and avoiding a short-circuit between the pins.
- Case Study
This square gang-mask shape has been widely used in some wearable device’s flexible PCBs, such as smart watches. Based on the statistics of production data, after using the square gang-mask shape, the pin short-circuit failure rate after 1,000 bending tests of flexible PCB has been reduced from the original 1% to less than 0.1%, which greatly improved product reliability.
In addition to the above two very common shapes, there are also the following types of:
Shaped Gang-Mask Shape
- Shaped pads are those of irregular and non-standard forms. These pads usually are customized according to specific electronic components’ requirements or special soldering processes. For example, several special package forms of integrated circuits（ICs） require shaped pads due to pin arrangement and soldering needs.
Array in Gang-Mask Shape
- Array pads: more than one of the same or similar pads, according to some rules composed of pads. Array pads are usually used for a larger number of electronic components, such as: BGA package (Ball Grid Array), QFP package (four-sided pin flat package), etc.
Gang-Mask Shape Techniques
in PCB Assembly
Both PCB and circuit board assembly include applying solder mask and a design of gang-mask shape around the pin field. These are just some of the steps included in the processes:
Step 1: Design
Design is the initial step of the gang-mask shape process of a PCB. The engineers are so careful where they place components, what kind of copper trace routings are needed, and where the pin field must be placed so the board works the way it should.
Step 2: Application
After the PCB has been fabricated, the solder mask is applied on top of the copper traces; in the most important areas, such as the pin field, the gang-mask shape exposes only the necessary pins.
Step 3: Soldering
When soldering, the applied solder mask ensures that when it is attached onto the board, the component covers all exposed pins and prevents the bridging and defects.
Step 4: Quality Control
The PCB was inspected for assembly so that the solder mask and gang-mask applied were correct. All defects, including solder bridges and poor connections, would be detected and corrected before shipping the PCB.
Technology Discoveries
Research identified that the modified stencils are able to eliminate the problem of welding voids. Until now, the problem had been solved by changing the roughness of solder masks. In the preparation of samples using modified stencils, the effect of the solder mask on the void phenomenon is no longer important. The most important point is that modified stencils weaken the influence of solder masks effectively.[1]
Conclusion
The gang mask shape is a critical component in the PCB design, allowing designers to improve efficiency and accuracy. By preventing solder bridging and isolating the pins, designers can ensure that the system has optimal performance, durability, and improved thermal protection. The shape of a gang-mask element from the line of a simple consumer product to a complex aerospace system is showing long term endurance and efficiency in a PCB.
If you want to get more information on gang masks, Contact ELE using the contact page and get opinions from our experts.
FAQs
A gang mask (also known as a Solder Mask Pattern) is a pattern designed around multiple pins that prevent the solder from bridging. It ensures reliable connections across the whole PCB board.
Yes, the shape of the gang mask is an important factor because it isolates the pins and prevents them from getting shorted, leading to improved accuracy and PCB reliability.
With the development of material science, a research team has now developed a new type of mask material that can achieve that “The proposed approach by using low loss solder mask can improve the microstrip signal integrity more than 10%. [2]”
A variety of solder masks are used in the industry, offering features such as accuracy and reliability. Some of the common PCB masks are
- Epoxy liquid
- Liquid Photoimageable (LPI)
- Dry film solder masks
This section forms an important part of every PCB since it houses a number of electrical connections or junctions. It largely contains a huge number of pins or vias within a small area. Each pin is usually connected to different levels of the PCB or to link the PCB to external components. In areas with high-density PCB assembly, pin fields could be significantly congested, creating serious soldering problems. Proper gang mask shape surrounding the pin field prevents solder from spreading in between closely located pins, resulting in short circuits and low-quality connections.
References
- Kozak M, Vesely P, Dusek K (2023) Analysis of solder mask roughness and stencil shape influence on void formation in solder joints. In: Weld World, vol 67, pp 1347–1355. https://doi.org/10.1007/s40194-023-01505-7
- J. Hsu, T. Su, X. Ye and C. Lin, “Microstrip signal integrity enhancement by using low-loss solder mask,” 2017 12th International Microsystems, Packaging, Assembly and Circuits Technology Conference (IMPACT), Taipei, Taiwan, 2017, pp. 122 – 125, doi: 10.1109/IMPACT.2017.8255958.
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