Reasons for PCB Manufacturing File Engineering Compensation

In the design and manufacturing process of PCBs (Printed Circuit Boards), various factors such as material properties, manufacturing processes, and environmental conditions can significantly influence the electrical characteristics and overall performance of the PCB. To ensure the final product meets the required standards, it is essential to implement appropriate compensation measures. This article delves into the necessity of production compensation in PCB manufacturing, focusing on critical areas such as trace width, drilling, pad design, material properties, and electrical characteristics.

Understanding the Fundamentals of PCB Production Compensation

PCB production compensation refers to the strategic adjustments made during the design and manufacturing processes to counteract the inevitable variations and tolerances inherent in PCB fabrication. These compensations ensure that the final PCB product meets the intended electrical, mechanical, and performance specifications despite the physical changes that occur during production.

As PCB designs become more complex, with higher component densities, finer traces, and stricter performance requirements, the margin for error in production becomes increasingly narrow. Production compensation serves as a crucial bridge between the ideal design specifications and the physical realities of manufacturing processes.

Trace Compensation

1. The Reason for Trace Width Compensation

During PCB fabrication, traces undergo several processes that can alter their dimensions, notably etching. Etching removes copper to create the desired circuit pattern, but it is not a perfectly vertical process, leading to “side etching” or “undercut.” Side etching occurs when the etchant solution removes copper from the sides of the trace as well as the top, resulting in narrower traces than designed. This can compromise the trace’s current-carrying capacity and signal integrity.

2. Calculating Trace Width Compensation

To counteract side etching, PCB designers must apply trace width compensation, which depends on several factors such as copper thickness, etching process, board material, and trace width and spacing. A general rule of thumb is:

Compensation = 1.5 * Copper Thickness

For instance, for 1 oz copper (1.4 mils or 35 μm thick), the compensation would be 1.5 * 1.4 mils = 2.1 mils (approximately 53 μm). Thus, traces should be designed 2.1 mils wider on each side than the final desired width.

This is a conventional circuit board compensation method. When the factory compensation value is uncertain, it is advisable to increase the line width and line spacing if possible. If the board contains many densely packed lines that cannot be optimized for line width and spacing, our company can still produce it. We utilize a dynamic compensation method to control the line width and spacing on the board.

However, if there are only a few small spacings, it is recommended that the designer optimize the solution, as the cost will increase, particularly for high-level PCBs. If it is not an impedance line, you can directly instruct the CAM engineer to optimize the spacing to meet conventional production capabilities. Therefore, it is crucial to consider the cost factor while adhering to the best practices of PCB design.

3. Advanced Trace Compensation Techniques

Advanced PCB designers use sophisticated techniques for compensation:

a. Differential Pair Compensation

For high-speed differential pairs, maintaining consistent impedance is crucial. Compensation must be applied not only to the trace widths but also to the spacing between the traces. This often requires iterative simulation and testing to achieve optimal results.

b. Length Matching Compensation

In high-speed designs, trace length matching is essential for maintaining signal timing. Compensation must account for changes in trace length due to etching, ensuring matched traces remain within the required length tolerance after manufacturing.

c. Impedance-Controlled Trace Compensation

For impedance-controlled traces, width compensation must be carefully calculated to maintain the desired impedance after etching. This often involves collaborating closely with the PCB manufacturer to determine the exact stack-up and material properties used in production.

Drill Compensation

1. The Reason for Drill Compensation

The hole sizes specified in Gerber files typically refer to the finished dimensions after all manufacturing processes, including copper plating and surface treatments. These processes can reduce the hole size, requiring compensation to ensure the final dimensions meet specifications.

2. Industry Standards for Drill Compensation

The drilling compensation value is derived from production capability testing. For instance, if the final hole size required is 1.00mm and the plating adds thickness, the engineering department might use a 1.15mm drill bit. This ensures that the final hole size after plating meets the design specifications. Drilling compensation is related to the surface process and the size of the drill hole. Typically, for processes like tin spraying, a compensation of 0.15mm is used, while for gold immersion, a compensation of 0.1mm is applied. This explains why CAM engineers frequently confirm issues like insufficient hole spacing and small hole spacing. Understanding these issues allows for effective avoidance, enabling CAM engineers to quickly and efficiently optimize Gerber files.

It is especially important to pay attention to the choice of via sizes. If PCB designers consider via compensation in advance and enlarge the corresponding drill pads accordingly, the designed PCB files will gain a good reputation among CAM engineers. This proactive approach ensures that the drill pads remain adequate after compensation, facilitating smoother and more efficient file optimization.

Pad Compensation

Importance of Pad Compensation

Pad compensation is crucial for ensuring reliable connections and high-quality soldering. The manufacturing process can alter pad size and shape due to factors such as temperature and pressure. Without proper compensation, these changes may result in poor soldering quality, loose connections, or soldering failures.

Pad Compensation Methods

a. Diameter Compensation: Adjust the pad diameter to match component specifications, typically within a 10% tolerance.

b. Shape Compensation: For SMDs on large copper surfaces, pad size is determined by the solder mask opening size. To maintain the original SMD size, the solder mask opening on the large copper foil is selected separately. The original CAD SMD size plus the compensation value is used to ensure that the SMD on the large copper surface matches the SMD on the trace.

c. Spacing Compensation: Ensure sufficient spacing between pads to prevent short circuits. The recommended minimum spacing for BGA and IC components is 0.15 mm. When the via hole diameter is too large and the pad is too small, CAM engineers will expand the pad overall or shave it to maintain the solder ring while ensuring proper spacing.

Material Compensation

Material compensation is essential for ensuring the stability and reliability of PCBs during and after production. Different PCB materials have varying thermal expansion coefficients, which affect the board’s dimensions during production. Without proper compensation based on these coefficients, the board may experience warping, cracking, or other forms of deformation that compromise its functionality. To maintain stability, it is crucial to accurately calculate and apply the necessary adjustments to account for these thermal expansion differences.

Additionally, the dimensions and materials of the printed circuit diagram significantly influence the PCB’s final size and shape. During production, appropriate adjustments must be made to ensure consistency with the design specifications. This involves careful control of manufacturing process parameters, including temperature, humidity, and heating time, which must be precisely regulated to accommodate the specific requirements of different PCB types. By making these adjustments, manufacturers can achieve the desired stability and performance in the final product.

Conclusion

Compensation in PCB production addresses factors that can impact the board’s performance and reliability. By implementing trace width, drilling, pad design, material, and electrical characteristic compensation, manufacturers like Highleap Electronic can ensure their PCBs meet stringent quality standards and perform reliably in their intended applications.

At Highleap Electronic, we are committed to addressing these factors meticulously, resulting in superior performance, reduced failure rates, and higher customer satisfaction. Trust Highleap Electronic for your PCB needs, and experience the difference that precision and dedication can make.