In PCB manufacturing, the precision requirements for pattern transfer are extremely high, which directly affects the performance and reliability of the circuit board. The following is an analysis of the key requirements and influencing factors for graphic transfer accuracy:
First, key precision requirements
Line width and line spacing accuracy
It is usually required that the line width tolerance be controlled within ±8μm (corresponding to 4/4mil lines) to meet the high-density wiring requirements.
The minimum line width and line spacing can reach 4mil (0.1016mm), making it suitable for high-frequency and high-speed signal transmission.
Interlayer alignment accuracy
The interlayer offset of the multi-layer board should be ≤75μm, and the precise alignment of the patterns of each layer should be ensured through processes such as four-quadrant targeting.
The offset of the hole position should be ≤50μm (0.2mm mechanical hole), and the accuracy of the drilling position is guaranteed through means such as X-Ray measurement.
External dimensions and hole position tolerances
The dimensional accuracy of the external shape can reach ±0.13mm, meeting the requirements of precise assembly.
The hole position tolerance is controlled within 0.05mm to ensure the high-precision installation of electronic components.
Second, factors influencing accuracy and control measures
Material properties and process compensation
The coefficient of thermal expansion (CTE) of the substrate directly affects dimensional stability. The influence of thermal stress needs to be reduced through pre-shrinkage treatment processes or dynamic CTE monitoring.
Asymmetric panel design may aggravate the uneven distribution of thermal stress. It is recommended to adopt a "mirror symmetrical" layout to balance the stress.
Equipment accuracy and calibration
The alignment accuracy of the exposure machine should be less than 25μm. High-end equipment is equipped with an automatic alignment system, which achieves sub-micron level adjustment through optical alignment marks.
Regularly calibrate the optical path system and mechanical motion system to ensure optical alignment accuracy and repeat positioning accuracy.
Environmental control
The production environment should maintain a cleanliness level of 100,000, with a temperature of 23±3℃ and a relative humidity of 55%±10% to prevent dimensional changes in the base material caused by environmental fluctuations.
The concentration of the developing solution is controlled at 0.8%-1.2%, the temperature is maintained at 30±2℃, and the error of the developing time does not exceed 10 seconds to ensure the consistency of the image transfer.
Process parameter optimization
The exposure energy is usually set within the range of 300-500mj/cm², and the parameters are adjusted according to the type of dry film.
During the drilling process, the accuracy of the hole diameter needs to be controlled. The allowable deviation for ordinary through holes is ±0.05mm, and for blind buried holes, it is ±0.03mm.
Third, precision verification and defect control
Intelligent detection and process monitoring
Deploy over 300 sensors to monitor 120 process parameters in real time, and integrate AOI+AXI+ICT to achieve a defect detection rate of 99.97%.
The graphic transfer online measurement system is adopted to automatically collect 200 positioning points per minute, and provide real-time feedback and adjust process parameters.
Quality traceability and improvement
Establish a traceability system to locate all process data of a specific production batch within 15 minutes through a QR code.
A four-level response mechanism is implemented to handle production anomalies. Minor anomalies are dealt with by the on-duty team leader, while major anomalies initiate a production suspension review.
