When designing high-speed circuits, designers need to predict the speed at which signals travel along lines on a printed circuit board (PCB). The signal must remain intact, but as handheld electronic devices become smaller and smaller, maintaining the PCB impedance within acceptable limits, engineers face increasing challenges.

 

In the mass production of high-frequency electronic products, it is necessary to use high-performance PCB impedance test equipment, which must be able to reliably verify whether the actual impedance value of the finished product has reached the calculated target impedance value.

 

Sam-Jeong Automation is a precision machinery manufacturer that uses Renishaw's TONiCTM incremental encoder and steel tape scale systems to ensure that its next-generation PCB impedance test equipment is sufficient for more demanding speed, accuracy and repeatability. Sexual requirements.

 

When producing printed circuit boards used in sophisticated high-frequency portable products such as smart phones, it is necessary to ensure that the impedance values of a single line and the entire circuit meet the specifications specified in the design phase, otherwise the signal integrity may be destroyed.

 

The resistance encountered when a DC signal is transmitted along a line on a PCB is usually defined as a resistance, and the measured value of the resistance encountered by an AC signal as it passes through a set of circuits including resistors, capacitors, and inductors is generally defined. For impedance, it is also referred to as "characteristic impedance." Impedance factors must be considered when designing high frequency signal boards. Therefore, accurate verification of PCB impedance is critical, and as products become more compact, this becomes even more important.

 

In the next five years, the size of smartphones may be smaller; the length and width may be shortened by 5mm and the thickness may be reduced by 1mm. Inside the phone, the multi-layer motherboard may have at least 12 layers. This increasingly accelerated miniaturization trend makes the control of impedance more challenging when designing PCBs.

 

The line width on the PCB is narrower, the distance between the lines on the horizontal and vertical planes is shorter, and it may be necessary to use a PCB substrate with a lower dielectric constant and a copper foil with a lower resistance (or a similar material). Foil). Regardless of the composition and structure of the material, the importance of ensuring the integrity of the signal transmitted on the PCB and verifying the true impedance level is only increasing.

 

In response to this challenge, Sam-Jeong Automation, a Korean supplier of precision motion control solutions, has developed automated PCB impedance testing equipment using its extensive electronic component manufacturing and testing expertise to meet the needs of large manufacturers in the consumer electronics arena. The stringent performance requirements.

 

Challenge

 

Positioning accuracy is a top concern for Sam-Jeong's developers when developing board impedance test equipment that can automatically detect such ultra-fine PCB structures. The measuring probe must be accurately placed on the densely distributed array of PCB test points.

 

Repeatability is also important, and test equipment must be able to compensate and adjust based on small deviations that occur during PCB production. It must also digest environmental conditions and thermal expansion effects in the production area.

 

Equipment speed is another key design indicator. In fast-paced, large-scale production environments, such as smartphone manufacturing facilities, Sam-Jeong's equipment needs to ensure that the PCB impedance testing process not only does not reduce but also maximizes productivity.

 

  solution

 

Sam-JeongAutomation's equipment features a classic gantry design that uses a high-speed linear motor driven impedance measuring probe in the X-axis and Y-axis directions to move along a pre-programmed path for precise positioning to the test point. The device is equipped with proprietary software to determine if the PCB impedance test results meet the specifications. The PCB to be tested is placed on the turntable in the center of the equipment workbench, and a high-resolution machine vision camera is used to identify the PCB test point location and complete the path programming.

 

Mr. YooHee-nok, deputy general manager of Sam-JeongAutomation, explained in detail the basic principle of impedance measurement: “Impact testing equipment, including our products, uses time domain reflection technology, which is TDR, and its principle is similar to radar. Pulse emission The device transmits a signal to the line under test through the probe. If there is any discontinuity or mismatch in the impedance during this process, part of the signal will be reflected back to the transmitter. Then, the TDR measures the voltage amplitude of the reflected signal and calculates the impedance change. As long as the time value from the reflection point to the emission point is measured, the software can determine the position of the mismatch impedance change point in the transmission path accordingly."

 

To ensure the positioning accuracy of the measuring probe, Sam-JeongAutomation selected the Renishaw TONiCTM incremental grating readhead with RTLC linear steel tape scale and FASTRACKTM rail system.

 

The TONiC series is an ultra-compact (35mm x 13.5mm x 10mm) non-contact incremental encoder designed for high dynamic precision motion control systems with advanced features, high precision, speed and reliability. It supports machines operating at speeds of up to 10 m/s. When used with an external Ti signal interface, the resolution is up to 1 nm with electronic subdivision.

 

To improve reliability and dirt and dust resistance, the TONiC readhead incorporates a third-generation optical filtering system that reduces noise and provides dynamic signal processing (including automatic gain control and automatic bias control). Ultra-low electronic subdivision error (±30nm) enables smoother speed control with improved scanning performance and positional stability.

 

 

PCB to be tested

 

On Sam-Jeong's equipment, the TONiC grating readhead is used in conjunction with a thin, compact RTLC stainless steel strip with a measurement of the total length of 500 mm along the X and Y axes. It is important to note that this scale is fixed in place with FASTRACK, a set of sturdy miniature rails. As Mr. Hee-nok explained: “The gantry of our equipment is made of aluminum, so thermal expansion must be prevented to adversely affect the accuracy of the grating system, so we use an RTLC scale with a FASTRACK rail. This problem is solved. The guide rail is used to fix the scale on the base. Since no adhesive or adhesive is needed, the scale can expand arbitrarily within the range of its own expansion coefficient. The principle is like the scale 'floating' On the substrate."