Perfecting Inspection Operations

A major supply chain solutions company performs printed circuit board (PCB) assembly. The solder connections on the PCB are inspected with a Vitrox vision solder inspection machine. A 2D Data Matrix code on the bottom of each PCB needs to be read at the time of inspection so the inspection results can be stored in a database.

Originally the customer was not able to read the Matrix codes because its Advanced Optical Inspection (AOI) system wasn’t equipped with a camera on the bottom. Interlatin, a manufacturing solutions integrator, solved the problem by installing a vision-based reader that handles a wide range of degradations to the printed code. The result was a read rate over 99.9% and a significant improvement in the throughput of the assembly process.

2D Data Matrix Code Reading Challenges

The supply chain solutions company produces a wide range of PCBs for its customers and often inspects solder connections with ViTrox AOI systems that offer inspection speeds up to 55 cm2/sec for post-reflow and 65cm2/sec for pre-reflow.

“Our responsibility was to provide the AOI system and make it work in this application,” said Alejandro Lara, Inside Sales Manager for Interlatin. “But we were concerned that the code reader that is most commonly used in this type of application would be unable to provide high enough read rates due to degradation seen in the codes. Though Data Matrix codes have built-in error correction, “no-reads” can still occur when codes are incomplete. So we needed fast, compact reader capable of reading codes with varying amounts of degradation. Another requirement was the ability to emulate a USB keyboard in order to easily interface with the Vitrox AOI system.”

PCBs can be marked with several different marking technologies, such as dot peen or laser etching. 2D Data Matrix Codes require as little as 20% contrast between the code and the marking surface, much less than linear barcodes. This allows the code to be marked on difficult surfaces of metal, non-metallic, and plastic components. Built-in error correction allows the encoded information to be captured even if the Data Matrix symbol is somewhat degraded. But the range of 2D Data Matrix marking techniques and PCB materials means that the appearance of the marks can vary dramatically from one situation to the next.

The result is often codes with low contrast, poor cell position, or inconsistent cell size. In addition, the surface being marked can be matted, cast, or highly reflective, and is seldom as clean and uniform as a white label. In addition to the selected marking method, the parts come in different colors or shapes and can be made from different materials. Surfaces include smooth and shiny, furrowed, striped, streaked, or coarse granular. Reading such marks has been an enormous challenge until recently.

Space and Time Limitations

In this application, a conveyor feeds PCBs into the machine, but code reading needs to be performed outside the machine because of the potential for the machine to be moved. Only about two inches are available above the surface of the PCB to mount the reader. The high speed and continuous operation of the conveyor gives the reader little time to acquire and analyze the image.

The Cognex DataMan 100 code reader met all the requirements of this application. This image-based reader uses solid-state camera technology to capture full-frame images in a single snapshot, avoiding the need to cross a barcode with scan lines from end to end the way lasers do. When an imager captures a frame containing a barcode, it can locate that code anywhere within the frame.

Thus, in effect, each image contains thousands of scan lines in all directions, making the ability to find and read barcodes more efficient. Image analysis software algorithms can interpret a higher percentage of the captured codes than laser scanners can, and they can also manage the complexities of 2-D codes. In addition, the images themselves can be stored for training, historical analysis, or documentation.

Algorithm Provides High Read Rates

The DataMan 100 code reader incorporates the 2DMax+ algorithm for continuously high read rates for high speed identification applications. With the algorithm, the reader can identify and decode even severely damaged or poorly marked 2-D Data Matrix codes. The reader is unaffected by variations in lighting, marking method, code quality or surface finish.

Because these two-dimensional codes, like the Data Matrix, can hold a much larger volume of data, they provide a considerable amount of redundancy that is used for error correction. 2DMax+ can read Data Matrix codes even when critical elements are missing. 2DMax+ can also locate and decode Data Matrix codes that are overexposed or underexposed, without requiring multiple retries. This improves throughput, speed and overall reliability.

DataMan 100 image-based barcode readers provide up to 45 reads per second, ease-of-use, lighting, camera, processor, and communications into an exceptionally small, industrial-rated housing measuring just 23 x 42 x 64 mm. When connected to a PC over USB, the DataMan 100 appears as either a COM port or a standard USB keyboard. The user can control the connection type by scanning the desired connection code.

Improved Throughput on Inspection Operation

From the moment the image based ID reader started operating, it produced a near 100% read rate.

“Our customer was very pleased to have such high read rates,” said Dacil Amelia Cruz, Marketing Specialist for Interlatin. Since the new image-based reader was put in place, the supply chain solutions company has increased production by reducing downtime required for opening the inspection machine and manually entering the labels. Management is so pleased with the ID reader that it is planning to purchase additional devices for other packaging lines.

“We have seen consistently better results with Cognex ID readers on difficult 2D Data Matrix applications,” Lara concluded. “As a result, we have been moving other customers over to this same solution and we have had consistently good results. The result is substantial time savings and throughput improvements for our customers. Our company also saves time because the new readers reduce the amount of time that we have to spend adjusting ID readers. The new image-based ID readers are also economical to purchase and easy to maintain.”

About Cognex

Cognex Corporation is an American manufacturer of machine vision systems, software and sensors used in automated manufacturing to inspect and identify parts, detect defects, verify product assembly, and guide assembly robots. Cognex is headquartered in Natick, Massachusetts, USA. It has offices in more than 20 countries.