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Publication Date: 03/1/2010
Archive >  March 2010 Issue >  Special Features: SMT and Production > 

Flying Prober Automates Production Testing
SPEA 4040 Multimode flying prober set up for fully automatic mode at the Datasensor plant.

Flying probe testers have become central to today's medium-to-high-production volumes — mainly because of the flying prober's improved productivity, their flexibility in operation, and the capability of easily testing the most complex and miniaturized PC boards.

One company that has learned the importance of the flying prober is Datasensor — a part of Datalogic Group — a company that develops, manufactures and commercializes photoelectric devices for detection, safety, measurement and inspection in industrial automation. Datasensor's quality policy aims squarely at eliminating defects at the end of the SMT process, and this all hinges on the flying probe test.

Datasensor's success is based on the ability to anticipate ever-changing market expectations, through the flexible management of a highly automated production process.

"Our strength has always been continuous innovation" explains Mirko Tomaselli, Facility and Process Engineering Manager. "In order to follow market demands, we are always researching technological solutions for mounting components that are becoming extremely tiny both in dimensions and circuit density. To be competitive, without moving the production abroad, we have zeroed in on automation and productivity, basing the process on equipment that represents the state-of-the-art in the production technology."

In this context, electronics production testing has to meet these same requirements — to be both highly flexible and highly automated — allowing the company to implement a product quality and testing policy that totally eliminates defects from the finished product that goes out the door.

Test Flexibility
In order to attain the best results both in reducing the cost of test cost improving product reliability, Datasensor has embraced the flexibility and productivity of the latest-generation of flying probe systems. Today's flying probers have replaced the bed-of-nails stations at the end of the SMT process, which today represent old, outmoded technology. Yes, they can be made to work well, but at a high price in time and cash outlay for fixturing — perhaps justifiable for massively large production runs.

In fact, the flexible management of the production line is an essential element for this company, whose high-mix production has to face global market requests every day. "We may have to change seven or eight setups a day, with many different products, and few of them have relevant volumes," says Andrea Salvi, Process Engineer. The ability to generate the test programs in a short time is essential, along with the ability to quickly modify an existing test program incorporating the changes in the board layout that occur during the product's life. The flying prober's operating system can automatically generate the test program from the CAD data, without needing the intervention of the board designer, and this greatly improves the test line efficiency.

Miniaturized Components
Another important reason for choosing the flying prober is its ability to easily test the most miniaturized technologies: passives like 01005 and 0201, while RQFP ICs are contacted and tested with accuracy and repeatability, with no damage from the probe impact. "Testing would not be a problem with larger boards, where you can have all the test pads required," continued Mr. Salvi. "But on a PC board of 0.7, or even 0.5mm thickness, densely populated 2 x 1cm circuits generally do not have space for placing a test pad per net as recommended for Design For Testability (DFT). We have been able to take advantage of a cooperative program involving our design staff and SPEA's test engineers, aimed at developing a DFT that fits with our production. However, the product technology sometimes does not allow us to have the test pads. In this case, we have to use the VIAs, or the component pins."

The flying probe technology must guarantee the accurate and reliable direct contact to the component pins, with no damage on the board surface. This is made possible by probe movement technologies such as linear motors with magnetic guides and linear optical encoders on each Z, Y, and X axis.

Improving at the Source
At Datasensor, tested boards are removed from the SMT line and put into the supply line for the forward line, where the sensors are assembled. The assembled circuit is the principal part, that is then assembled with other parts and completed with a housing to produce the final product.

A defective PCB becomes a costly mistake if it goes to the final line, having value added with other parts and final box-build assembly. The cost escalates at the product is moved into the distribution channel and ends up in the end-user's hands. Therefore it is vital to keep this from happening.

"It is better to improve the process at the source, rather than detecting all the errors at the end of the line, with costs that increase at each step. We cannot tolerate more than a few faulty parts per million from the electronics department. The results we are obtaining with the flying prober make us think we are on the right track; we see a substantial decrease in the defects at the end of the line," explains Tomaselli. The goal is to reduce defects, in a closed-loop system that improves the overall efficiency of the production process.

"A process that works well from the beginning is more important than a variety of controls that detect the errors later. Early fault detection is essential; a reliable indicator of the generated defects is necessary to attain defect-free process. This is even more important since most of our production relies on components whose price has to be kept low: Too many controls would generate additional costs that would affect the profits," continues Tomaselli.
Flying probes in action.

As well as guaranteeing the product quality, the flying prober plays a fundamental role in the process control. What guarantees the return on investment is not the defect detection as much as the actions to stop generating the errors during the process. In this way, the flying probe test becomes more and more an indicator of the process quality.

Advanced Automation
Datasensor relies on factory automation, with advanced technologies, in order to have an efficient just-in-time management of orders and ECOs (Engineering Change Orders). Automation is used in the manufacturing, assembly and test lines.

The beginning of this year saw the purchase of a new high-throughput production line, comprised of the latest generation screen-printing and fast SMT machinery, operating in innovative handling lines that optimize the automated assembly and test of the electronic boards. The flying prober has been equipped with automation, providing automatic board loading and unloading from racks, and rotating the board so that it can be tested on both sides. Without the need for setup changes, the system can be used either with manual loading and unloading, or in full automation mode.

At the end of the assembly line, Datasensor placed two test stations: an automated optical inspection machine and the flying prober. "The flying prober gets much more use, since it works in fully automatic mode, without needing the constant presence of a human operator. Because of this, the optical inspection system has become a considerable bottleneck", declares Salvi.

Contact: SPEA America, 2609 S SW Loop 323, Tyler, TX 75701 903-595-4433 fax: 903-595-5003 E-mail: Web:

See at APEX Booth #2065.

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