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Setting Test Straight With A Novel Fixture Solution
Tilt Fixture Technology system jointly developed between Checksum and ECT,
By Staff of Everett Charles Technologies, Pomona, CA
In-circuit-test (ICT) fixtures have been a cornerstone of electrical testing for the past several decades. However, there have been few, if any, significant advances in this field over the past 20 years. ICT fixtures have steadily become more complex, which in turn increases the turnaround time and cost of developing them for an end user. Many companies have switched to using flying probers for testing at a new product introduction (NPI) for these reasons. The reality is that ICT fixtures, due to the high cost of these test fixtures, cannot be justified in most cases for NPI or low-volume-production applications.
But test fixtures are crucial to testing loaded printed-circuit boards (PCBs), and the Test Fixture Group of Everett Charles Technologies (ECT) is a leading manufacturer and customizer of fixtures for testing loaded PCBs. Well known for its innovative solutions, the Test Fixture Group has been awarded more than 20 patents for products and processes related to test fixturing. The company's latest development in measurement technology, a probe wireless fixture, was designed along with CheckSum (www.checksum.com), a leading provider of loaded PCB test systems.
Now, the ECT engineering team has created a major advance in ICT fixtures which it calls Tilt Fixture technology, a new fixture solution that is (a) more accurate, (b) significantly less expensive, and (c) can be manufactured in two to three days instead of two to three weeks needed for conventional ICT fixtures. This is accomplished by eliminating the wires in the test fixture and using the proven technology of ECT's ValuGrid
fixtures. These fixtures have tested billions of bare boards and our engineers leveraged this technology to meet the needs of the loaded board test market.
Nonmultiplexed Pin Architecture
In the past, ECT and CheckSum have worked together as mutual suppliers. ECT chose to partner with CheckSum because it needed robust pin electronics with high node count capability and, most importantly, a nonmultiplexed pin architecture. ECT's Director of Engineering & Operations, Gary St. Onge, explains that "so far, the partnership has been very beneficial. As our partnership has developed, we also have added CheckSum's MultiWriter On-Board Programming technology to the tester."
Mechanically, the fixture consists of accurately positioned horizontal plates with holes drilled in each layer to guide the Tilt Pins (thin solid pins) so that they contact test points on a unit under test (UUT) and the appropriate tester resource via the probe field. Proprietary software determines the connections and calculates the locations of the holes to be drilled into each plate. While most Tilt Pins are vertical or quite close to vertical, holes can be drilled in the various layers to guide the Tilt Pin on an angled path. This is done to facilitate hitting test points on a fine pitch or to access tester resources that are not located directly beneath the test point. The fixture achieves extremely high pointing accuracy and allows the company to also contact 15-mil (0.381mm) targets on 24-mil (0.6096mm) spacing. This is significant because this cannot be done on any other in-circuit tester.
Tilt Fixture technology provides three key and distinct benefits:
Faster fixture-development turnaround time.
The capability to hit targets as small as 15 mil (0.381mm) on 24-mil (0.6096mm) centers.
Fixture costs that are 60 to 70 percent lower than the costs of traditional ICT fixtures.
These unique benefits generate tremendous value and make it practical to use Tilt Fixture technology for NPI and low-volume-production applications. An additional benefit is that Tilt Fixture technology offers the test coverage and speed of ICT fixtures to a market currently serviced by flying probers.
While the cost of an ICT system is much higher than the cost of an individual fixture, over time, the cumulative costs of using many different individual fixtures can be many times higher than the purchase price of an ICT system. So, an opportunity to reduce fixture costs by 60 to 70 percent (with Tilt Fixture technology) is a revolutionary proposition.
Unfortunately, for many low-volume and NPI manufacturers, the cost of an ICT fixture is prohibitive for most projects, given the low number of units produced or the short period of time in which the product design may be fixed. For such projects, manufacturers are left with a poor set of choices: rely on functional test and pay for an army of technicians to debug failed boards or buy an expensive flying probe system. For many, the flying probe system is the solution. While flying probe systems do provide a base level of test coverage, they cannot match ICT test coverage. And, though they appear to be "fast," flying probe systems are extremely slow when compared to ICT systems. As more and more projects are shifted to the flying probe for testing, the limited throughput of these test systems quickly becomes a bottleneck.
The overuse of flying probe systems for low-to-medium-volume production boards is prone to creating bottlenecks. Tilt Fixture technology offers the throughput of traditional ICT systems, but with quick-turn fixtures to match the requirements of NPI applications. In a low-to-medium-volume production environment, one Tilt Fixture system can achieve the throughput of 5 to 10 flying probe systems. Also, Tilt Fixture technology does not suffer the maintenance issues and costs associated with the moving parts in a flying probe system.
During development of the Tilt Fixture systems, the engineers designed options that will allow users to expand coverage beyond basic ICT capabilities. Power-on functional test, boundary scan, on-board programming, and even use of third-party external instruments all are possible for Tilt Fixture systems. Customers may start with these test technologies or add them after production is stable. "Over time, we believe users will begin to consider trading in their 'Big Iron' ICT system for Tilt due to the quick turn, low-cost fixtures," added St. Onge.
Ultimately, ECT envisions that Tilt Fixture technology will help its customers more quickly develop and successfully test their products. The firm also believes that the reduced cost of creating test fixtures will enable customers to save budgetary funds for investments on technologies that will improve test coverage on their critical projects.
Contact: Everett Charles Technologies, 700 East Harrison Avenue, Pomona, CA 91767
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