Today’s engineers are some of the best jugglers and slight-of-hand artists outside Barnum & Bailey. They must continually find ways to manipulate several competing requirements and still come out with a winning design.
Their challenge is to reduce product design cycles and costs yet improve quality. This is a tall order to fill even for the best of prestidigitators—but not impossible if environmental test tools help determine the efficacy of a design.
Environmental test confirms quality through simulation and product-life testing and often is a prerequisite to quality assurance. It is divided into climatic and mechanical environmental testing. Climatic includes pressure, humidity and temperature while mechanical incorporates shock and vibration.
Environmental test equipment subjects products and devices to appropriate simulations to determine the failure rate and how the devices respond to the severity of an environment. To keep up with today’s electronics, your test equipment, which includes the thermal chamber, shaker, controller and software, must change with your needs.
Environmental Chamber Updates
Some users are retrofitting environmental chambers with the latest non-CFC refrigerants, said Tom Patterson, national sales manager at ESPEC. These companies are making the decision based on corporate environmental-awareness policies.
The most opportune time to make the change to non-CFC refrigerants is when you experience refrigeration problems, continued Mr. Patterson. The old-style refrigerants are more expensive to replace than the newer types.
Some manufacturers regard a conversion to liquid nitrogen (LN2) as worthwhile because it allows faster thermal cycling to meet the more robust test requirements. Often, injecting LN2 and adding extra banks of heaters is the only viable method to update some thermal chambers.
However, it may not be appropriate to use LN2 if your test area is not set up to supply large amounts of the liquid refrigerant, said Mr. Patterson. Also, the number of heaters you can have is limited by the electrical design and the space available.
For wafers and chips the move is toward testing at-temperature in a production environment to intercept failures before the devices are packaged, said Tom Gerendas, president and CEO of Temptronic. The process requires a thermal chuck that can cope with an automatic prober operation. For example, wide horizontal swings by the chuck stage require flexible coolant lines and air-cooled chucks to prevent moisture leaks.
The increasing geometrical density of wafers and power dissipation per square millimeter lead to an undesirable concentration of heat in micron-size areas, said Mr. Gerendas. New thermal mapping techniques are available for chip designers to observe temperature distribution with 0.1°C and 1-micron resolution.
Today’s more complex packaged devices have higher pin counts and higher frequencies. Users are requesting high-low-ambient temperature testing capabilities to cope with these, said Mr. Gerendas. Tri-temperature testing often is requested for production-floor operations, and it requires that airflow velocity of the temperature- forcing equipment be increased to cope with throughput needs.
Vibration Equipment Updates
The most significant update issues for vibration equipment are multiparameter monitoring during lifetime tests and multiaxis testing, said Paul Ibanez, principal at ANCO Engineers. Multiparameter monitoring subjects a component to mission stresses until failure, and monitors specific performance during the whole test period. It includes logging of temperature, pressure, performance, leakage, force, torque, current and voltage. The goal is to understand the process leading to the failure.
There is increasing interest in multiaxis testing for some applications including automotive, seismic and nuclear power plant electrical equipment, said Mr. Ibanez. More manufacturers are requesting two, three and even six axes of vibration to better define an environment and duplicate failure modes.
The controller requirements for vibration equipment include analog sine and random, multitone sine, sine on random and tests requiring phase-dwell tracking, said Robert Mercado, sales and marketing engineer at Trig-Tek. When phase control is critical, customers request instrumentation to run multiple electrodynamic or hydraulic shakers simultaneously.
Single controllers now can coordinate the operation and test sequencing of environmental chambers and shaker systems, said Dave Galyardt, product marketing manager at Spectral Dynamics. The central controller issues commands and monitors status via gated TTL logic lines or RS-232 and RS-485 serial lines. It can change the chamber temperature or pressure, and initiate a vibration test in an automated sequence.
Some products provide improved controller operation such as the 48-bit digital signal processing (DSP) architecture of the DVC48 from Ling Dynamic Systems. It supports Windows 95, NT and multitasking functions so operators can fully use test run time to compare, review and analyze data.
Recent advancements to some shakers include protection for the equipment as well as the product under test, said Mr. Mercado. Some users think that if a computer is running a vibration test then nothing can go wrong.
This is incorrect. Operator error and a faulty switch are only two possibilities that can cause a computer to run in an overtest or undertest condition. Sometimes this is not found until after the test, requiring a retest or expensive product analysis. Other times the condition is noticed immediately because the shaker hits the safety stops or there is visual damage to the product.
A separate and redundant safety capability is needed to assure proper force levels are applied to protect shaker systems and products, observed Mr. Mercado. The need for shaker and product protection is especially apparent when testing one-of-a-kind expensive products or when performing production environmental stress screening.
Pros and Cons of Automation
Automation of the environmental test process increases productivity and enhances product quality by providing better control over test operations, said Mr. Galyardt. It also improves access to statistical process control information.
The automated test does not have to be babysat, which uses valuable personnel time, said Chris Hanse, vice president at Hanse Environmental. But ask these questions before implementing an unmanned process:
Will I always be testing the same product?
What will be the effect if something breaks down in the process?
If something does go wrong, can I provide extra safety so little else is affected?
How much human interaction will I need? Will I need skilled or unskilled personnel?
Automated production-line environmental testing is an uncommon application, said Mr. Patterson. There are many complications and compromises that must be resolved before automation can work. The most significant hurdle is the cost of the equipment. For example, automated equipment can easily double or triple your capital investment.
An alternative is batch testing, observed Mr. Patterson. You can test enough product at one time to meet the demand without investing in costly in-line automated equipment.
Automation has a number of drawbacks, agreed Mr. Gerendas. These include:
The cost of thermal equipment and prober accessories is high.
Thermal tests usually slow down probers, testers and handlers.
Modifying ambient-test programs to include additional test temperatures is expensive and requires significant effort.
Handling, datalogging and part damage increase when all components must be re-run at each test temperature.
Thermal test equipment requires additional floor space.
Users are under extreme pressure to reduce product design cycles while lowering costs and enhancing quality, said Mr. Galyardt. Some products, such as the PUMA Vibration Control System from Spectral Dynamics, are designed to help you use your time more efficiently. The program is multitasking so you can simultaneously run a test, analyze the data and compare the new data with previous information. You do not have to be on the same computer or network, which allows you to acquire data from across the lab or across the country.
Fast temperature cycling is a hot topic, continued Mr. Patterson. It helps inexperienced companies determine the failure rates of their products quickly. For those companies with no product failure-rate information, the thermal-shock process
is a popular starting point to get higher transition rates without resorting to the LN2-type chambers.
The multifaceted requirements to reduce costs and time to market while improving product quality certainly challenge engineers. But the environmental test process will help you juggle demands while controlling your product design.
Environmental Test Equipment
Servo Shake W Tables Designed
For Automotive BSR Testing
The R030 through R230 series of servo electric and hydraulic shaker tables perform buzz, squeak, rattle (BSR) and durability testing for the automotive industry. The servo-electric version has <55-dB noise, is transportable, has three or six axes and does not require a special foundation. The mechanical-actuator design features three axes and produces sine and random motion, and can be upgraded to a servo motor driving six axes. The servo-hydraulic version supports three and six axes with a capacity of 2,000 lb on a 6’ × 8’ table. ANCO Engineers, (303) 443-7580.
System Allows Remote
The CASS Thermally Conditioned Airstream System provides environmental stress screening for components. The system can be combined with a support frame, a motorized chamber and a shaker table to apply thermal and vibration screening. The system provides a temperature environment from -100°C to +200°C. Remote operation is possible via the IEEE 488 interface. Environmental Stress Systems, (209) 588-1993.
Chambers Suited for Profiling
And Prequalifying an ESS Program
The ESS5 and ESS11 Environmental Chambers are small-volume units designed to test a few boards at a time. They can prequalify an ESS program, and find ideal temperatures and change rates for products. The chambers feature non-CFC/HCFC refrigerants and a variety of control systems, refrigeration sizes and product fixturing options. ESPEC, (800) 537-7320.
Walk-In Oven Supplies
Temperature to 200°F
The No. 782 Walk-In Oven is humidity controlled and electrically heated to a maximum temperature of +200°F. The workspace measures 8’ W × 13’ D × 8’ 8″ H. The chamber has two 7,800-cfm, 5-hp recirculating blowers for downward airflow. A 6,000-cfm, 5-hp exhauster enhances circulation, and a two-pen recording controller monitors and governs the temperature and humidity. Grieve, (847) 546-8225.
Memory Test/Burn-In System
Has Distributed Architecture
The GEN-1 Parallel/Distributed Test and Burn-In System has a processor, two driver boards and a regulator board. It accommodates 16 modules with 64 DUTs to test up to 8,192 devices. The system features ±2-ns edge-placement accuracy, 128 drivers/receivers with up to 512-kB memory for each channel, 28 address lines, ±2-ns skew between sockets and an on-the-fly timing change capability. KES Systems (602) 431-1760.
Is Based on 48-Bit DSP
The DVC48 Vibration Controller is a Windows 95 and NT compatible board based on a 48-bit DSP architecture. It supports complex sine, random and classical shock applications. Programs run simultaneously on the multitasking controller so you can review, compare and analyze data from tests. A context-sensitive on-line help facility is provided. Multiple controllers and PCs can connect to your network for remote testing. Ling Dynamic Systems, (011) 441-763 242424.
Incorporates Digital Control
The PUMA™ Vibration Control System meets test requirements for random, sine and shock up to 10 kHz. It incorporates digital vibration control methods and data- acquisition and signal-generation hardware based on DSP technology. The system uses the company’s Computer-Aided Test Suite architecture with Pentium- and Windows 95-based computers. It has four channels expandable to 16, a 90-dB dynamic range and a frequency range from 50 Hz to 20 kHz. Spectral Dynamics, (408) 474-1700.
Hydraulic Tester Offers
Six Degrees of Control
The CUBE™ Hydraulic Test System offers six degrees of control to replicate vibration environments including those needing very high frequencies. The system is available in force ratings from 4,500 lbf to 35,000 lbf for each axis. Six shakers provide control of the six degrees of freedom to 250 Hz. Expander heads increase the mounting surface to 60 in.2. Applications include squeak and rattle testing of automotive parts and screening of electronic components and modules. Team, (360) 757-8601.
Thermal System Meets
The TP04200A ThermoStream System meets EU, UL, VDE, SEMI and CSA thermal requirements with a temperature range from -80°C to +225°C. The air heating and cooling capacity is 9 liters/s continuous airflow and the temperature control is 0.1°C. Applications include testing components, hybrids and modules as well as providing thermal profiles for multichip modules, PCBs and small subassemblies. The ATE-compatible unit has IEEE 488, RS-232 and ST/EOT/SOFF interfaces. Temptronic, (617) 969-2501.
The Model 2050 Multi-Tone Vibration Controller supplies sine excitation and control for electrodynamic and hydraulic shaker systems requiring input frequencies from 1 Hz to 20 kHz. The sine tones can be divided into 25 frequency segments to provide a specific vibration profile. The segments control acceleration, velocity or displacement. Servo compression speed is programmable in the sine profile from 1 dB/s to 250 dB/s. Linear sweep rates in Hertz per second and logarithmic sweep rates in octaves/min are provided. Trig-Tek, (714) 956-3593.
Closed-Loop Control Software
Puts Data in Time Domain
Time Replication Acceleration Control is a closed-loop method for electrodynamic shakers that allows reproduction of acceleration data in the time domain. It is available as an option for the company’s UD-VWIN vibration control system. The software stores up to 10 minutes of acceleration time waveforms and zooms from 1 frame to 1/8 frame. Applications include buzz, squeak and rattle testing, accelerated life testing; endurance testing, and environmental conditioning. Unholtz-Dickie, (203) 265-3929.
Copyright 1997 Nelson Publishing Inc.