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01/10/2007
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Solder joints account for a huge proportion of failures in electronic systems in all industries, writes Roger Bishop. But in the automotive sector where, in terms of cost, there is more electronic content in a car than steel, long-term reliability is more than a goal. It is a requirement.
At Delphi in Kokomo, Indiana, a group of engineers led by Dr Mahesh Chengalva provides analysis services to Delphi design engineers all over the world working on the next generation of automotive electronics. He has developed a set of tools on a web-based system that run simulations and provides answers on reliability and durability in the minimum time possible.
“The single largest driver of failure in electronics systems in the field is the repeated temperature cycling the product undergoes,” says Chengalva. “Eventually, in this harsh thermal environment, a solder joint will develop a crack, and we want to be able to predict when that will happen.” Given that the daily production of solder joints at Delphi is about one billion, the task calls for some very special tools.
For analysis power, Chengalva’s group relies on advanced non-linear solving capabilities of Abaqus simulation software from Simulia at Dassault Systèmes. To speed analysis throughput, Delphi design engineers have direct access to the Abaqus solver through a turnkey web-based expert system called D-Cube – the brainchild of Chengalva and Scott Baxter, a former Delphi colleague.
Along with the material model, Chengalva’s group has developed a library of pre-built thermal-cycling reliability models for many families of electronics devices, ranging from single components such as capacitors and resistors to full packages such as ball grid arrays, flip chip assemblies and surface-mount ICs. To validate the FEA models for each electronic package, the team simulates a set of thermal cycling tests and compares the results of simulations with the results of tests.
Should a designer need to select, say, a suitable ball grid array package from a number of suppliers, all he has to do is open the thermal tools section in D-Cube, click on the ball grid array icon, fill out an online form with input parameters, and hit submit.
The next step, FEA modelling, has been automated to cut pre-processing time from several days for complicated assemblies to about an hour. Finally, the input deck goes to the Abaqus solver. Complex three-dimensional simulations might take three or four days of continuous run time.
“Once the simulation is complete,” says Chengalva, “the design engineer receives a reliability value.”
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Author
Roger Bishop
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