Amkor has long been engaged in testing across multiple generations of a wide range of MEMS sensors. Early applications ranged from ink jet printers, DLP™, automotive inertial sensors and biometric sensors. These packages tend to be custom and / or proprietary as are the test solutions and flows.  As sensors have expanded into consumer applications and more standard packages a much greater focus has been placed on reducing the cost and complexity of test. At the same time there has been a large increase in the types of devices (low G inertial sensors, microphones, tire pressure monitoring, electronic stability control, safety systems, e-compass, altimeters and barometers).

The next trend will be combinational sensors such as an accelerometer and a gyro and an e-compass. All this makes for a challenging environment for test solutions that need to cover the stimulus, the conversion of physical real world analog signals into electrical data and processing of the data to determine if the product is good or not.

Amkor is experienced and well positioned to address today’s sensor test challenges and future devices. We offer a wide range of testers, handling equipment, product/test engineering support, test development and close partnerships with leading equipment makers. Through close alignment with our packaging engineers we make sure the critical test hardware designs are perfectly matched to the package for high first pass yield and robust test quality. Across all phases of the product lifecycle, Amkor develops the appropriate test strategies and cost reduction paths to help our customers succeed in their markets.  In 2011 we tested over 200 million units of sensors.

Here are some additional details on just some of the devices we’re testing and our roadmap:

• Automotive grade gyro meters
  
  • +/- 50 degree and +/- 300 degrees / second yaw rate
  • Up to 2,000 G shock survivability, 105C operation
• Accelerometers
  • Single axis high g to +/- 250 g, Dual axis low cost to +/- 1.2 g, high g to +/- 70 g
  • Up to 2,500 G shock survivability
• Single, Dual and 3 Axis magnetic sensors , Hall Devices and 3 axis e-compass
• Testing of low G accelerometers in > x70 parallelism  

Sensor Test Roadmap Summary

In the early phases of engagement with Amkor Test, we collaborate with our customers to formulate a winning test strategy. The starting point may be to leverage an existing lab or bench test solution and then scale it into a highly automated mass production test solution. In other cases, we can develop the stimulus and work with our equipment suppliers and our own development engineers to make the important “make versus buy” decisions to deliver the right solution.

For example in the area of e-compass or magnetometers we performed a “make vs buy” analysis and decided to develop our own solution to deliver a lower cost of test with several novel features. Existing industry solutions only covered 2 axis magnetic stimuli. For a 3 axis device this leads to a tripling of test time as three passes and re-orientation are needed (XY, XZ and YZ). Several commercial solutions relied on permanent magnets. The disadvantage here is that zero gauss offsets lack the needed accuracy.

Amkor’s magnetometer solution features a simultaneous, 3-axis, solid state, continuously varying magnetic field (0 gauss to +/- 10 gauss). This allows for zero gauss offsets, die rotation measurement and gain / sensitivity trim. The test software supports open/shorts, I2C sanity tests, standby & active DC current measurement and device customization (such as I2C slave address and NVM fusing). Our initial solution is quad site (x4) and scalable to octal site using commercial bowl feed turret handlers with integrated tape and reel. Test times under 2 seconds per device have been demonstrated.

Other aspects of test development, production and customer support include:

• Full bench Characterization (temperature, AC/DC & digital)
• Simulation Tools
• Application Specific Stimulus Design, Stimulus generation & integration
• Trim and offset Calculation during test
• Scalable and cost efficient test  solutions and roadmaps
• Data collection & correlation between bench and ATE
• Multi site testing (calibration, mapping, ID management)
• Advising on Design for Test
• Handling Methodology (noise and stress management)
• NIST quality standard part generation

Amkor fully understands the importance of lowering the cost of test and working with our customers to continuously improve the test coverage and solution across the product lifecycle up to the point of diminishing return. We attack these issues early on with appropriate equipment selection including the potential re-use of existing test assets. Amkor also carefully considers and develops a path for higher parallelism (multi site test) to take more cost out of test. Multi-site solutions are complex and careful cost benefit analysis is performed. We are the world leader in outsourced strip test technologies – which are now applicable to some types of sensors.

Here’s an illustration of cost reduction strategies: