Pan Pacific Symposium Conference Proceedings


IMPORTANT CONSIDERATIONS IN PACKAGING A SMALL HALL-EFFECT SENSOR

Authors: Ron Molnar and Jeff Wise
Company: AZ Tech Direct, LLC
Date Published: 1/26/2010   Conference: Pan Pacific Symposium


Seika Machinery, Inc.

Abstract: A Hall-effect (magnetic) sensor detects small AC or DC magnetic fields. A new design of a Hall-effect sensor has increased sensitivity to magnetic fields, even before amplification, allowing the sensor to be used for new applications, such as small-motion detection, trace substance detection, and other novel medical devices. In the case of this new sensor, small physical size enhances or enables performance in certain physical applications. The packaging objective, as with most integrated circuits, was to assemble the Hall-effect sensor chip in the smallest, high-volume package available without sacrificing reliability and performance at the lowest total cost solution. Major cost factors were die prep, package type/materials, assembly labor and overhead, final test, and packing methods. More precisely, the challenge was to specify and qualify one or more popular 4-lead to 6-lead “standard” plastic packages for a small ~250 µm x ~250 µm GaAs die that could be assembled and tested by multiple contract manufacturers in high volumes for a “die-free” cost of less than 2 cents each. The desire was to specify a RoHS-compliant package that met Level 1 moisture sensitivity without severely impacting the cost of subsequent board assembly. An overriding constraint was to select a package that contained no ferro-magnetic materials.

The search for an appropriate package and assembly facility, the issues encountered during assembly of qualification lots, the assembly process control data, and the chip/package reliability test results are described in detail. The individual constraints on the packaging, in and of themselves, are achievable with today’s technologies, however in combination they limited the choice of packages, direct materials, and suppliers. The trade-offs made, the merits and disadvantages of each approach, and the ultimate decisions and results are described. Details of the final package construction, die preparation issues, the assembly qualification build, and environmental reliability test results are revealed. A total cost analysis of wafer fab and sort, die prep, assembly and final test, and packing is presented.

Initial work in developing this new Hall-effect sensor showed that the die size could be shrunk significantly, thereby reducing the current path width to as little as 0.5 µm without sacrificing performance. Thus, the size of the future sensor chip designs will be limited only by the minimum contact (wire bond or flip chip) pad sizes and their minimum pitch dictated by assembly design rules. The drive for ever smaller Hall-effect sensors will push the limits of conventional small-scale package manufacturing and may result in wafer-level packages if the cost targets can be met. Ongoing research and development is focused on low-cost, flip chip implementations in which the cost of die rework vs. the cost of sub-assembly scrap will be considered.

Key words: Hall-effect, GaAs, SC70, package, assembly



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