How Clean is Clean Enough to Achieve Reliable Electronic Hardware?


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The golden age of the Internet, digitization and social networking is in full swing. These technologies enable the Information Age from which every company and entrepreneur can cut costs, innovate new offerings and reach billions of new customers. Embedding information and telecommunication technologies in the form of sensors will increase productivity throughout the entire economy.

Information technology drives processing speed, memory storage and, ultimately, new capacity. Technology is constantly improving digital product innovations that are increasingly faster, more efficient, more useful, more affordable and more powerful. Speed is enabled from denser circuit designs, tighter pitch and shorter line spacing. The risk of residue present on the surface and under bottom terminations can impact chip performance at these shrinking dimensions.

Reliable hardware is more challenging to reproduce due to component size, residues trapped under bottom terminations, shorter distance between conductors, higher pinout devices in a smaller footprint, increased electrical field and environmental factors. There is no one universal test method for quantifying reliability risks. The amount and nature of the data generated depends on the product being produced, the consequences of failure and the end-use environment. A three-phase approach is commonly used to specify the manufacturing process requirements:

• Phase 1: Screening experiments with inexpensive test vehicles

• Phase 2: Validation experiments with more representative test vehicles

• Phase 3: Verification runs on manufactured assemblies

The purpose of this article is to develop an improved test method to measure the resistance on non-cleaned and cleaned test boards using low residue solder pastes under a series of bottom termination components. Testing the location, flux type, quantity and mobility may provide an improved risk assessment of reliability expectations.

The problem is that current chemical and electrical test methods limit the effectiveness for testing residues entrapped under component terminations. Residues under the bottom termination have the highest potential for leakage and are the least understood. Site-specific testing of the residue under the component termination has the potential to detect resistance drops. Gaining a better understanding of no-clean residues that do not outgas during reflow will help reliability engineers understand cleanliness at the interface.

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Editor's Note: This article originally appeared in the August 2015 issue of SMT Magazine.

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