Cleanliness Verification
Each year the need for stricter cleanliness levels for cleaned parts is discovered. One professional may work in the semiconductor industry, where critical dimensions are shrinking every hour, or so it seems. Another professional may work in the automotive industry, where it is being learned that the initial operation of an engine will determine its life expectancy.
In all cases, the tolerable level of contamination is constantly decreasing. The problem is, how to measure this contamination? With the exception of the semiconductor wafer, most contamination sensitive parts are complex in shape and therefore do not lend themselves to traditional scanning techniques; therefore, different methods need to be used when testing these items. Let’s take a look at the three more common techniques currently used and discuss the advantages, disadvantages and benefits of each.
One of the common themes in each of the extraction and evaluation methods described is time and labor. An operator must be intimately involved in each step of the test. They must clean the sample test chambers, perform background checks, extract the particles, and measure the contribution by the test part. As the cleanliness requirements increase, measurements at smaller particle sizes will be necessary, which increases the time required to clean the apparatus. Because of the labor and time requirement, these tests are limited to laboratory checks.
Parts are removed from the cleaning system and sent to the lab for testing. The results of these tests may not be available for a day to a week later, depending on workload in the lab. Indeed, many industries only use these methods when experiencing a major problem in yield for this reason. Some opt to skip the testing completely in favor of shotgun servicing of the cleaning equipment. The rationale is that by the time the results point to the actual problem, enough productivity will be lost to merit the more rapid, but expensive, equipment maintenance. These limitations produce extremely expensive repercussions in the manufacturing process when parts must be recalled or re-examined to prevent reliability problems in the customer’s hands. Also, at best, these methods offer a very small sample of the overall control in the cleaning process. New technologies that help maintain high throughput make it possible to move testing out of the laboratory onto the manufacturing floor. Many advantages are realized by performing the testing right in the manufacturing area, when the parts exit the cleaning system. Foremost, contaminated parts can be eliminated from reaching final stages of manufacturing. This will reduce or eliminate product recall/rework due to contamination failures. Additionally, increased information is available about the performance of the cleaning system. Filter changes, bath changes, and major maintenance can be performed only when necessary, all of which increase the tool’s up-time and utilization rate. Changes to the cleaning chemistry, or routine, can be immediately verified for benefit/detriment to the overall cleaning process. Permanently implementing only changes that benefit the cleaning process lead to better results in manufacturing
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