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February, 2020
The Importance of User Objectivity in Process Control
By Charlie Fujikawa, Senior Sales Engineer, Seika Machinery, Inc. O
ver the past 10 years, the SMT industry has made many technological breakthroughs and improvements to the production
process. Chips, packages and BGAs continue to get smaller, with finer pitches. The equipment contin- ues to get faster with increased precision. Now, more than ever, there is an increased need for manufacturing sites to increase productivity and efficiency. One integral step in increasing produc- tivity, is to decrease losses due to errors. This may seem like a no-brainer, but it is often easier said than done. Process control can help reduce, and often solve, production errors. All manufacturing sites have some level of
process control. This is the process in which we can ensure that the components of the production are working optimally. When we find errors in the pro- duction, we can trace the source using process con- trol to eliminate different factors that can con- tribute to the error. Eliminating trouble areas in these key points in the production allows for in- creased efficiency in troubleshooting. This is where we come across a very common
problem with a lack of process control. Many man- ufacturing sites depend on operator subjectivity to determine whether a process is acceptable or not. As the operator changes from site to site, or even shift to shift, there is no standard to judge the process objectively.
Controlling Paste Viscosity Solder paste is a critical component of the SMT
process, and it can be a key factor in production ef- ficiency. However, one major aspect of solder paste that is often overlooked is its viscosity. There are a number of different manufacturers that manufac- ture solder paste for SMT production. All the paste
manufacturers use a standardized testing method (most commonly IPC or JIS testing) to assure their paste meets an industry standard for production.
In an uncontrolled process, an operator will
take the paste out of the refrigerator, and leave it out to thaw for at least a few hours, waiting for the tem- perature to reach 77°F (25°C) (standard production temperature). The time is dependent on the temper- ature and conditions of the manufacturing location. Next the operator will use a spatula to manually mix the paste till it “looks” or “feels” mixed and ready to use. This process is dependent on the operator’s judgement of the paste’s condition. How do we know the paste is at the optimal temperature, viscosity, mixture, and condition for production? If the paste is too viscous, the material can
stick to the stencil and leave divots, canyons, and/or peaks in the solder pads. If the paste is not viscous enough, the pads may not hold their shape and slump, leading to solder bridging or low wetting ten- sion/force. Production runs could yield different re- sults, depending on who makes the judgment calls on the solder paste conditions. To help battle this, as well as troubleshoot issues, many manufacturers are requesting traceability data be recorded for all stages and processes in the production.
Automated Paste Mixing Automating this process makes the user cer-
Malcom PCU-285 spiral viscometer. Each paste is created and verified to be used
within a specific viscosity range for optimal produc- tion conditions. Once the paste is shipped and re- frigerated, the viscosity and condition of the paste changes. Viscosity is directly related to the temper- ature of the paste. In many cases, when the paste is ready to be used in production, it is taken out of re- frigeration and needs to be conditioned for use.
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tain of the solder paste’s readiness for production. An automated paste mixer, such as the Malcom SPS line of paste mixers, allows the operator to take the paste out of refrigeration and prepare it for production in a fraction of the time. The paste mixer will not only fully mix the
1/8/20
paste, but it will also bring the paste up to room temperature. The user will not have to worry about air bubbles, flux separation or inconsistencies in viscosity or temperature. Once the process has
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