How Profiling Technology Produces 100% Yields
By Dipak Patel, Owner/Manager, and James Boyd, Process Engineer, Krypton Solutions, Plano, TX
Krypton Solutions, a contract manufacturer in Plano, Texas operates in a highly competitive marketplace for electronics assembly services. The company prides itself on using advanced technologies to exceed its clients’ demands for high quality, cost effective solutions. To this end, Krypton Solutions made investments to enhance the capabilities of its reflow process in 2011, specifically the validation of the oven process by better measuring and documenting the profiles of the assembled printed circuit boards.
The company believes in using technology to provide a better solution for its demanding clients, while reducing the cost of production. It also strives to differentiate its company from other CMS organizations in this highly competitive market. One example of how this strategy plays out is represented by its investment in a real-time thermal process management system. The company realized that their reflow oven constituted a real challenge in terms of securing and documenting the requested PCB quality. The ultimate output from a reflow oven is to produce a PCB profile inside a specific process window, which is dictated by solder paste and component tolerances.
Essentially the reflow oven is a profile machine. The missing link in this profile machine is the measurement of the profile. By adding an automatic profiling system, the company no longer runs blind between spot checks and the production is no longer interrupted to perform such measurements manually.
Krypton uses a Heller 1913 Mark III – a sophisticated reflow oven that provides excellent control and stability. However, Krypton’s ultimate goal is to obtain the correct thermal profile for each PCB that it assembles. It soon became apparent that the traditional method of spot checking the thermal process left the company running blind much of the time. Beyond the production benefits associated with upgrading its thermal process to a best-in-class capability, it became apparent that there was a business opportunity – a chance to acquire new contracts from demanding clients who value process control and documentation. In addition the company wanted tools that could provide better information and insight into reflow processes that, in turn, would lead to both quality and productivity improvements. It was believed that once the company understood its ovens and could measure the behavior of the PCB profiles, it could improve upon them.
After its initial research, Krypton Solutions decided to purchase a continuous thermal management system for all its reflow ovens. The system the company chose was the KIC RPI and KIC Explorer with Auto-Focus. The RPI was installed on its three reflow ovens in April 2012. The KIC RPI uses built-in sensors in each oven to automatically measure the profile for every PCB produced. Each profile is displayed and stored in the oven’s computer. The stored profiles can be retrieved based on a date and time stamp or, alternatively, when the PCBs come equipped with bar codes, the relevant profile pops up when the bar code is scanned.
Krypton Solutions wanted to document the hard-to-get thermal profile information on an ongoing basis.
System programming is performed by an initial manual profile using the KIC Explorer, which doubles as a process improvement tool. Essentially, the tool reviews all possible combinations of oven zone temperatures and conveyor speed and selects the recipe that positions the profile deep inside the process window that Krypton Solutions establishes based on solder paste specs and component tolerances.
The KIC RPI automatically provides real-time profiles for each PCB as they exit the reflow ovens. The profile specs are measured against the established process window for each selected dimension such as peak temperature, time above reflow, slope and more. Because its PCBs tend to have a myriad of different components, the company can set unique process windows for each of the sensitive components even though they are on the same PCB.
Not only does Krypton Solutions get measurements of the profile on select components for each PCB, but the KIC RPI also automatically charts the profile specs on basic SPC graphs, including process capability (Cpk) numbers. Suddenly, the company has access to real-time process information and trends that, in turn, allow it to make better decisions regarding how the thermal process is run.
For example, Krypton Solutions no longer relies on automated optical inspection (AOI) or in-circuit test (ICT) to belatedly announce a problem — instead, out-of-spec situations are captured immediately. The company even has the potential to detect issues before they evolve into defects with a warning from the KIC RPI that the process is no longer in control.
The company’s semiconductor and medical clients have critical and sometimes expensive PCB assemblies that need to perform perfectly for years to come. These clients are now assured that their products are processed in spec, and Krypton Solutions has documentation to prove it.
Clients often request delivery of 100 percent of the assemblies, therefore no scrap is permitted.
Another challenging issue is that the company cannot sacrifice PCBs from repeated profile runs or mishaps in the oven. Its clients often request delivery of 100 percent of the assemblies; therefore, no scrap is permitted. The KIC Explorer with Auto-Focus enables the company to achieve that goal consistently.
One example relates to the initial oven setup. For a PCB assembly not previously produced, the software recommends the oven recipe prior to running a single profile. Krypton Solutions’ experience is that this initial oven recipe gets it close to the optimal value while one or two subsequent profile runs will yield the optimized oven setup. There is little risk of damaging the PCB on the initial profile run. Using removable aluminum tape to attach the thermocouples on the initial profile run eliminates the need to sacrifice the PCB for initial oven setup.
Frequent Oven Setup
Being a high-mix/low-volume CM means frequent oven setup for new assemblies. In the past, the company could spend up to a half day fine-tuning the oven before starting the production run. Today, it is down to a couple of hours and expects to further reduce that time as it moves up the learning curve with the new tools.
The fast setup time has been achieved through the accurate Auto-Focus prediction software that typically finds the best oven recipe within a couple of profile runs. The time consuming part of such fine tuning of the oven recipe is not the prediction part, which is performed within seconds, but rather is related to the time it takes the oven to stabilize on the new setting. Typically, oven zones can stabilize within a few minutes when the zone settings call for increased temperatures. Cooling the zones, however, may require 20-30 minutes or more. The trick is to avoid numerous “trial and error” reiterations, hence the importance of an accurate prediction software.
This challenge is amplified when replacing older ovens with new ones or when expanding to additional production lines. The company can have up to 100 different recipes with associated PCB profiles stored in each oven. Utilizing the Auto-Focus simulation software has made transitioning these to a new oven manageable.
The new window into the thermal process has enabled the company to optimize its thermal process with resulting improved quality and productivity. This technology has enabled Krypton Solutions to exceed demanding client’s requests while running its operation more cost effectively.
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