The Natech team has developed a process to build a mold for microfluidics chips at a cost of $10,000. The lead time from production-ready CAD to samples is as low as four weeks. Pushing the boundaries of what is possible using conventional moldmaking and molding resources has allowed the team to remove time and cost drivers from the process.
As electronics continue to progress, the trend over time has been to move toward smaller applications as more is fit into less space. Fluidics has followed the same path as the industry pushes the boundaries of what is possible so that what has previously been done in a full lab can now happen on a single chip. This removes many steps in the process, reduces the chances for human error, saves time and money per test, and decentralizes the testing to get closer to the point of care.
As a result, fluidic channels have shrunk down to 500 microns to as small as 20 microns. In microfluidics applications the reagent introduction, fluid mixing, and fluid control rely upon extremely small features to control the fluid. Not only are the tolerances tight, but the flatness precision requirements are high because the channels depend upon a proper seal. Without a flat, even surface, the seal of the channel loses integrity, and the system fails.
The goal from a manufacturing perspective is to push conventional rather than specialized manufacturing methods to achieve scale of smaller features and tighter tolerances. Manufacturing using conventional methods would reduce lead times and costs.
In low quantities, incredibly small has been achieved using specialized methods. For example, a nickel mold insert can be fabricated using photolithography to create channels in the tens of microns in size. But scalability can be sacrificed which means additional costs and delays. The process from initial R&D breakthrough through full-scale manufacturing can be summed as: 1. Achieve it once, 2. Replicate it, 3. Scale it up.
What does this mean in practice? Making a handful of parts that work is a development milestone but not a manufacturing solution. Fabricating hundreds or thousands can be another milestone but not yet a fully scalable solution. Manufacturing using a specialized mold fabrication process helps to achieve scale but can come at the expense of cost and lead time.
Breaking the Rules
According to the published rules this should not necessarily be possible using conventional mold manufacturing, molding methods, and molding materials. Part of the challenge is that each material brings its own set of rules. For example, metals can typically achieve tighter tolerances than plastics. Different plastics families, different plastics grades, and even different plastics manufacturers can have different rules. In practice, these rules can prove to be somewhat arbitrary and overly general. When pushing the boundaries on what is possible, we can be oblivious to the rules and hope to get lucky, follow the rules without question, or break and redefine the rules.
The team had previously achieved 300-micron channels with successful performance and wanted to push further down. The A-Line collaboration included 250-micron channel width and a 2:1 aspect ratio of channel at twice the depth relative to width on a COC chip.
The Natech Process Engineer ran multiple iterations of Moldflow analysis to determine the optimal gating location. The mold was built and sampled in four weeks. The very first samples were filled, sealed, and the channels were successfully loaded with liquid without observable leaks.
Hitting the micro tolerances on the micro features using specialized methods had previously been accomplished. Doing the same at scale using only conventional manufacturing methods not only reduces costs and lead times but also improves the control of quality.