This has all changed, and users are bombarded with a confusing array of brands, technologies, and suppliers. Today, with linewidths shrinking below 100nm and cost pressures at an all-time high, choosing the right filter for wet cleans can be a tricky process, requiring users to navigate through a river of not-so-straightforward and sometimes conflicting information.

It’s widely known, for example, that non-dewetting PTFE filters minimize the formation of gas bubbles (a form of contamination), but few are aware that some non-dewetting filters may, over time, release extractables that are just as damaging as the contaminants the filter is removing. It all depends on the filter manufacturing process, which end users rarely have insight into—unless they ask.

So, choosing proper wet clean filtration comes down to a matter of knowledge. There are no one-size-fits-all answers, but there are a few truths to keep in mind during the selection process:

 All Filter Membranes Are Not The Same

Today, the way a filter is manufactured is as important as the capabilities of the final filter product. Contamination levels from process chemicals are measured in parts per trillion, and filters must be capable of removing impurities from the process stream without contributing impurities that could be deposited on the surface of the device.

Of course, chemical filters must be manufactured and assembled in a controlled clean environment, but beyond this, users must be aware of how materials of construction are purified to reduce organic and inorganic extractables, and how membrane materials are modified to suit application needs—two key factors in whether a filter will contribute contaminants in the process stream.

Take PTFE filters, for instance. PTFE is highly inert but hydrophobic in its native state. In recent years, filter manufacturers have had to come up with proprietary methods of making the material less hydrophobic to reduce prewetting procedures and times, and to reduce and prevent start-up delays. However, depending on the process used, this alteration may change PTFE’s degree of inertness, increasing the risk of extractables.

Bigger Isn’t Always Better

In filtration, traditional thinking holds that more filter equals better filtration. This simply isn’t true anymore. While PTFE and PVDF membranes have been the material of choice for chemical applications, there are a variety of alternative filtration materials today, such as ultra high molecular weight polyethylene (PE) and polysulfone (PS), that make different filter sizes and shapes possible.

Unlike PTFE membranes, which are stretched, these alternative materials can be cast to create specific pore structures. Asymmetric cast membranes, for example, reduce flow resistance, allowing more capacity to be packed in a much smaller area than with traditional materials. In addition to reducing costs, this results in a smaller surface area, which inherently reduces the potential for defects and extractables.

We can look at it this way: A 10-inch length asymmetric membrane filter cartridge can produce the same flow rate as a PTFE (or PE) membrane filter cartridge that has as much as 8 sq ft more filter area. This area is equivalent to the surface area of the inside diameter of 50 linear feet of three-quarter inch tubing.

When you count the added surface area of the downstream support material, you’re up to the equivalent of 100 linear feet of tubing, and if you have multiple filters in your process, you could easily have the equivalent of over a mile of three-quarter inch tubing surface area that is in intimate contact with your process fluids.

Is this a problem? Hopefully not, but as processes become more stringent, it is the unobvious contamination sources that may be problematic. So, remember, bigger isn’t always better.

Filters Aren’t Just Consumables, They’re Process Enablers

This is perhaps one of the greatest changes in chemical filtration over the past decade. Today’s filters can make or break a user’s productivity and yield goals, and should be thought of in those critical terms. Not so long ago, when a new filter was installed on an acid tool, the filter would need to be purified, or flushed, with the acid until the purity levels were within specification. This could take several hours to days, wasting expensive acid and sacrificing uptime. But filter manufacturers have since developed ways to make today’s filters far purer than their predecessors, allowing users to minimize flushing time and achieve dramatic increases in uptime and throughput.

And tomorrow’s filters will meet even tighter purity parameters as filter manufacturers research, develop, and implement myriad novel purification methods (such as supercritical fluids, ozonated acids and water, and other techniques).

Moving forward, emerging technologies will call for more efficient and sometimes entirely new purification and separation techniques—pressing filter manufacturers to go even deeper into the research and development of new products, and presenting users with an increasing variety of filtration options to understand and master.