SEPCON assembly – written description

Following is a written protocol for SEPCON assembly.  (Here is a link to a video demonstration)

Materials required: wafer tweezers, small sample tweezers (preferably plastic), soft foam board from craft store, wafer of sepcon chips, razor blade, plastic enclosure to store complete SEPCON, top basket, bottom basket,  300 µm thick silicone sheet of pre-cut “U” and square shaped gaskets.  (outside length – 5.5 mm, inside length – 4.0 mm)

Popping chips out of a wafer is a time consuming and delicate task.  The membranes are relatively fragile and the forces applied to break out the chips can lead to their destruction.  Begin by slightly elevating the wafer on one side using the wafer tweezers.  (a few millimeters may suffice)

Next,  glide the plastic tweezers along the seams between chips while gently applying pressure.  Try to identify a weak seam and focus on that region, removing a section comprising multiple chips as opposed to removing a single chip.  It may take several passes, gradually increasing pressure as the seams are weakened.  The greater the pressure applied, the more likely an abrupt separation will take place which often results in membrane damage and debris creation.

Once a section with multiple chips has been separated from the full wafer, place the wafer back in its holder and focus on the section of chips.  Using the wafer tweezers, elevate one side of the section and again apply pressure with the plastic tweezers at the seams between chips.

Now that the chips are separated, it is necessary to visually inspect the membranes using an optical microscope.  It may be possible to tell by eye if there is damage, but very small defects will only be visible under the microscope.  Below are example images showing a perfect 5 slot SEPCON  and a damaged SEPCON.  The slot with a  broken membrane is allowing the front side illumination to pass directly through, making the slot look black.

Below are backside illuminated images which are useful sometimes, depending on the membrane being inspected.  (The camera reduced the quality of the image significantly)  In this case, it is nearly impossible to differentiate between the intact membranes and the broken membranes.

The gaskets below are cut from a sheet of silicone 300 µm thick using a Silhouette brand cutter.

Place a “U”-shaped gasket into the bottom basket oriented with the open ends facing the same direction.  This will allow filtrate to flow out of the the assembly once completed.

Once the “U”-shaped gasket is firmly and evenly placed in the base of the bottom gasket, place a SEPCON chip on to with the “bottom” side up and the slots running towards the opening in the basket.  The “bottom” of the SEPCON can be determined by looking for the indented, trench-like look of the slots.

 

Next, place the square gasket on top of the SEPCON chip, trying to keep the gasket flat and centered.

Next, the top basket is snapped into the bottom basket.

Note: The square base of the top basket has three sides with longer plastic ridges that will lock into the bottom gasket.  One side has a shorter ridge and this must be orientated towards the open end of the bottom basket to allow for fluid to escape the assembly.

Try to put evenly distributed pressure on the top basket as it snaps down into the bottom basket.

Next, cut an “X” in the cap of the  plastic housing.  (This is to ensure that a pressure differential isn’t created between the top and the bottom of the SEPCON.)

Finally, place the SEPCON assembly into the plastic housing and seal with the cap.