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How to Make a Negative Resist PCB

by: Mar 20,2014 775 Views 0 Comments Posted in Engineering Technical

printed circuit board PCB

A printed circuit board consists of a substrate upon which copper tracks connect electrical components. The copper tracks on a PCB can be very tiny -- 1 millionth of a meter -- which allows many electrical components to be combined into a small space. PCB boards are typically made using a process known as photo-lithography. During this process, light is shone through a stencil and the exposed parts of the substrate become chemically changed. In negative resist photo-lithography, the exposed parts of the sample remain after development, whereas positive resist photo-lithography leads to the removal of the exposed material after development.

Instructions

1 Place the substrate onto the spin-coater chuck. Using a pipette, place enough SU8 2002 resist onto the substrate to completely cover it. Program the spin-coater to spin at 500 rpm for 10 seconds and then 2000 rpm for 30 seconds. The manufacturer specification sheet states that this should lead to a resist thickness of 2.4 microns.

2 Remove the sample from the spin-coater and place it on a hot plate set to 95 degrees Celsius or 203 degrees Fahrenheit. Leave the sample on the hot plate for two minutes. Remove sample and allow to cool for five minutes.

3 Place the photo-mask into the mask aligner. Place the sample under the mask. Expose the sample. Remove the sample from the mask aligner and place it into a beaker of developer for one minute. After development, rinse sample in Isopropyl alcohol. The sample will now consist of a series of patterned pits, which copper can be deposited into to finish the PCB.

4 Place a pellet of copper into the evaporation chamber crucible. Pump down the evaporation chamber to a pressure of about 10^-6 mbar or 10^-4 Pascals. Deposit the desired thickness of copper. Remove the sample from the evaporator. Place the sample into a beaker of acetone. This removes the remaining SU8 resist, and leaves the copper tracks. Rinse the sample in a beaker of IPA.

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