UV LED PC Board Exposure Build
Using 1watt STAR UV LEDs To Photo Expose a PCB
There are lots of solutions available to expose the photo-resist of a PCB, but few, if any, can fully expose your board in 30 seconds or less. Read on for details on the build of a UV Light Source capable of exposing photo-resist or for the UV curing of different paints and finishes.
Photo exposing a PCB is a quick way to produce low-quantity designs and can be done by the experimenter at home relatively inexpensively. We recently had a client who wished to do exactly this, but wanted the ability to rapidly expose and process numerous one-off designs but they required a UV light source to expose presensitized boards.
The board they are using is made by MG Chemicals and is their Model 687 which is a Single Sided Presensitized 1/32" Copper Clad Board 100mm x 150mm (approximately 4" x 6"). This model of board comes presensitized and incorporates a peel-off layer protecting the sensitized copper base.
The solution they finally built and utilized was an exposer setup incorporating twelve 1watt STAR UV LEDs. The twelve LEDs are divided into four parallel strings of three modules, each connected in series being driven by a 1W LED driver.
MG Chemicals sells a florescent light source for developing the boards, but it was deemed that this process was too slow and at the time, the client was not able to source this product. A little researched shows the output frequency of the lamp is at 375nm and that generally any emitted energy in the 350nm to 450nm range would be more than ample to expose the boards. The UV STAR LED selected for this project has an output frequency of 400nm to 410nm which was right in the center for the desired frequency spectrum.
After the exposure apparatus was assembled and the first test board was made, it was determined that an exposure time of between 15 to 20 seconds is all that was required to properly expose the board. There have been several other projects out there where 5mm UV LEDs were used, but those resulted in exposure times which varied from several minutes to tens of minutes depending on the quality of the LEDs use. Needless to say, at 15 to 20 seconds, this solution has given them that rapid prototype ability. Read on for the build process and see the unit in operation.
Introduction – Design – Create Positive Image – Prepare The Board
Expose The Board – Develop Board – Etching – Thoughts