[ Pobierz całość w formacie PDF ]
.Boards also differ in the type of base material they aremade of.This fuel cell requires the FR-4 glass epoxy resin base, clad withcopper on one side only.We used a 1 ounce, which is coated with copperto a thickness of.0014".The FR-4 was chosen because it is very stiff, which is necessary for thisdesign.It is important for the electrode grid structure to be as stiff as pos-sible so that it maintains an even contact surface over the membrane sur-faces within the assembly, especially when it is tightened with the pres-198sure adjustment screws.Planar Fuel Cell StackYou can experiment with other types of copper clad board with differentbase compositions, just remember that stiffness and machinability are thekey concerns.Preparing the electrodes for template transferThe first step in fabricating the PC board electrodes is to clean eachboard thoroughly.You can use a Scotch Brite® pad and water to clean thecircuit board.Even though the circuit board looks shiny and very clean,rub it all over with the pad and then rinse with water.After you clean the board, be sure not to touch the copper surface withyour fingers as this will leave minute traces of oils and dirt that can inter-fere with the processes of image transfer, plating, and the electrical per-formance of the surface.A good habit for working with copper clad is towear clean thin cotton gloves to protect the surface of the board while youhandle it.Dry the surface of the board with a lint free cloth.Inspect the edges ofthe circuit board for burrs.If there are any, file them off.The idea is to geta clean smooth surface, so that the transfer film that will lie flat on thecopper surface.Be sure that after you clean and wash the board that noresidue is left on the surface.199Planar Fuel Cell StackTransferring the templatesThe templates for the oxygen and hydrogen flow fields/electrodes in thisbook (see page 248) are intended to be printed on plastic transfer film andthen transferred to copper circuit board for etching.This method is com-monly used to transfer printed circuit board designs to the copper surfaceof the boards.We used Press-n-Peel®, which is a plastic film that has anemulsion on one side and comes in sheets of 81/ 2"x 11" size.The plasticsheet is loaded into the printer just as any other 81/ 2"x 11" paper would be.Use a laser printer to print the templates for the two circuit boards on thefilm.Print the image on the dull (emulsion) side of the transfer film.If youdo not have a laser printer, you can print out a paper copy on whatevertype of printer you have and then get a laser copy at a copy shop.If you use a laser printer, do not let it warm up before printing.Print thetemplate to the transfer paper immediately after turning on the laser print-er.The reason is that the heat from a laser printer will affect the surface ofthe transfer film and can produce defects in the image.It is important toget a very sharp, clean, well covered, distinct image, as the transfer filmwill pick up the slightest imperfections.200Planar Fuel Cell StackThere are two circuit board templates, the oxy-gen side template, and the hydrogen side tem-plate.When you have finished printing your tem-plates on the transfer film, lay the film emulsionside down on the copper surface of each of thecircuit boards.Above, the oxygen elec-For Press-n-Peel®, heat from a clothes iron istrode template printedapplied to transfer the template to the copper.Theon transfer film.Below,lay the film emulsionsuggested starting temperature is 275° to 325° F,side down on the circuitwhich is usually the acrylic and polyester setting.board, and secure theNot all irons are the same, and you may have tofilm to the circuit board.experiment a little to get the right heat.I found thatusing the higher "linen"setting worked better forthese large sized boards.You can attach thetransfer film to the boardwith some adhesive dotsas I did to hold the filmin place on the edges201when you start to iron.Planar Fuel Cell StackPlace a piece of paper between the iron andthe transfer film to help the iron glide betterover the surface.Move the iron very slowlyover the surface area of the whole board mak-ing sure to not miss the edges.After about ten minutes of slowly movingUse a piece of paperthe iron around on the surface, lift a bit of thebetween the iron andfilm up from the surface of the copper cladthe transfer filmand see if the image sticks to the surface ofthe copper.If it is not sticking, or parts are missing, iron over those par-ticular parts or go over the surface again slowly until the whole image istransferred.Keep checking the progress of the transfer by gently peeling the filmfrom the copper surface every once and a while to see if the image istotally and satisfactorily transferred.Please note that there must not be any continuity breaks in the coppersurface.This does not mean no blemishes or imperfections, but doesmean that if you put a multimeter probe on one side of a copper tracethere should be a continuity beep when the probe is placed on the otherside of the copper trace.Take your time with this step.Keep ironing until202Planar Fuel Cell Stackall of the transfer is complete.This can be atedious operation but it is a very important todo it well.When the ironing is completed to your sat-isfaction, take the circuit board and transfersheet, and run it under cold water.After it hasWhen ironing is complete,cooled down, slowly peel the transfer sheet peel back the transfer film.off [ Pobierz caÅ‚ość w formacie PDF ]