Pcb 101

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This is a presentation that I put together that explains the basic manufacturing process for printed circuit boards. There are many different ways to build a board. This presentation explains the basics of the most common operations. This is a general overview. For more information on the subject visit www.pcbdesignschool.com

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Pcb 101

  1. 1. PCB 101The Basics of Building a Printed Circuit Board. Presented by David Duross Engineering Director
  2. 2. Inner Layer Process.● Starts with copper clad FR4.● FR4 is a composite material of woven E- glass and epoxy resin.● Referred to as a core or C-stage.
  3. 3. Dry Film Lamination● Core is chemically cleaned to remove process residue or contaminates.● Core is laminated with Dry Film Photo-resist.● Cleaning operation promotes dry film bond to copper surface.
  4. 4. Dry Film Laminating Equipment● The dry film is laminated onto the core by use of a cut sheet vacuum laminator.● Conveyorized processing allows any thickness material to be laminated.
  5. 5. Dry Film Expose● Artwork is placed against the dry film.● The surface is exposed to high energy UV light.● The circuit pattern is exposed to UV light.
  6. 6. Exposure Equipment● Automated equipment allows a hands free operation.● System automatically aligns artwork front to back for accurate registration.● Interior of unit has hepa air filtration.
  7. 7. Dry Film Develop● The exposed dry film is chemically developed and made permanent.● Undeveloped dry film is rinsed away.● The dry film forms the circuitry pattern.
  8. 8. Copper Etch● The copper we dont want to keep is chemically etched away.● The dry film acts as an etch resist protecting the copper we want to keep.
  9. 9. Dry Film Strip● The dry film photo- resist is chemically removed.● The inner layer circuitry pattern is now formed.
  10. 10. Post Etch Punch and AOI● Post etch punch automatically adds mechanical alignment positions to the core in the form of four slots.● Provides accurate alignment for multiple cores.● Panels are then inspected on a system known as an AOI.● AOI is short for Automatic Optical Inspection.
  11. 11. Oxide Treatment● Copper is a very smooth surface.● The copper surface needs to be roughened up to promote bonding to epoxy resin later on. Oxide treatment does this.● FR4 after copper etch is rough enough to provide a good bonding surface.
  12. 12. Multilayer Lamination● The core forms the inner layers.● Sheets of pre-preg (B- stage) are placed against the core.● Copper foil is then placed against the pre-preg.● The copper foil forms the outer layers of the printed circuit board.
  13. 13. Lamination Press Equipment● Vacuum lamination systems evacuate air from the system under light pressure.● When the temperature increases beyond a control point the system applies high pressure.● Press cycles are controlled by a computerized system.● Multiple process panels are pressed at the same time in what is referred to as a lamination book.
  14. 14. Multilayer Lamination● The core, pre-preg and copper foil are pressed together under a vacuum with high pressure and heat.● The pre-preg liquefies, flows and encapsulates the oxide treated copper.● The pre-preg solidifies as temperature increases.● The stack is then allowed to cool.
  15. 15. Primary Drill● Holes are drilled into the pressed panel intersecting copper features on the inner layers.● Drilled holes are non-conductive.● Copper burrs at the edge of the hole are mechanically removed.● Drilling leaves an epoxy smear over the inner layer copper exposed by the drilling process.● The epoxy smear is chemically removed to ensure that the inner layer copper is exposed.● Note the location of the two holes.
  16. 16. Hole Formation● Drilling is done on an automated CNC drilling system.● De-smear is either done with a plasma etch system or with a chemical process line.
  17. 17. Copper Deposition / Direct Metalization● Copper deposition or direct metalization is applied to non-copper surfaces.● Material applied is very thin but conductive.● The conductive material provides the electrical pathway for electroplated copper later on.
  18. 18. Copper DepositionDirect Metalization● Direct metalization coats only the epoxy and glass.● Copper deposition coats everything.● Both can be processed vertically or horizontally.
  19. 19. Outer Layer Dry Film Lamination● Panel is chemically cleaned to remove process residue or contaminates.● Panel is laminated with Dry Film Photo-resist.● Cleaning operation promotes dry film bond to copper surface.● Cleaning is typically done prior to the copper deposition / direct metalization process.
  20. 20. Outer Layer Dry Film Expose● Artwork is placed against the dry film.● The surface is exposed to high energy UV light.● The circuit pattern is prevented from being exposed to UV light.
  21. 21. Outer Layer Dry Film Develop● The exposed dry film is chemically developed and made permanent.● Undeveloped dry film is rinsed away.● Openings in the dry film form the circuitry pattern.● Note that one of our two drilled holes is covered by the dry film.
  22. 22. Copper Plate● The dry film acts as a plating resist.● The dry film covers copper we dont want to keep.● Additional copper is electro-plated onto exposed surfaces not covered by the dry film.● Copper is plated in the hole not covered by dry film.● Approximately .001” (0.0254 mm) of continuous copper is plated in the hole.
  23. 23. Tin Plate● Electro-plated tin is plated directly onto the electro- plated copper.● The tin also plates into holes not covered by dry film.● The tin protects the copper we want to keep.● The plated tin is very thin.
  24. 24. Outer Layer Dry Film Strip● The dry film is chemically stripped away from the panel.● Note that the hole in the center of our sample is tin plated.● The hole on the right side is not plated with tin.
  25. 25. Copper Etch● The tin acts as an etch resist.● Copper not plated with tin is chemically etched away.● The hole plated with tin is protected.● The hole on the right was not copper or tin plated due to the dry film that covered it.● The copper deposition / direct metalization in the hole on the right is removed in the copper etching process.
  26. 26. Tin Strip● The thin layer of electro- plated tin is chemically removed.● The tin is also removed from the center hole.● All exposed electrical conductors are now bare copper.
  27. 27. Photo Image-able Solder Mask Application● A thin layer of liquid photo image-able solder mask is applied to all exposed surfaces.● The mask may be applied either by spraying or with a screen/squeegee.● The mask is a thin polymer coating roughly .004” (0.102mm) thick when wet.● The mask is tack dried for handling purposes.
  28. 28. Mask Expose, Develop and Cure● Artwork is placed against the tack dried solder mask ink.● Solder mask not covered by an artwork image is exposed to high energy UV light.● Exposed mask is chemically developed and made permanent.● Unexposed mask is washed away.● The solder mask is then thermally cured.● Cured mask shall be approximately .001” (0.0254mm) thick.
  29. 29. Hot Air Solder Leveling● Panels are coated with solder flux.● For vertical processing panels are dipped into a large solder pot.● For horizontal processing panels are passed through a solder fountain.● Excess solder is shaved off of the process panel with hot blowing air knives.● Solder is typically 200 micro-inches in thickness minimum.● Solder-ability is the acceptance criteria.
  30. 30. Component Markings● Component markings are applied with non-conductive inks.● Markings can be any color. White is the most common.● Inks can be applied by a screen/squeegee set-up or with an ink-jet printer.● Markings typically indicate component placement and orientation.
  31. 31. Marking Equipment● Ink jet printing applies a white epoxy ink sprayed as a final image and UV tack dried as the ink is applied.● Silkscreening relies on pulling a squeegee across a mesh. Openings in the mesh match the marking features.● Both techniques require the ink to be baked to ensure final cure.● UV cure-able inks are available as well.
  32. 32. Final Fabrication● Individual boards are routed and or scored free from the process panel.● Specialty milling such as counter bores and sinks may be added at this step.● Boards are rinsed free of process debris and dried.
  33. 33. Electrical Test● Boards are electrically tested for opens and shorts.● Testing is done on a dedicated fixture or with a robotic system referred to as a flying probe tester.
  34. 34. Final Inspection● Boards are visually inspected to either customer requirements or industry standards.● Boards are measured for dimensional accuracy.● Boards are tested for ionic contamination.
  35. 35. End

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