Smt basics


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Smt basics

  1. 1. Surface Mount Manufacturing BasicsFamiliarization information for SMT printed circuit boardproductionJuly 9, 2012
  2. 2. SMT Production Processes 1. Screen Printing 2. Adhesives/Epoxy Dispensing (Optional) 3. Pick and Place 4. Reflow 5. Inspection Post-Reflow (Optional) 6. Secondary PCB assembly (Optional) 7. Cleaning (Optional) 8. Depaneling 9. Product Sub Assembly / Product Assembly 10. Testing 11. Packaging 12. Shippingpage 2 / July 9, 2012
  3. 3. Processes Defined • Step #1 Screen Printing – A bare PCB with all of the pads for surface mount components is placed into a screen printer where solder, in a paste form, is forced through a screen (with artwork to match the PCB) and onto the pads of the 3 / July 9, 2012
  4. 4. Processes Defined • Step #2 Adhesives / Epoxy Dispensing (Optional) – A PCB with solder paste on the pads has adhesive or epoxy dispensed onto select locations. – This is typically only used when components are known to move prior to reflow (MELFS) or more commonly used to hold components prior to and during wave 4 / July 9, 2012
  5. 5. Processes Defined • Step #3 Pick and Place – The PCB with the solder paste on the pads is presented to a pick and place machine. This machine picks up, inspects, and places components onto the solder 5 / July 9, 2012
  6. 6. Processes Defined • Step #4 Reflow The result when the paste cools The PCB with components as the PCB exits the oven is a basically on top of solder paste mechanical and an electrical enters the oven and is gradually bond between the component(s) introduced to temperatures that and the PCB. cause the solder paste to become liquidous, once the paste is liquidous, the parts settle into the paste and make electrical contact with the SMT 6 / July 9, 2012
  7. 7. Processes Defined • Step #5 Inspection (Optional) – The inspection or AOI (Automated Optical Inspection) can be performed pre or post reflow. This is typically an automated machine that uses a camera and verifies correct component placement and rotation. – Pre-reflow inspection allows for easier rework if neededpage 7 / July 9, 2012
  8. 8. Processes Defined • Step #6 Secondary Manufacturing / Insertion – The SMT assembled PCB May have pins, tabs, connectors or other press fit type items installed. – This step is application dependant and may happen pre or post inspection, dependant upon the final product and custom application specificationspage 8 / July 9, 2012
  9. 9. Processes Defined • Step #7 Cleaning (Optional) – The assembled PCB is run through an aqueous cleaning unit to ensure no contaminents or flux reside is left on the PCB. – This step is optional because a “no-clean” solder may be used whereas no cleaning is necessary, many customers clean PCB’s regardless of the type of solder and flux usedpage 9 / July 9, 2012
  10. 10. Processes Defined • Step #8 Depaneling – Individual images are depaneled or separated from the multi-up array by various means including hand separation, breaking, routing, or punching. – This step is very often overlooked even though the PCB is complete and very expensive at this point in the manufacturing 10 / July 9, 2012
  11. 11. Processes Defined • Step #9 Product Subassembly / Assembly – The assembled, depaneled PCB is placed into a housing or made part of the larger assembly being built by the manufacturer – This step is different depending upon the product(s) being manufacturedpage 11 / July 9, 2012
  12. 12. Processes Defined • Step #10 Testing – The final product is tested • Step #11 Packaging – The final product is packaged for shipment • Step #12 Shipping – The final product is shipped to the end user, distributor, or customerpage 12 / July 9, 2012
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