Prologue to Surface Mount Innovation 24 April 2002 Helen Holder.


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Prologue to Surface Mount Technology 24 April 2002 Helen Holder What is surface mount? Printed circuit sheets Surface mount segments Assembly & Rework Questions Topics A method for joining electronic parts to a printed circuit board
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Prologue to Surface Mount Technology 24 April 2002 Helen Holder filename\location

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What is surface mount? Printed circuit sheets Surface mount parts Assembly & Rework Questions Topics filename\location

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A method for appending electronic segments to a printed circuit board The weld joint structures the mechanical and electrical association Bonding of the patch joint is to the surface of a conductive area design Connection does not use through openings or terminals What is "surface mount"? filename\location

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Surface Mount versus Through Hole Surface Mount Through Hole filename\location

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littler parts denser design less expensive pcbs (no openings to penetrate) enhanced stun and vibration attributes enhanced recurrence reaction simpler to shield from EMI/RFI less demanding to computerize fabricating Advantages of SMT filename\location

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more warmth created little freedom makes cleaning troublesome visual assessment troublesome great joint arrangement essential for mechanical dependability of get together harder to hand gather more prominent number of various materials to match CTE\'s Disadvantages of SMT filename\location

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What is surface mount? Printed circuit sheets Surface mount parts Assembly & Rework Questions Topics filename\location

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Most regularly experienced sorts of substrates: Laminates (FR-4, and so forth.) Ceramics Flex For more data, see High Performance Printed Circuit Boards by Harper (McGraw-Hill) Printed Circuit Boards (PCBs) filename\location

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FR-4 is the most generally utilized material since it\'s sufficient for most applications and shabby When not to utilize FR-4: High unwavering quality and/or hot segments: high T g , like FR-405, or significantly higher temp with artistic High recurrence: low dielectric misfortune (tan d, for example, PTFE (Teflon) High speed computerized lower dielectric constants (e r ), polyimide or PTFE Form elements: flex can turn corners Need CTE match to chip: fired FR-4 filename\location

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Some PCB Laminate Materials filename\location

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Make (purchase) FR4 overlay center Pattern Cu Laminate (press and warmth) Drill Plate Cu Route pictures Test How to make PCBs filename\location

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How Laminates are Made Prepreg: semicured material that is dry and nontacky. It can be put away. Impregnate glass with epoxy gum Dry/Cure Roll of woven glass Cut Press Prepreg Copper Foil FR4 center cover filename\location

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How PCBs are Made FR4 overlay center Pattern Cu Layer with prepreg and cover (press and warmth) Drill (plate external layer and openings) Pattern external layer (Route pictures & test) filename\location

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Use a format system to do plan, segment position, and impression definition: Cadence\'s Allegro or Orcad Pads/Innoveda\'s PowerPCB Mentor\'s Board Station MicroCAD\'s Qcad, and so forth. SMT Layout filename\location

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Design libraries are accessible for most parts New impressions can be included physically Often impressions can be downloaded from the part seller or from Topline ( http://www.toplinedummy.com ) There are IPC plan rules (IPC-SM-782 at http://www.ipc.org ) and Jedec segment definitions ( http://www.jedec.org ) In models, you\'re most worried with fitting the part on the board appropriately, however in genuine items we consider joint geometry for assembling yield and item dependability. (impression = cushion measurements and area designs) Footprints filename\location

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How to Specify PCBs This is the data you ought to give when requesting PCBs: Quantity and lead time X-Y measurements/loads up per board, number of sides with segments Board material, thickness (4 layer loads up typically 0.062") and resiliences Layer check and copper weight for layers: ½ oz or 1oz copper on external layers (less copper implies shorter engraving times) 1 oz copper on inward layers (convey more present for ground/power planes) Metallization (SnPb/HASL, natural, Cu-Ni-Au, inundation Sn or Ag or Au) Minimum line and space width (< 0.008" costs more) Hole tally, min gap diminish and complete (openings < 0.015" cost more) Surface mount cushion tally and least cushion pitch Silkscreen and weld veil (generally green LPI) Electrical testing necessities (need netlist for electrical test) Gerber information (dependably make a README document) filename\location

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Where to have PCBs made There are huge organizations like Multek and Hitachi, yet you most likely won\'t utilize them in light of the fact that your volumes are too little. You\'ll presumably utilize organizations like: Sierra Proto Express http://www.protoexpress.com Proto Engineering http://www.protoengineering.com Some individuals that have been exceptionally useful in the past are: Dene Winstead dene@finelinecircuits.com Donna Havisto dhavisto@cir-tech.com Sanjay Agarwal Sanjay@cirexx.com Paula Gupta paula.gupta@aadec.com You can have numerous, numerous sellers cite your board at http://www.pcbmarketplace.com/Printed Circuit Design magazine has a purchasers guide that can be useful: http://www.pcdmag.com filename\location

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What is surface mount? Printed circuit sheets Surface mount segments Assembly & Rework Questions Topics filename\location

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chip resistors, capacitors little blueprint transistors (SOT) PLCC (J lead) Common SMT segments May not be accessible as surface mount: Some connectors Transformers/solenoids Large electrolytic tops QFP, SOIC, TSOP (gull wing) territory exhibit (BGA, CSP, flip chip) filename\location

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Ordering SMT Components For little quantities of parts (model amounts), use segment wholesalers, for example, Digi-Key http://www.digikey.com Newark http://www.newark.com Keytronics http://www.keytronics.com Avnet http://www.avnet.com Jameco http://www.jameco.com EDX http://www.edxelectronics.com Etc., and so on., and so forth. Internet requesting is simple. Glance around at great costs. filename\location

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Specifying SMT Components are generally requested by part number. Ensure you have the right: Functional specs and resistances Package sort (QFP, TSOP, and so forth.) Lead sort (gull wing, J-lead, and so on.) X-Y measurements (e.g. TSOPs can have the same number of pins yet diverse body lengths and widths) Pins/pin outs/impression Bulk bundling (tape & reel, tubes, plate) Quantity for the part number you ask for . Requesting more is less expensive per part, yet don\'t arrange parts you won\'t utilize. filename\location

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What is surface mount? Printed circuit sheets Surface mount segments Assembly & Rework Questions Topics filename\location

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Surface mount get together process steps: Solder glue printing or apportioning Component arrangement Reflow Inspection Rework/backload Cleaning A decent reference: Surface Mount Technology by Prasad (ITP) Assembly filename\location

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Solder glue has modest metal circles of the combination blended with flux, solvents, and thixotropic materials Methods of applying weld glue: Stencil printing Syringe administering Most powerful step influencing yield Paste and printing filename\location

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Reflow Once parts have been set on the patch glue blocks, the whole board is set in a broiler and taken through a temperature profile like: filename\location

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Look for wrong/lost segments and poor bind joints Fix issues and include parts that can\'t survive the high temperature of the reflow stove Wash to expel flux deposits Inspection/Test Rework/Backload Cleaning filename\location

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If you\'re sufficiently fortunate to have a little spending plan for get together, you may have the capacity to have a proto shop manufacture your sheets. Some spots to look: Naprotek ( http://www.naprotek.com ) Jabil ( http://www.jabil.com ) Analog Technologies ( http://www.analog-tech.com ) Having another person do the gathering filename\location

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Use vast segments/huge pitch Dispense (generally SnPb weld glue) Use a powerful glue with a wide process window Alpha WS609(if you can clean the board or couldn\'t care less about long haul unwavering quality) Kester R244 in the event that you can\'t clean Hand place segments with tweezers don\'t give glue a chance to dry out don\'t push down too hard dependably utilize ESD security Hot plate just should be liquid (~200C) for 60-90s Clean, if essential Doing it yourself filename\location

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Defects happen in the best assembling process: Wrong part Reversed extremity Misaligned part Shorts/spanning/overabundance bind Opens/deficient patch Nonwetting/unreflowed patch Rework and hand fastening unreflowed bind glue filename\location

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Remove segment Clean cushions Re-tin cushions Install new segment Rework filename\location

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Applying flux to all area/leaded ranges Position the spout over part Turn on vacuum and set vacuum glass on part Lower spout and liquefy all joints Lift segment Removing Components (utilizing hot air patch framework) filename\location

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Apply flux to grounds Lay plait on patch to be evacuated Place iron tip on interlace, and when bind stream stops, expel twist and tip Remove Old Solder (with cutting edge tip on fastening iron) filename\location

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Apply flux to terrains Tin the edge tip Place the sharp edge delicately along the inside line of the column of grounds Gently draw the tip off the terrains after the weld liquefies Re-tin and Level Pads (with edge tip on patching iron) filename\location

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Dispense bind glue in a long, single line over cushions Place segment Adjust gaseous tension Dry glue until it seems dull Move tip closer and warmth until patch dissolves Clean, if important Install New Component (utilizing hot air pencil) filename\location

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Apply flux to the crossed over leads Clean tip of patching iron Hold the tip so it runs parallel to the line of leads Bring the level surface of the tip down on the scaffold and sit tight for reflow Draw the extension tenderly down far from the segment Fixing Shorts filename\location .:tslidesep.

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