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SOLDER FOR WAVE SOLDERING

SOLDER FOR WAVE SOLDERING. The Standard Alloy: 63% Tin/37% Lead Pure Metals Melt (go from a solid to a liquid or from a liquid to a solid) at One Temperature

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SOLDER FOR WAVE SOLDERING

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  1. SOLDER FOR WAVE SOLDERING • The Standard Alloy: 63% Tin/37% Lead • Pure Metals Melt (go from a solid to a liquid or from a liquid to a solid) at One Temperature • Mixtures of Metals (alloys) Usually Melt Over A Range of Temperatures (solid and liquid exist over a range of temperatures - this is called a mushy zone or a pasty range)

  2. SOLDER FOR WAVE SOLDERING • A EUTECTIC is a special alloy composition where melting occurs at a single temperature. • 63% Tin and 37% Lead is the eutectic composition for the Tin-Lead System of Alloys Melting Temperatures = 183oC or 361oF

  3. GRADES OF SOLDER • Level of Metallic Impurities - Metallic Impurities Can: • Cause severe bridging defects (particularly when iron exceeds 0.005%) • Weaken solder joint strength • Increase Dross Rate • Cause dull or grainy solder joints • Reduce the wetability (particularly sulfur) Compare Supplier's Specifications

  4. GRADES OF SOLDER • Level of Non-Metallic Impurities or Included Oxides • Included oxides wet very well to molten solder and do not easily separate from the solder into the dross • Included oxides increase the viscosity of molten solder, which makes the solder more sluggish, causing bridging and icicles • Included oxides can be measured via the Dross Inclusion Test

  5. PURPOSE OF FLUX • Reduces oxides on all surfaces involved in the solder connection • Reduces surface tension of molten solder • Helps prevent reoxidation of surfaces during reflow • Assists in transfer of heat to solderable surfaces

  6. TYPES OF ASSEMBLY FLUXES • R- ROSIN (no halides/no organic acids) • Suitable for no-clean or solvent/saponifier cleaning • RMA- ROSIN, MIDLY ACTIVATED (limited halides/limited weak organic acids) • Suitable for no-clean or solvent/saponifier cleaning

  7. TYPES OF ASSEMBLY FLUXES • RA- ROSIN, FULLY ACTIVATED (halides/weak organic acids) • Used by some for no-clean; usually cleaned with solvent/saponifier • RSA- ROSIN, SUPER ACTIVATED (high level of halides and weak organic acids) • Clean with solvent/saponifier

  8. TYPES OF ASSEMBLY FLUXES • OA- ORGANIC ACTIVATED (high halides, high level of strong organic acids) • Must clean with water or saponifier • NO-CLEAN - Uncleaned residues do not degrade Surface Insulation Resistance • ROSIN-BASED - Rosin/Resin with weak organic acids and halides • ROSIN/RESIN-BASED - Weak organic acids • VOC-FREE - Usually rosin/resin-free; weak organic acids. Alcohol is replaced by water. • ROSIN/RESIN-BASED - Weak organic acids only (no halides)

  9. Weak Organic Acids RMA, RA, RSA, No-Clean Strong Organic Acids OA Amines RMA, RA, RSA, OA, No-Clean Rosin/Resin R, RMA, RA, RSA, No-Clean Halides RMA, RA, RSA, OA, Rosin-Based No-Cleans FLUX COMPONENTS ACTIVATORS

  10. VEHICLES Glycols OA Polyglycols RA, OA Surfactants OA, No-Cleans SOLVENTS Alcohols Glycol Ethers Petroleum Water Various High Boiling Solvents FLUX COMPONENTS

  11. What are the Top 10 variables Influencing Solderability? 1. Solderability Of Boards (Pads/Holes) and Components 2. Spray Fluxer Capabilities - penetration of flux into holes - uniformity of flux deposition - day-to-day consistency 3. Flux Selection

  12. What are the Top 10 variables Influencing Solderability (cont.)? 4. Amount Of Flux Applied 5. Board Orientation 6. Conveyor Speed 7. Preheat Temperature 8. Use Of Chip Wave 9. Solder Pot Temperature 10. Inert Gas Wave Soldering

  13. PROCESS OPTIMIZATION • In the Wave Soldering Process, it seems like there are many variables which can affect soldering performance, how can I quickly and efficiently identify the optimal process settings? Answer: Designed Experiments

  14. PROCESS OPTIMIZATIONFractional Factorial - Four VariablesTwo Levels - Twenty Replicates

  15. PROCESS OPTIMIZATIONFractional Factorial - Four VariablesTwo Levels - Twenty Replicates

  16. Application Foam Wave Spray (sealed flux reservoir) Control Specific Gravity Titration None Flux Application Methods

  17. Advantages Low Capital Cost Copper Boards Disadvantages Flux Volume SG Control Foam / Wave Fluxing

  18. Advantages Even Deposition Volume Control Sealed Supply Minimum Flux Waste Disadvantages High Capital Cost Hole-Fill with Bare Copper Boards & OSP뭩 Spray Fluxing

  19. SPRAY FLUXERSWHAT SHOULD THEY BE ABLE TO DO? • Hold Flux in A Sealed Container • Why? No exposure of flux to air, therefore, no evaporative losses. No need to monitor the solids content of the flux. No need to add thinners. • Provide Ability to Adjust the Flux Deposition Precisely • Why? Amount of flux applied is an important variable to control to reduce defects. The precise control of the amount of flux applied will allow optimization of the process.

  20. SPRAY FLUXERSWHAT SHOULD THEY BE ABLE TO DO? • Provide Uniform Flux Deposition Across the Width and Along the Length of the Board • Why? Process control for defect minimization. • Is there a simple method that can tell me if my spray fluxer is applying a uniform coating of flux? A piece of cardboard!!! It is not high technology, but it will quickly tell you if you have a uniform spray pattern. • Easy to operate, maintain, and does not clog easily.

  21. SPRAY FLUXERSWHAT SHOULD THEY BE ABLE TO DO? • Good Hole Penetration for Topside Hole-Fill • I heard that by heating a VOC-Free flux before spraying it, you can achieve much better capillary action of flux up the holes and achieve better hole-fill. Is this true? • No. When a fine mist of flux is sprayed, the air cools the flux almost immediately (even after heating to 185oF), providing no added benefit to hole-fill.

  22. SPRAY FLUXERSWHAT SHOULD THEY BE ABLE TO DO? • I know that it is important to apply the same amount of flux to every board, every day, but how can I tell if the spray fluxer is delivering the same amount of flux consistently? • THE IONOGRAPH!

  23. Solder Balls In Wave Soldering 3 Types: • 밪plash-Back?Solder Balls From Fully-Inerted And Tunnels • Random (밪pattering-Type? • Non-Random (found behind the protruding leads on the bottomside)

  24. Random Solder Balls Found randomly on topside or bottomside of board.Listen for associated 밪IZZLE?at wave. Common when using VOC-Free fluxes. • Check Preheat Profile (max. ramp rate to desired topside preheat and hold) • Forced Air Convection Preheat • 밮ented?Pallets Or Pallets With Finger-Like Bottom Edge Design

  25. Non-Random Solder Balls Found on the bottomside of board and observed at the same locations (board-after-board), usually at the trailing side of a protruding lead. Related to the surface tension between the solder mask and the solder. Primary Factors (60-90% reduction) • Mask Selection - Surface Morphology (matte much lower solderballs than glossy) • Mask Selection - Chemistry Of Mask • Flux Selection (Alcohol-Based: Lonco 65 Series; VOC-Free: NR310 Series)

  26. Non-Random Solder Balls Found on the bottomside of board and observed at the same locations (board-after-board), usually at the trailing side of a protruding lead. Related to the surface tension between the solder mask and the solder. Secondary Factors (20-50% reduction) • Amount Of Flux At Exit Of Wave - Amt of Flux Applied (more reduces solderballs) - Conveyor Speed (faster reduces solderballs) - Chip Wave (off reduces solderballs) Tertiary Factor (5-10% reduction) • Solder Pot Temperature (lower reduces solderballs)

  27. Non-Uniform Flux Application Solder Pot Temperature Too Low Conveyor speed too slow and flux is prematurely volatilizing due to excessive time in the wave Check spray pattern with cardboard and fix spray fluxer, if necessary If possible, increase solder pot temperature to 500oF. Increase Conveyor Speed by 0.5 - 1 Foot per minute TROUBLESHOOTING SOLDER BRIDGES/SHORTS Possible Cause Corrective Action

  28. Solder contamination with high levels of metallic impurities (particularly Iron > 0.005%) or high levels of included oxides Solder Wave Not Set-Up Properly Analyze composition of solder and perform dross inclusion test Make sure that the solder wave height reaches half thickness of the board and that other wave adjustments are set correctly TROUBLESHOOTING SOLDER BRIDGES/SHORTS Possible Cause Corrective Action

  29. Flux Chemistry is not optimized Rough Solder Wave Check the acid number of the flux to ensure that the flux is at the proper solids content and ask flux supplier for improved formulation to reduce bridging (Lonco 65 or NR310) Clear Wave Nozzles and Screen, Remove Dross TROUBLESHOOTING SOLDER BRIDGES/SHORTS Possible Cause Corrective Action

  30. Chip Wave Being Used Preheat temperature not set correctly If you don't need to use chip wave for soldering bottomside SMD's, do not use it. High preheat temp can prematurely volatilize the flux activators. Low preheat temperatures may not sufficiently activate the flux activators, then higher preheat temperatures may be required. TROUBLESHOOTING SOLDER BRIDGES/SHORTS Possible Cause Corrective Action

  31. Board Not Meeting Wave Parallel Leads Too Long Bridge only across last two leads of a row of leads (SOIC) Check for bent fingers/fixtures, non-level conveyor rails, wave/nozzles not level, conveyor width too tight Cut the leads to shorten them Add "Solder Thieves" into the design of the board TROUBLESHOOTING SOLDER BRIDGES/SHORTS Possible Cause Corrective Action

  32. Bridge only across last two leads (QFP) Improper Board Orientation Turn part 45o and add"Solder Thief" If possible, process boards in parallel direction with rows of leads. Run experiment to determine optimal direction. If possible, change design of the board so that board can be run parallel with the connectors. TROUBLESHOOTING SOLDER BRIDGES/SHORTS Possible Cause Corrective Action

  33. SOLDER SKIPS • Flux not properly applied to pad surface • Solder did not adequately contact pad surface • Flux does not posses sufficient wetting force or wetting speed for specific surface

  34. SOLDER SKIPS Was Flux Properly Applied? • Check spray pattern with glass plate or cardboard • Experiment with varying levels of flux application

  35. SOLDER SKIPS Did the Solder Adequately Contact the Pad? • Is the board contacting the wave uniformly and level? • Conveyor rails level? • Conveyor fingers bent? • Pallets/Fixtures bent or damaged? • Boards warped? • Solder pot level? • Conveyor width too narrow?

  36. SOLDER SKIPS Did the Solder Adequately Contact the Pad? • Is there solder mask on the pads? • Is there SMD adhesive on the pads? • Is the turbulent wave turned on? • Is the turbulent wave nozzle clogged? • Is the turbulent wave set too low? • Is the solder wave set high enough? (It should be ?up board thickness)

  37. SOLDER SKIPS Did the Solder Adequately Contact the Pad? • Can changing the orientation of the circuit board help (try 90o, 180o and 270o) • Pads too small or pads too far under part

  38. SOLDER SKIPS Flux Does Not Possess Sufficient Wetting For Surfaces? • Is there sufficient contact time in the wave (try reducing the conveyor speed)? • Are the pads and leads solderable? • Does the flux have sufficient wetting force/speed? • Make sure the acid number of the flux is correct • Ask flux supplier for an alternative flux (NR310H and Lonco 65H).

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