Vapor phase technology 2011


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Vapor phase technology 2011

  1. 1. Presentation Overview Basics of Lead Free VP reflow Vapor Phase History Vapor Phase Explained Reflow Soldering Development Challenges and Solutions Convection versus Vapor Phase Vapor Phase Profiling Vapor Phase Samples Conclusions Questions 1
  2. 2. Basics of Lead Free VP reflow• Understanding Reflow Variation – Peak temp  Planning a Lead Free reflow profile requires understanding variation in the component material and process:  Lead free BGA’s can be shipped with many different alloy types  Most common are SAC305 and SAC105.  It has been found that BGA’s changing from SAC105 to SN100 and suspected pure tin.  Why?  Because the cost of Silver is increasing, and to remove silver lowers the cost to produce  Packaging suppliers are doing this without advising manufacturers.  We need to develop reflow for the worst case scenario: Pure Tin Balls  It is very important to study and understand the variation of the reflow system from load to load.  Typical in industry is to ensure that peak temperature is at 15 degrees above melt temperature of the solder.  Since we are dealing with a solder bump on the BGA – We also need to consider its melting temperature 2
  3. 3. Basics of Lead Free VP reflow• What Time/Temp do we need? First off – We need to generate soldering reflowprofiles using a thermocouple probe through the middleof the BGA devices into the balls. Second – We need to make sure that our solderreflow peak temperature PT is above 232 C according tothe BGA bumps solder chemistry, and then also consider the variation of the Oven and the reflow profile.  The worst case scenario should be a PT=240 C Third – We have to ensure that our solder time above 240 C is maintained at least 30 seconds for good soldering, but the time above 217 C must not be longer than 150 Seconds per J-STD-020D 3
  4. 4. Basics of Lead Free VP reflow• But how Hot is Too Hot?  J-STD-020D advises the peak temperature (PT) of devices for Lead free reflow is:  245 C for large plastic components, and  260 C for smaller plastic components  SO – If we stay under 245 C, then we don’t need to review of the component manufacturers specifications  BUT – If we go over 245 C, then we need to pull spec sheets on all parts to ensure we are not exceeding temperatures. 4
  5. 5. Basics of Lead Free VP reflow• Why is Vapor Phase technology an advantage?  In the Vapor Phase – the peak temp (PT) is set by the fluid boiling temperature point.  The fluid and the generated vapor temperature is always between 240 C and 245 C  We can be assured the parts are within J-STD 020D ! 5
  6. 6. Vapor Phase History Developed in the early 70’s, patented by Robert Christian Pfahl and Hans Hugo Ammann of Western Electric and Bell Labs. Used in high quality Military as well as Aerospace programs. Heat is transferred when the hot, saturated vapor condenses on a surface and gives up its latent heat of vaporization. The fluid boiling point is the governing factor in peak temperature.Patented Vapor Phase (by Two layer vapor phasePfahl and Ammann) (by Tze Yao Chu et al.) Combination of Reflow Soldering and Wave Soldering in a Vapor Phase (by W. Scheel et al.) 6
  7. 7. Vapor Phase Explained The vapor encapsulates the entire surface of the board, resulting in smallest ΔT at very short dwell times of the board in the condensing vapor (thermal equilibrium) The heat transfer coefficients are roughly ten times greater than the values that are reached through radiation or convection. 7
  8. 8. Reflow Soldering DevelopmentΔT~50ºC ΔT~20ºC ΔT~2ºCPAST PRESENT FUTURE 8
  9. 9. Challenges and SolutionsPast Vapor Phase technology : Today most of the challenges were addressed :  Environmentally-friendly Environmental concerns of the fluids being used.  CFC free, non-flammable, and non- toxic. Lack of fluid selection (few boiling  Blood replacement substance. temperatures).  ION Chromatography and Surface Insulation Test (SIR) showed no residual An inherent problem with tombstoning and contaminates on the PCB post-reflow. voiding.  Thermally and chemically stable (inert gas Limited automation capability. atmosphere)  Perfluorinated fluids have a viscosity Throughput limitations (PCBAs exposed double than H2O ( high molecular weight) to the vapor process longer than the tact  Colorless and electrically non conductive. time of the placement processes).  Large variety of boiling points selection…PEAK TEMP: In-line batch carrier machines were more  200, 215, 225, 230, 235, 240, 260 C mechanical, and prone to more maintenance. 9
  10. 10. Challenges and Solutions No more vapor phase related tombstoningThe main driving force controlling tombstones is the relative speed of the solders wettingaction (ramp rate) at the each end of the component.Vapor phase soldering have variable gradient control so the appropriate dropping depth isdetermined for every product using patented SVP (Soft Vapor Phase) and SolderAutomaticresulting in a very accurate slope and reduced tombstones failures. 10
  11. 11. Challenges and Solutions Integration of a local vacuum chamber reduces void presence  Gases and flux residues are draw off from the joint, as long as the solder is molten  Results in a more robust solder joint. 11
  12. 12. Challenges and Solutions Fully automatic due to patented Soldering-Automatic and SVP PLC control. Vapor phase efficiency improved when changing from product A to product B and completed faster thanthe time taken up by the up-stream pick`n`place processes ( high throughput ≤ 15 up to 20seconds/panel). Can produce double sided SMT PCB’s at rates comparable to in line convection and IR reflow processes (max. board size 800 X 650 X 80 mm). Superior solder joint appearance. In-Line Batch carrier VP systems are capable of processing product Bboard size changes while product A is still being soldered. PCB size adjustments can be completed, andwith IR pre-heat followed by VP soldering, there is no delay to change over once the sizing is completed. Maintenance requirements for cleaning the system is minimized, flux residues are extracted on thecompletion of each cycle. 12
  13. 13. Challenges and Solutions Vapor Phase maintains a low temperature on the BGA lid (made of a heat/moisturesensitive plastic). High convection temperatures causes the lid to warp down in the corners, a major causeof bridging due to the use of poor BGA substrate materials. Some component manufacturers have not redeveloped their original lead-processingpackages for lead-free temperatures, but have simply balled them with lead-free solder, orthey are offering a less-expensive, transitional package as they move to lead-free. Vapor phase ensures that the difference in temperature ΔT between the solder balls isunder 2ºC. 13
  14. 14. Challenges and SolutionsConventional convection soldering machines Capable of delivering the heat required for the lead-free soldering process, but process results vary. The reflow zone changes are significant between the products. Increased changeover time. Larger soldering machines, along with increased necessity for protective gas add to the already high energy requirements. The process requires:  Additional energy  Protective gas  Larger machines Delivered results are:  A high risk of thermal damages  Increased number of cold solder joints  Significantly higher emissions 14
  15. 15. Challenges and SolutionsIn convection ovens soldering track is further increased to avoid solder cracks and enable a smooth overalltemperature ramp up Solder Crack in L-leaded package Solder Crack in J-leaded packageIn line vapor phase machines for high volume production : Nitrogen Cost Compact size (Length < 5 meters) Indirect Energy Cost Delivers an 100% protective gas atmosphere as Direct Energy Cost part of the soldering process without extra cost Conventional Reflow Vapour Phase Reflow Soldering Soldering 15
  16. 16. Challenges and SolutionsReduced Cost 1. WPC-Loading 5. WPC-Unloading 3. Vapor Phase 1/3 direct Energy consumption. Soldering 2. IR-Preheating 4. Cooling No compressed air required. Reduced heat up of work shop saving acclimatization cost. Higher temperature substrate material can add 10 to 15% to PCB cost. Standard FR-4 used as PCB laminate material rather than (higher cost) FR-406. Fast setup for new products (wide range of products are processed with identical setup). Delivers an 100% protective gas atmosphere as part of the soldering process without extra cost.Low/No emission Closed loop process prevents the vapor from escaping to the surrounding environment. 16
  17. 17. Challenges and SolutionsVapor phase : Overheating is physically impossible with proper fluid selection. No cold solder joints due to determined heat transfer and absence of shadowing. Best possible wetting due to fully inert environment. Thermal transfer is independent of form, color, mass and mass distribution of PCBAs. Fixed peak temperature and superior heat transfer on thermally challenged PCB’s. Superior thermal equilibrium offers processing advantages ( large mass connectors, electrolytic capacitors, non-sealed switches and sensor devices) 17
  18. 18. Challenges and Solutions Shadowing of lower side of BGA requires excessive temperature on top of BGA Unsoldered balls appear as a result from shadowing effects Vapor rises above and below the BGA. Heat transfer encapsulates the whole assembly No Shadowing 18
  19. 19. Challenges and SolutionsTin whiskers are small, thin metallic hair-like growths that naturally emerge from thesurface of solid tin (Sn). On lead-free tin surfaces, tin whiskers may grow to a lengthsufficient to short one electronic circuit to another, creating product failure. Tin melting point = 505.08K (231.93 C, 449.47 F)With a 235 C fluid the vapor phase will reflow components tin coatings at the lowestpossible temperatures. 19
  20. 20. Challenges and Solutions Backward and Forward compatibility  Lead-free components are introduced in lead-based processes  Termination changes require additional modification to solder profiles and flux chemistries to ensure proper wetting of the solder to the lead-free termination.  Nitrogen in convection reflow is becoming more a requirement than an option, and nitrogen is expensive.  Backward compatibility – the majority of components are tin/lead, but some are lead free.  Going with a higher reflow temperature for a few lead-free components will affect adversely the majority of tin/lead components.  Forward compatibility – most components are lead-free, but some are still tin/lead Using a lead-free profile may damage some of the tin/lead components Vapor Phase is being considered as a solution to provide a middle-of-the-road compromise reflow profile that dissolves the lead into the solder joint in a homogeneous mixture and offer a higher reliability end-product. 20
  21. 21. Challenges and Solutions Convection reflow due to Lead free variables like melting point (between 217 C and 227 C) and the peak reflow temperature (between 230 C - 260 C) can results in:  Affects reliability of via holes and the reliability of interconnections  The blue, green and red matte mask can peel off the board .  High thermal mass boards push the limits of convection reflow equipment  FR-4 substrate increased temperatures is causing thermal degradation or decomposition  Increased thermal expansion (CTE) compromise the structural integrity of the board ( Z-axis expansion of FR-4 is greater at lead-free).  PT is causing plated through via barrel cracking, board warpage, and delamination.  Phenolic lead-free laminates are used which increase board cost by 10-15%.  Higher glass transition temperature Tg>170ºC  Low coefficient of thermal expansion (CTE) – lower Z axis expansion before and after Tg In the Vapor Phase process standard FR-4 is used as PCB laminate material rather than (higher cost) FR-406 due to lower constant boiling temperature of the fluid. 21
  22. 22. Challenges and Solutions Vapor Phase reduces the intermetallic compound (IMC) thickness  As the IMC increases, the joint strength is reduced due to the brittle nature of the intermetallic.  It is recommended that SnNi IMC layers be within the range of 0.4 – 1.0 micro-meters and SnCu IMC layers should be targeted in the range of 0.8 – 2.5 micro-meters. The use of Vapor Phase Soldering for lead-free processes decreases the IMC thickness and the microstructureshows finer secondary phases for profiles with peak temperature of 235ºC Crack at PCB through IMC Layer IMC growth made the joint more brittle Intermetallic phase at a soldering time T=100s Thickness of the Cu- layer in µm Sn Soldering temperature in C 22
  23. 23. Challenges and Solutions Vapor Phase increases visual appearance of solder jointsFiner structuresLess OxidationBetter distribution due to increased wetting capabilities Soldered in Vapor Phase oven Soldered in Convection oven 23
  24. 24. Challenges and Solutions Solder Paste can be used after expiration date Paste within expiration date Paste after expiration date With inert gas convection reflow no good solder joints could be made only 4 weeks after expiration date of the paste. With Vapor Phase soldering good solder joints could be established even 21 weeks after expiration date. 24
  25. 25. Profiling Lean principals are applied to new product development.  New products are launched on production lines used in day to day operations.  Prototype lines are becoming harder to justify.  Matrix charts are developed on thermal mass, layer count, and complexity to get the profile close so the process development time is kept to a minimum.  VP reflow profiling can be classified by chemistry type, minimizing profiling time.  Advances in VP process systems allow machines to profile almost automatically.  Ramp rates and soak times at peak temperature can be defined by the engineer, and controlled by the systems regardless of the product mix during the process.  In a true one piece flow on a prototype, it is much easier to get it right the first time using VP processing.  The days of inadequate reflow temperature or over temperature on the first piece are virtually eliminated by use of the VP systems. 25
  26. 26. Profiling Pb RSS (Ramp-Soak-Spike) for lead and RS (Ramp-to-Spike) for lead free are the top reference profiles for many applications .  These profiles were characterized for each board using thermocouples at multiple locations on and around the device. 26
  27. 27. Profiling Unique profiles were developed for each group of characterized products, based on:  Thermal mass  Distribution of copper planes  Loading patterns (distance between boards as they are loaded in the oven)  IPC/JEDEC J-STD-020 classification. 27
  28. 28. Profiling BGAs /CSPs holes are drilled in the inner and outer rows of BGA pads  BGA ball temperatures of inner and outer rows must be within 2ºC of each other. Minimum of 2 thermocouples per BGA/CSP attached to a RF high temperature resistant recording device PTP profiler which travels through the vapor phase reflow oven with the panel under test. Large components with high thermal mass require higher peak temperature for longer durations and smalltemperature sensitive components require lower peak temperatures for shorter durations. Four to six thermocouples should be attached at various component lead locations to represent the lowest tohighest thermal-mass 28
  29. 29. Vapor Phase Samples Cross-Section Samples 29
  30. 30. Vapor Phase Samples PCBA, Double sided, 12 Layers, with BGA‘s 30
  31. 31. Vapor Phase Samples SEM Solder Joints Samples 31
  32. 32. Conclusions Restricted resources, rising energy cost, increased awareness on the environment, increased demand for qualityat low operating cost, and the migration to PB-free components, urge a change towards vapor phase as the processof choice. Engineers are being challenged to establishes good processes up front, with minimal interference to operations. VP soldering process assists the Engineer to get it right the first time, minimizing production interruptions. VP reflow in inert gas atmosphere is not only a benchmark for other procedures but it defines an own uniquestandard. Vapor Phase reflow soldering is a technology from yesterday that will certainly see its comeback in the Lead Free,Lean manufacturing environment of today. 32