infrared reflow

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(1) First generation-hot plate reflow oven
(2) Second generation-infrared reflow oven
80% of the energy in thermal energy is emitted in the form of electromagnetic waves – infrared rays. Its wavelength is between 0.7~0.8um and 1mm, the upper limit of visible light. 0.72~1.5um is near infrared; 1.5~5.6um is mid-infrared; 5.6~1000um is far infrared, and microwave is above the far infrared.
The mechanism of heating: When the vibration frequency of the infrared wavelength is consistent with the vibration frequency of the molecules of the radiated object, resonance will occur. The intense vibration of the molecules means that the object is heating up. The wavelength is 1~8um.
The fourth zone has the highest temperature setting, which can cause the temperature of the welding zone to rise rapidly and increase the wetting force. Advantages: Rapid hydration of flux, organic acids and halides improves wetting ability; the radiation wavelength of infrared heating is similar to the absorption wavelength, so the substrate heats up quickly and the temperature difference is small; the temperature curve is easy to control and has good elasticity; infrared heater High efficiency and low cost.
Disadvantages: poor penetration, shadow effect – uneven heat.
Countermeasure: Add hot air circulation during reflow soldering.
(3) Third generation-infrared hot air reflow soldering.
The speed of convection heat transfer depends on the wind speed, but excessive wind speed will cause component displacement and promote oxidation of solder joints. The wind speed should be controlled at 1.0~1.8m/s. There are two forms of hot air generation: axial fan generation (easy to form laminar flow, and its movement causes unclear boundaries between temperature zones) and tangential fan generation (the fan is installed outside the heater, generating panel vortices so that each temperature zone can be accurately control).
Basic structure and temperature curve adjustment:

  1. Heater: tube heater, plate heater aluminum plate or stainless steel plate;
  2. Transmission system: heat-resistant PTFE fiberglass cloth;
  3. It runs smoothly and has good thermal conductivity, but cannot be connected. It is suitable for small hot plate stainless steel mesh. It is suitable for double-sided PCB and cannot be connected. Chain guide rail can realize connected production.
  4. Forced convection system: temperature control system.
    Process flow
  5. Single panel:
    (1) Print solder paste on the mounting and plug-in pads at the same time;
    (2) Place SMC/SMD;
    (3) Insert TMC/TMD;
    (4) Reflow soldering.
  6. Double panel
    (1) Solder paste-reflow process to complete the welding of double-sided chip components;
    (2) Then apply solder paste on the through-hole component pad on side B;
    (3) Invert the PCB and insert through-hole components;
    (4) The third reflow soldering.
    Precautions
  7. Compatibility with SMB, including the wettability of the pad and the heat resistance of SMB;
  8. The quality of the solder joints and the tensile strength of the solder joints;
  9. Welding working curve:
    Preheating zone: The heating rate is 1.3~1.5 degrees/s, and the temperature rises to 150 degrees within 90~100s.
    Insulation zone: temperature is 150-180 degrees, time is 40-60 seconds.
    Reflow zone: It takes 10 to 15 seconds to go from 180 to the maximum temperature of 250 degrees, and it takes about 30 seconds to return to the heat preservation zone for rapid cooling.
    Lead-free soldering temperature (tin, silver, copper) is 217 degrees.
  10. Flip Chip reflow soldering technology F.C.
    Vapor phase reflow soldering
    Also known as Vapor Phase Soldering (VPS), it was originally used for the welding of thick film integrated circuits in the United States. It has the advantages of fast heating speed and uniform and constant temperature. However, the heat transfer medium FC-70 is expensive and requires FC-113 , and it is an ozone layer depleting substance. advantage:
  11. Vapor phase latent heat release is insensitive to the physical structure and geometry of SMA, allowing components to be evenly heated to the welding temperature;
  12. The welding temperature remains constant, without the need for temperature control, to meet the needs of welding at different temperatures;
  13. The vapor phase field of VPS is saturated steam with low oxygen content;
  14. High thermal conversion rate.
    Laser reflow
  15. Principle and characteristics: Use laser beam to directly irradiate the welding part.
  16. The solder joint absorbs light energy and converts it into heat energy, heating the welding part and melting the solder.
  17. Type: solid YAG (aluminum garnet) laser.
    Common knowledge
  18. Generally speaking, the temperature specified in the SMT workshop is 23±7℃;
  19. When solder paste printing, the required materials and tools are: solder paste, steel plate, scraper, wiper paper, dust-free paper, cleaning agent, mixing knife;
  20. The commonly used solder paste composition is Sn96.5%/Ag3%/Cu0.5%;
  21. The main ingredients in solder paste are divided into two parts: tin powder and flux;
  22. The main function of flux in welding is to remove oxides, destroy the surface tension of molten tin, and prevent re-oxidation;
  23. The volume ratio of tin powder particles and flux (flux) in the solder paste is about 1:1, and the weight ratio is about 9:1;
  24. The principle of taking solder paste is first in, first out;
  25. When the solder paste is opened and used, it must go through two important processes of warming and stirring;
  26. Common production methods of steel plates are: etching, laser, and electroforming;
  27. The full name of SMT is Surface mount (or mounting) technology, which in Chinese means surface adhesion (or mounting) technology;
  28. The full name of ESD is Electro-static discharge, which means electrostatic discharge in Chinese;
  29. When making an SMT equipment program, the program includes five parts: PCB data; Mark data; Feeder data; Nozzle data; Part data;
  30. The melting point of lead-free solder Sn/Ag/Cu 96.5/3.0/0.5 is 217C;
  31. The controlled relative temperature and humidity of the parts drying box is <10%;
  32. Commonly used passive components (PassiveDevices) include: resistors, capacitors, inductors (or diodes), etc.; active components (ActiveDevices) include: transistors, ICs, etc.;
  33. Commonly used SMT steel plates are made of stainless steel;
  34. The thickness of commonly used SMT steel plates is 0.15mm (or 0.12mm);
  35. The types of electrostatic charges include friction, separation, induction, electrostatic conduction, etc.; the impact of electrostatic charges on the electronics industry is: ESD failure, electrostatic pollution; the three principles of static elimination are electrostatic neutralization, grounding, and shielding;
  36. Inch size length x width 0603=0.06inch0.03inch, metric size length x width 3216=3.2mm1.6mm;
  37. The 8th code “4” of ERB-05604-J81 indicates 4 circuits, and the resistance is 56 ohms. The capacitance value of capacitor ECA-0105Y-M31 is C=106PF=1NF =1X10-6F;
  38. The full name of ECN in Chinese is: Engineering Change Notice; the full name of SWR in Chinese is: Special Needs Work Order, which must be countersigned by all relevant departments and distributed by the document center to be valid;
    The specific content of 22.5S is sorting, rectifying, sweeping, cleanliness, and quality;
  39. The purpose of PCB vacuum packaging is to prevent dust and moisture;
  40. The quality policy is: comprehensive quality control, implementation of the system, and providing the quality required by customers; full participation and timely processing to achieve the goal of zero defects;
  41. The three-no policy on quality is: do not accept defective products, do not manufacture defective products, and do not distribute defective products;
  42. The seven QC techniques include checklist, hierarchy method, Plato, cause and effect diagram, scatter diagram, histogram, and control chart;
  43. The ingredients of solder paste include: metal powder, solvent, flux, anti-sag agent, and activator; by weight, metal powder accounts for 85-92%, and by volume, metal powder accounts for 50%;
  44. The solder paste must be taken out of the refrigerator and allowed to warm up before use. The purpose is to return the temperature of the refrigerated solder paste to normal temperature to facilitate printing. If the temperature is not restored, the defect that is likely to occur after PCBA enters Reflow is tin beads;
  45. The file supply modes of the machine include: preparation mode, priority exchange mode, exchange mode and quick connection mode;
  46. SMT PCB positioning methods include: vacuum positioning, mechanical hole positioning, double-side clamp positioning and board edge positioning;
  47. The silk screen (symbol) of a resistor is 272 and the resistance is 2700Ω. The symbol (silk screen) of a resistor with a resistance of 4.8MΩ is 485;
  48. The silk screen on the BGA body contains information such as manufacturer, manufacturer material number, specifications, Datecode/(Lot No);
  49. The pitch of 208pinQFP is 0.5mm;
  50. Among the seven QC techniques, the fishbone diagram emphasizes finding causal relationships;
  51. CPK refers to: process capability under actual conditions;
  52. The flux begins to evaporate in the constant temperature zone for chemical cleaning;
  53. The ideal mirror relationship between the cooling zone curve and the reflow zone curve;
  54. Sn62Pb36Ag2 solder paste is mainly used for ceramic boards;
  55. Rosin-based fluxes can be divided into four types: R, RA, RSA, and RMA;
  56. The RSS curve is heating → constant temperature → reflux → cooling curve;
  57. The PCB material we currently use is FR-4;
  58. The PCB warpage specification does not exceed 0.7% of its diagonal;
  59. STENCIL production laser cutting is a method that can be reworked;
  60. The diameter of the BGA ball commonly used on computer motherboards is 0.76mm;
  61. The ABS system is absolute coordinates;
  62. The error of ceramic chip capacitor ECA-0105Y-K31 is ±10%;
  63. The computer PCB used is made of: fiberglass board;
  64. The diameter of SMT parts packaging tape and reel is 13 inches and 7 inches;
  65. SMT generally has steel plate openings that are 4um smaller than PCB PAD to prevent solder ball defects;
  66. According to the “PCBA Inspection Specifications”, when the dihedral angle is >90 degrees, it means that the solder paste has no adhesion to the wave solder body;
  67. If the humidity on the humidity display card after the IC is unpacked is greater than 30%, it means that the IC is damp and absorbs moisture;
  68. The correct weight and volume ratios of tin powder and flux in the solder paste ingredients are 90%:10%, 50%:50%;
  69. Early surface mount technology originated from the military and avionics fields in the mid-1960s;
  70. Currently, the contents of Sn and Pb in the most commonly used solder pastes for SMT are: 63Sn 37Pb; the eutectic point is 183°C.
  71. The feeding distance of a common paper tape tray with a width of 8mm is 4mm;
  72. In the early 1970s, a new type of SMD appeared in the industry, which was a “sealed pinless chip carrier” and was often abbreviated as LCC;
  73. The resistance of the component with symbol 272 should be 2.7K ohms;
  74. The capacitance value of 100NF component is the same as 0.10uf;
  75. The most widely used electronic component material of SMT is ceramic;
  76. The maximum temperature of the reflow furnace temperature curve is 215C, which is the most suitable;
  77. When inspecting the tin furnace, the temperature of the tin furnace is 245°C.
  78. The opening patterns of steel plates are square, triangular, circular, star-shaped, and straight-shaped;
  79. Whether the SMT segment exclusion has directionality or not;
  80. The solder paste sold on the market actually only has a viscosity time of 4 hours;
  81. The rated air pressure generally used by SMT equipment is 5KG/cm2;
  82. Tools for SMT parts repair include: soldering iron, hot air extractor, desoldering gun, and tweezers;
  83. QC is divided into: IQC, IPQC, FQC, OQC;
  84. High-speed placement machines can mount resistors, capacitors, ICs, and transistors; the packaging methods are Reel and Tray. Tube is not suitable for high-speed placement machines;
  85. Characteristics of static electricity: small current, greatly affected by humidity;
  86. What kind of welding method should be used when the front PTH and back SMT pass through the tin furnace? Disturbed double wave soldering;
  87. Common inspection methods for SMT: visual inspection, X-ray inspection, machine vision inspection, AOI optical instrument inspection;
  88. The heat conduction mode of ferrochrome repair parts is conduction and convection;
  89. The main components of BGA material’s solder balls are Sn90 Pb10, SAC305, and SAC405;
  90. Steel plate manufacturing methods: laser cutting, electroforming, chemical etching;
  91. According to the temperature of the soldering furnace: use a thermometer to measure the applicable temperature;
  92. When the SMT semi-finished products from the soldering furnace are exported, their welding status is that the parts are fixed on the PCB;
  93. The development history of modern quality management TQC-TQA-TQM;
    79.ICT testing is a bed of needles test;
  94. ICT testing can test electronic components using static testing;
  95. The characteristics of solder are that the melting point is lower than other metals, the physical properties meet the welding conditions, and the fluidity at low temperatures is better than other metals;
  96. If the soldering furnace parts are replaced and the process conditions change, the measurement curve must be re-measured;
  97. Siemens 80F/S is a relatively electronically controlled transmission;
  98. The solder paste thickness gauge uses Laser light to measure: solder paste degree, solder paste thickness, and solder paste printed width;
  99. SMT parts feeding methods include vibrating feeder, disc feeder, and tape and reel feeder;
  100. What mechanisms are used in SMT equipment: cam mechanism, side rod mechanism, screw mechanism, sliding mechanism;
  101. If the visual inspection section cannot be confirmed, which operation BOM, manufacturer confirmation, and sample plate need to be followed;
  102. If the parts packaging method is 12w8P, the counter Pinth size must be adjusted by 8mm each time;
  103. Types of separate welding machines: hot air separate welding furnace, nitrogen separate welding furnace, laser separate welding furnace, infrared separate welding furnace;
  104. Methods that can be used for trial production of SMT parts samples: streamlined production, fingerprint machine placement, and fingerprint hand placement;
  105. Commonly used MARK shapes include: circle, “ten” shape, square, rhombus, triangle, and swastika;
  106. Due to improper setting of Reflow Profile in the SMT section, the parts may be slightly cracked in the preheating area and cooling area;
  107. Uneven heating at both ends of SMT parts can easily cause: empty welding, misalignment, and tombstones;
  108. The cycle time of high-speed machines and general-purpose machines should be as balanced as possible;
  109. The true meaning of quality is to do it right the first time;
  110. The placement machine should place small parts first and then large parts;
  111. BIOS is a basic input and output system, the full English name is: Base Input/Output System;
  112. SMT parts are divided into two types: LEAD and LEADLESS based on whether the parts have legs;
  113. There are three basic types of common automatic placement machines, continuous placement type, continuous placement type and mass transfer placement machine;
  114. It can be produced without LOADER in the SMT process;
  115. The SMT process is a board feeding system-solder paste printing machine-high-speed machine-general-purpose machine-separate flow soldering-board collecting machine;
  116. When temperature and humidity sensitive parts are opened, the color displayed in the circle on the humidity card is blue, and the parts can be used;
  117. The dimension specification of 20mm is not the width of the tape;
  118. Reasons for short circuit due to poor printing during the manufacturing process: a. Insufficient metal content in the solder paste, causing collapse; b. Too large openings in the steel plate, causing tin
  119. The amount is too much c. The quality of the steel plate is poor and the soldering is poor. Replace the laser cutting template d. There is solder paste remaining on the back of the Stencil. Reduce the scraper pressure and use appropriate VACUUM and SOLVENT;
  120. The main engineering purposes of each area of the general reflow oven Profile: a. Preheating area; engineering purpose: volatilization of the solder paste neutralizing agent. b. Uniform temperature zone; engineering purpose: flux activation, removal of oxides; evaporation of excess water. c. Reflow area; engineering purpose: solder melting. d. Cooling area; engineering purpose: alloy solder joints are formed, and part feet and pads are integrated;
  121. The main causes of solder beads in the SMT process are: poor PCB PAD design, poor steel plate opening design, excessive component placement depth or component placement pressure, excessive rise slope of the Profile curve, solder paste collapse, and solder paste viscosity that is too low .

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