High Performance Printed Circuit Boards - Lecture #2


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High Performance Printed Circuit Boards - Lecture #2

  1. 1. High Performance Printed Circuit Boards By Joseph Y. Lee Samsung Electro-Mechanics
  2. 2. Chapter - 4Advanced Ceramic Substrates for Microelectronic Systems
  3. 3. Desired Substrate Properties High electrical resistivity High thermal conductivity Resistance to temperature Inert to chemical corrosion Cost
  4. 4. Selected CeramicsTable 4.1 Melting Point of Selected CeramicsMaterial Melting Point °CSiC 2700BN 2732AlN 2232BeO 2570Al3O2 2000
  5. 5. Substrate Fabrication Roll compaction; large parallel rollers to form sheet. Tape casting; moving belt that flows under a knife edge. Powder pressing; powder into hard die cavity with high pressure through sintering process. Isostatic powder pressing; flexible die surrounded with water or glycerin and pressed up to 10,000 lb/in2 Extrusion; forced through a die. Very economical and produces thinner part.
  6. 6. Definitions Surface roughness; measure of the surface microstructure Camber; measure of the deviation from flatness (red line). deviation
  7. 7. Substrates Rules: Thicker substrates – less camber Squares are better than rectangles Pressed methods are better.
  8. 8. Thermal Properties Thermal conductivity (W/m-°C): q = -k (dT/dx) Specific heat (W-s/g-°C): c = dQ/dT Temp. coeff. of expansion (ppm/°C): α= [L 2) – L 1)] /[L 1)(T –T)] (T (T (T 2 1
  9. 9. Mechanical Properties Modulus of elasticity: E = TCE * ∆T Modulus of rapture (MPa): σ = Mx/I This can be used to measure tensile strength of thinned Si wafers. Maximum stress at the tip of crack: SM = 2 So < (a / ρt)0.5 Ratio of max. stress to applied stress: Kt = SM/S0 = 2 (a / ρt)0.5 Plain strain fracture toughness: KIC = Z Sc (pi * a)0.5 Critical force to cause breakage: Sc = KIC / [Z (pi * a)0.5]
  10. 10. Electrical Properties Resistivity: ρ= (1/σ) (Ω.cm) Current Density: J = σ E (A/cm2) Breakdown Voltage: (Volt) Dielectrics constant: ε (ratio) r Dielectric loss: tan(δ)
  11. 11. Metallization of Ceramic Substrates Thick film – additive process by which conductive, resistive, and dielectric patterns in the form of a viscous paste are screen printed, dried, and fired onto a ceramic substrate at an elevated temperature to promote adhesion of the film Thin film – subtractive process such that entire substrate is coated with several layers of metallization and unwanted material is etched away in a succession of selective photoetching processes. Copper 1) Direct bond copper 2) Plated copper 3) Active metal braze
  12. 12. Example of Thick Film Screen printing leaves metallic conductor, metal oxide resistor or dielectric insulator. Active element powders range from 1 to 10 µm in size. Adhesion element (glass and metal oxides) are used to bond active element on substrate. Organic binder is used to hold active and adhesion elements. Solvent is used to dilute thick organic binder.
  13. 13. Thin FilmsSeveral layers of metal are formed by vacuum deposition techniques –sputtering or evaporation, or by electro-plating. One example method isDC sputtering as shown in figure.
  14. 14. Copper Metallization Direct bond copper: bonded to alumina ceramic by placing Cu film heating to a temperature of 1065°C. Plated copper: Cu may be vacuum deposited by thin-film methods, screen printed by thick-film processes, or deposited by aid of a catalyst. Patterns formed by dry or wet photolithographic process. Active metal braze: one or more metals in the IV- B column are used. Braze formed of paste, powder, or a film. Ex. 70% Ti/15% Cu/15% Ni.
  15. 15. Substrate Materials Al2O3 – most common ceramic BeO – high thermal conductivity AlN – TCE matched with Si, high thermal conductivity Diamond – low specific heat BN – easily machinable, low TCE SiC – resistant to acids and bases, high thermal conductivity, low TCE
  16. 16. Composite Materials AlSiC – conductive with low TCE, softer than SiC, thermal conductivity 12 times greater than SiC Dymalloy – diamond with Cu20%/Ag80% alloy, melts at 800°C lower than CuComposite materials is combination of metal and ceramics.
  17. 17. Multilayer Substrates Structures Thick films – limited to 3 layers Thin films – expensive Cu – single layersTypes of Multilayer substrates- HTCC- LTCC- AlN
  18. 18. Chapter – 5 Flexible Printed CircuitsThey are printed circuits that are fabricated on a thin flexible-based material and are usually constructed with a non-reinforced polymeric material.
  19. 19. Outline Introduction  Mixtures of Materials solvents,  Fluorocarbons polymers, and  PET curing agents  PEN  Types  Polyimide  Problems  Aramids  Adhesiveless  Copper foils  Classification Adhesives  Cover Coat 5 distinct layers
  20. 20. Introduction
  21. 21. Categories of Flexible Circuits *Traditional Flexible Circuits *Thick Film Circuit *HDI Flexible Circuits *TAB (TBGA) *Wireless Suspension *Flexible Interposer (*COF Substrates)
  22. 22. Traditional flexible circuits Traditional flexible circuits #Single side #Double side #Multi-layer rigid/flex with MIL #Multi-layer rigid/flex for consumer (#Multi-layer flex) #Flex with stiffeners
  23. 23. HDI Flexible Circuits Traditional 200 Flexible Circuits 150ViaDiameter HDI Flex Circuits(micron) 100 50 Ultra HDI Flex Circuits 0 50 100 150 200 Circuit Density (micron pitch) Definition of HDI Flex Circuits
  24. 24. TAB (Tape Automated Bonding) Typical single layer fine pitch TAB (Wus)
  25. 25. Wireless Suspension Wireless suspension with a high density flex circuit (KR Precision)
  26. 26. Flexible Interposer IC Substrates (Ibiden)
  27. 27. PWB Production by Revenue in Japan (METI, DKN Research)600000 Rigid s/s Rigid d/s500000 Rigid Multi Flex400000300000200000100000 0 Year
  28. 28. Global Market Share of Flexible Circuits(2003, Total 7 billion US$, DKN Research) Japan U.S.A. Korea Europe Taiwan Singapore
  29. 29. Flex Circuit Production in Kore a (Electronic Times, Sep. 2003)Youngpoon 2003 2002 SI Flex Interflex 0 50 100 150 200 Revenue (million US$)
  30. 30. Clamshell Swing &Slide※ SEMBrid 를 이용하여 고기능 / 스타일 폰에 적용가능
  31. 31.  Rigid-Flex PCB (SEMBrid) Top Bottom LCP PPG Cu Cover Lay PSR Flexible PCB
  32. 32.  Rigid-Flex PCB Process (SEMBrid Process) RTOR Exposure RTOR Exposure & DES Line & DES Line Pre-Treatment Sheet Cutting Outgoing Inspection Pre-Treatment Sheet Cutting Outgoing Inspection & Sheet Cutting & Brown Oxide & Packaging & Sheet Cutting & Brown Oxide & Packaging Cover Lay Cover Lay Flexible & Cover Lay Cover Lay Flexible & Pre-Attachment Pre-Attachment Final Inspection Pre-Attachment Pre-Attachment Final Inspection Router Lay-Up & 11st Press Router Lay-Up & Press Lay-Up & 11st Press Lay-Up & Press st st & Checker & Post Punch & Post Punch & Checker & Post Punch & Post Punch Ele’less Au Plasma Treatment Ele’less Au Plasma Treatment & Marking & Marking Bonding Sheet Bonding Sheet PSR Process Pre-Attachment PSR Process Pre-Attachment B/S Lay-Up C/L Press B/S Lay-Up C/L Press & 22nd Press & Press nd Pre-treatment & Cu Surface Lay-Up Pre-treatment & Lay-Up C/L Pre-attachment LCP & V-Press C/L Pre-attachment & V-Press Trimming, CNC Drill DES(T) Trimming, CNC Drill DES(T) & DES(W) & Inspection & DES(W) & Inspection MVH De-smear CO2 Drill De-smear CO2 Drill & Cu Plating PTH & Cu Plating
  33. 33. Requirements for Flexible Printed Circuits Films High tensile strength (tear resistance) High tensile modulus (tear resistance) High melting point High Tg Good thermal stability Low CTE (dimensional stability) Low residual stresses (tear resistance)
  34. 34. Finished Flexible Circuits Low dielectric constant Low dissipation loss High volume resistivity High surface resistivity
  35. 35. Materials
  36. 36. Fluorocarbons Unmatched chemical inertness High thermal resistance Outstanding dielectric properties Tough mechanical properties Plated through-hole process difficult Electroless Cu do not adhere well Dimensional stability not as good as polyimide film
  37. 37. PET (Polyethylene terephthalate) Low cost compared to polyimide films Higher insulation resistance Greater tear strength Lower dielectric constant Lower moisture absorption Better dimensional stability Lower lamination temperature Melts below soldering temperature Difficult to bond to other laminates
  38. 38. PEN (Polyethylene Naphthalate) Tg = 120°C. Can withstand soldering temperature of 260°C for exposure of 5 to 10 seconds. Reaction product of 2,6 naphthalate dicarboxylate with ethylene glycol
  39. 39. Polyimide Ability to withstand heat of manual and automatic soldering Excellent thermal resistance Good insulators and high voltage barriers Absorb moisture Weak link in the polyimide laminate
  40. 40. Aramids Low initiating and propagation tear strength Dielectric constant of 1.6 to 2 Dissipation factor of 0.0015 Good dimensional stability Absorbs water or else it blisters seriously
  41. 41. Copper foils Electrodeposited copper foils  Starts with Cu solution being plated at very high deposition rates. Rolled anneal copper  Starts with Cu ingot and that are hot rolled to an intermediate gauge  Good flexural endurance  Resistance to fracturing in dynamic applications Low temperature anneal foils  Better flexural properties compared to RAC.  Better handling  higher yield strength, resist denting and crazing  Resist foil damage
  42. 42. 5 Distinct Layers Base dielectric film Conductor layer Cover-coat film Two layers of adhesives  Accounts of 50% of total flexural thickness
  43. 43. Adhesives
  44. 44. Adhesives- Mixtures of solvents, polymers, and curing agents Must be tack-free Must be thin – 0.001 to 0.002 inch Must have low residual volatile content Must be resistant to attack by chemicals Thermosetting to some degree Cured in reasonable time Limited shelf-life must be monitored
  45. 45. Types of Adhesives Acrylic adhesives  High heat resistance and good electrical properties  Dimensional stability and small hole drilling decrease yield. Polyimide and epoxy adhesives  Better heat resistance and electrical properties as good as acrylics  Better dimensional stability, better process, lower overall thickness  Increased laminate stiffness Polyester and phenolics  Cost effective  Good electrical properties, flexibility, fair heat resistance Butryal phenolics  Better heat resistance than polyester  Electrical properties poorer though, not as flexible
  46. 46. Problems with Adhesives Adhesives become insulator rather than insulator film Lacking in resistance delamination Poor moisture absorption Poor resistance to heat aging, discoloration, embrittlement, outgasing Poor insulation at elevated temperature
  47. 47. Adhesiveless Films Polyimide resin and Cu metal devoid of any nonpolyimide adhesive Thinner – 4 mils of savings Better thermal conductivity Greater flexibility and thinner circuits Thermal stress resistance of higher layer count rigid flexes is better as well.
  48. 48. Classification of Adhesiveless Cast to foil  Involves casting a liquid solution of polyamic acid onto surface of metal foil Vapor deposition on film  Cu is vaporized in a vacuum chamber and the metal vapors are deposited on polyimide film  Limited to a Cu thickness of 2µm. Sputter to film (vacuum chamber with Cu cathode)  Base metal undercoating of Cr, Ni, oxide  Slower process Plated on film (electroless metal chemistries)  Do not induce any thermal stresses  Much easier to handle
  49. 49. Cover Coat Protects circuit against corrosion and contamination Affords protection against mechanical damage Puts Cu on a single-sided flex on the neutral bending axis Helps anchor the terminal pads to the base dielectric
  50. 50. 감사합니다