1. High Performance Printed
Circuit Boards
By Joseph Y. Lee
Samsung Electro-Mechanics

2. Chapter - 4
Advanced Ceramic
Substrates for
Microelectronic
Systems

3. Desired Substrate Properties
 High electrical resistivity
 High thermal conductivity
 Resistance to temperature
 Inert to chemical corrosion
 Cost

4. Selected Ceramics
Table 4.1 Melting Point of Selected Ceramics
Material Melting Point °C
SiC 2700
BN 2732
AlN 2232
BeO 2570
Al3O2 2000

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. Definitions
 Surface roughness; measure of the
surface microstructure
 Camber; measure of the deviation from
flatness (red line).
deviation

7. Substrates Rules:
 Thicker substrates – less
camber
 Squares are better than
rectangles
 Pressed methods are better.

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. 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. 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. 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. 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. Thin Films
Several layers of metal are formed by vacuum deposition techniques –
sputtering or evaporation, or by electro-plating. One example method is
DC sputtering as shown in figure.

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. 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. 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 Cu
Composite materials is combination of metal
and ceramics.

17. Multilayer Substrates Structures
 Thick films – limited to 3 layers
 Thin films – expensive
 Cu – single layers
Types of Multilayer substrates
- HTCC
- LTCC
- AlN

18. Chapter – 5
Flexible Printed
Circuits
They are printed circuits that are fabricated on a
thin flexible-based material and are usually
constructed with a non-reinforced polymeric
material.

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. Introduction

21. Categories of Flexible Circuits
*Traditional Flexible Circuits
*Thick Film Circuit
*HDI Flexible Circuits
*TAB (TBGA)
*Wireless Suspension
*Flexible Interposer
(*COF Substrates)

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. HDI Flexible Circuits
Traditional
200 Flexible Circuits
150
Via
Diameter 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. TAB (Tape Automated Bonding)
Typical single layer fine pitch TAB (Wus)

25. Wireless Suspension
Wireless suspension with a high density flex circuit
(KR Precision)

26. Flexible Interposer
IC Substrates
(Ibiden)

27. PWB Production by Revenue in Japan
(METI, DKN Research)
600000
Rigid s/s
Rigid d/s
500000 Rigid Multi
Flex
400000
300000
200000
100000
0
Year

28. Global Market Share of Flexible Circuits
(2003, Total 7 billion US$, DKN Research)
Japan
U.S.A.
Korea
Europe
Taiwan
Singapore

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. Clamshell
Swing &
Slide
※ SEMBrid 를 이용하여 고기능 / 스타일 폰에 적용
가능

31.  Rigid-Flex PCB (SEMBrid)
Top Bottom
LCP
PPG
Cu
Cover Lay
PSR
Flexible PCB

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. 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. Finished Flexible Circuits
 Low dielectric constant
 Low dissipation loss
 High volume resistivity
 High surface resistivity

35. Materials

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. 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. 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. 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. 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. 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. 5 Distinct Layers
 Base dielectric film
 Conductor layer
 Cover-coat film
 Two layers of adhesives
 Accounts of 50% of total flexural
thickness

43. Adhesives

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. 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. 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. 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. 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. 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. 감사합니다