3. Definitions
Laminates – combination of a resin system and a
reinforcement material.
Glass transition temperature (Tg) – temperature
such that resin behaving more like a gel or high
viscosity liquid rather than a solid.
Loss tangent or dissipation factors – power loss
through the laminate material
Epoxy - a thermosetting resin; used chiefly in
strong adhesives and coatings and laminates
4. Cross section of FR-4 and CCL
epoxy
C
u
resin
CC FR-4 glass
L fibers
void
epoxy
5. Bismaleimide Tiazine (BT) Epoxy-Based
Laminates
Low cost
Used in FR-4.
Less water absorption compared to polyimide
However, low Tg. Less tolerate of high
temperatures.
Tradeoffs- Difficulty in drilling causes
microcracks
Tradeoffs - brittle when lower % of resin
6. Table 1.1 High Tg Laminate Systems
Resin Reinforcement Tg (°C)
Bisamaleimide triazine-epoxy Woven E-glass 170-220
Polymide Woven E-glass 200 min
Polymide Nonwoven aramid 220 min
Polymide Woven quartz 250 min
Cyanate ester Cross-plied aramid 230 min
Cyanate ester Woven S-2 glass 230 min
7. Polyimide
Excellent toughness – superior adhesion to
copper
Good processability
Highest Tg – reduce overall manufacturing
costs
Tradeoff- very expensive
Another tradeoff – absorbs water
10. PTFE (Teflon)
Low dielectric constant and low loss tangent
Nonpolar and hydrophobic
E-glass widely use
Costs cheaper than polyimide
Tradeoffs – CTE problems caused plated-through
holes failures
z-axis expansion and
contraction
11. Choice of Materials Considerations
Cost
Loss tangent must be low.
CTE (Coefficient Temperature of Expansion)
Tg (Glass Transition Temperature)
Modulus of tensile strength
Water absorption
Dielectric constant – depends applications
12. Chapter – 2
Microvias, Built-Up
Multilayers, and High
Density Circuit Boards
13. Definitions
Plated-through holes – connect together circuits on
both sides of the board by means of a drill
Multilayering – separate two-layer circuits could be
laminated together and then connected to each other
with plated-through holes
Buried via – made by drilling and plating a two-sided
board and then laminating into a multilayer
Blind via – connects outer layer circuit to an interior
layer without disturbing the layers below the interior
layer
Microvia – very small hole or via, generally by a non-
mechanical means to connect two layers of circuitry.
15. Three Laser Systems
CO2
Fastest system
Form vias in organic and glass reinforced dielectrics
Cannot penetrate Cu
UV-YAG
Slower
Can penetrate Cu
Excimer
Highest via resolution
Slowest
Overall – less stringent cleanliness requirements and no
photomask is required. Cost is lower than photoprocess.
16. Sequential vs. Parallel Processes
Sequential – circuit layers built up one at a time
(laser process)
Parallel – individual layers are separately made,
then laminated all at once (B2IT process)
Sequential yield = 0.95 * (0.92)4 = 68% yield
Parallel yield = 0.95 * (0.92)2 = 80% yield
17. Microvia
Much smaller
Possible to pack much more
functionality in smaller space
More efficient circuit routing
Less distortion to rise time
Lower resistance by 17x
Less signal delay at 100MHz and above
18. Three Processes for Microvia
Via non-uniform,
Both photovia and slow process
laservia have good
anistropic etching
20. Considerations
Again, cost.
Laser vs. Photo – depending on number
of microvias
Yield between photovia vs. B2IT
Microvias is the way to go.
Reduction of # of layers is required to
reduce costs for microvias.
22. What Are RF and
Microwaves?
They are analog signals or AC signals.
Digital signals are 0’s and 1’s.
0 – 0 volt, 1 – 2 volts.
Wavelengths between 0.1 to 30cm.
Cell phones are hand held radios. They
receive and transmit radio signals.
Radio waves are electro-magnetic waves.
An radio antennae is an inductor.
28. IC Chip – Parasitic
Transmission Lines
Passives on Printed Circuit Board used to
correct reflectivity of parasitic transmission
lines in IC chip.
Why can we put
Ex. IC Chip with 4.5 km of metal lines in Pentium. the passives in
Metal lines form parasitic transmission lines the IC Chip?
29. Via Structures
Blind pad Blind Buried Staggered Staircase Spiral
Metal lines and vias embedded inside the PCB board do form parasitic
transmission lines as well. Passives are used to correct this.
31. Microstrip
Advantage - Most widely used. Excellent integration
with chip and lumped elements. Multilayers are
possible. Ground plane isolate the microstrip.
Disadvantage - Line losses are somewhat higher with
poorer isolation between circuits. It is unshielded and
some radiation occurs for thicker substrates depending
on dielectric constant and frequency.
32. Stripline
Advantage - No fields extend outside ground plane. Works
well with multilayers and well-shielded.
Disadvantage – It is susceptible to unwanted modes.
Crosstalking may be a problem as well.
33. Coplanar Waveguide
Very good integration with chip and lumped elements.
Series and shunt connections are relatively easy.
Disadvantage – thick substrates are required to keep
structure away from the chasis. Integration with
multilayers is poor.
34. Conductor-backed Coplanar Waveguide
Advantage – It offers less radiation loss than a pure
microstrip line. Connections can be made at the I/O’s
with ground, signal, or ground probes.
Disadvantages - It does require metal vias or plated-
through holes to connect the coplanar grounds to the
backside ground. Structure is susceptible to
unwanted parasitic modes.
35. Slotlines and Coplanar Strips
Slotline Coplanar Strips
Easy integration with chip and lump element.
Combination with microstrip located on ground plane
guarantee constant 180° phase shifts independent of
frequency for certain circuits.
However, they do not integrate well with multilayers.
36. Definitions – LTCC and HTCC
LTCC (Low Temperature Co-fired Ceramic) –
a multilayer ceramic technology, which
processes the ability to embed the passive
elements, such as resistors, capacitors and
inductors into a ceramic interconnect package
while the active elements are mounted on the
top layer.
HTCC (High Temperature Co-fired Ceramic)
– differs from LTCC by high temperature of
1600°C while LTCC uses a temperature of
850 to 950°C.
37. LTCC vs. HTCC
HTCC er=10 while LTCC er=4 to 8.
tanδ HTCC < tanδ LTCC
Resistivity of refractory metals like W and Mo
for HTCC > resistivity of Ag metals for LTCC
HTCC is made up of alumina particles while
LTCC is made up of glass with some alumina.
Firing oven heating, HTCC temperature >
LTCC temperature
Time to heat HTCC > Time to heat LTCC
38. General Design Recommendations
Minimize # of conductor layers
Use the widest possible lines and
spaces.
Avoid using tracks that are not 0 or 90°
angles.
Amount of metal should be evenly
distributed.
39. Organic PWB’s
FR-4 is the most easily manufactured
laminate material.
Thick metal ground plane provide high
heat flow.
Lower costs compared to ceramics.
Dielectric constant and dissipation
factors, same as ceramics if not better.