Properties of Some Typical Substrate Materials

MIC Manufacturing Technology Thin-Film Module

Thick-Film Module

Medium-Film Module

Monolithic Technology

Circuit is accomplished by a plate-through technique or an etch-back technique.

1) Thick-film patterns are printed and fired on the ceramic substrate.

2) Printed circuit technique is used to etch the desired pattern in a plastic substrate.

Above technologies are suitable for HMIC productions.

This technology is suitable for MMIC productions.

Properties of Various Manufacturing Technology

Multi-Chip Modules (MCM) MCM provides small, high precision interconnects among

multiple ICs to form a cost-effectively single module or package.

Four dominant types of MCM technologies:

1) MCM-L having a laminated PCB-like structure.

2) MCM-C based on co-fired ceramic structures similar to thick-film modules.

3) MCM-D using deposited metals and dielectrics in a process very similar to that used in semiconductor processing.

4) MCM-C/D having deposited layers on the MCM-C base

Advantages of an MCM over a PCB are :

1) Higher interconnect density.

2) Finer geometries enables direct chip connect.

3) Finer interconnect geometries enables chips placed closer together and it results in shorter interconnect lengths.

Comparison of MCM Technologies

Low Frequency Characters of Microstrip Line

Microstrip line is the most popular type of planar transmission lines, primarily because it can be fabricated by photolithographic processes and is easily integrated with other passive and active RF devices.

When line length is an appreciable fraction of a wavelength (say 1/20th or more), the electric requirements is often to realize a structure that provides maximum signal, or power, transfer.

Example of a transistor amplifier input network

Microstrip components

Transmission line

Discontinuities

•Step

•Mitered bend

•Bondwire

•Via ground

Microstrip Line

The most important dimensional parameters are the microstrip width w, height h (equal to the thickness of substrate), and the relative permittivity of substrate r.

Useful feature of microstrip :

DC as well as AC signals may be transmitted.

Active devices and diodes may readily be incorporated.

In-circuit characterization of devices is straightforward to implement.

Line wavelength is reduced considerably (typically 1/3) from its free space value, because of the substrate fields. Hence, distributed component dimensions are relatively small.

The structure is quite rugged and can withstand moderately high voltages and power levels.

Although microstrip has not a uniform dielectric filling, energe transmission is quite closely resembles TEM; it’s usually referred to as ‘quasi-TEM’.

12

1101

1

1

CcLcL

cCC

LZ

Characteristic Impedance ZZ00

For low-loss microstrip lines,

For air-filled microstrip lines,

C

LZ 0

We can derive

1

01

10 ;

1

C

cZ

CCcZ eff

eff

The statically derived results are quite accurate where frequency is below a few GHz.

The static results can still be used in conjunction with frequency-dependent functions in closed formula when frequency at higher frequency.

Electromagnetic Analysis Using Quasi-Static Approach (Quasi-TEM Mode)

Procedure for calculating the distributed capacitance:

)1,(

),( LawsGauss'

),( and 0at ,,for BCs

0),( :equation sLapace'

1

0

000

00

0000

02

r

rc

ctc

tt

ttt

tttt

tt

h

wfC

h

wf

V

QCsdDQ

ED

VE

yxV hy yDEV

yxV

Effective Dielectric Constant ),()(

1

2r

peff h

wg

C

C

v

c

For very wide lines, w / h >> 1r

w

h

r

w

h

reff

For very narrow lines, w / h << 1

2

1 r

eff

1q

2/1q

where filling factor qq represents the ratio of the EM fields inside the substrate region, and its value is between ½ and 1. Another approximate formula for q is

1

1 )1( 1

r

effreff qq

We can express eff as

Planar Waveguide Model

120 where

)(

000

00

effeffw

hZ

)1(

)1(

reff

effrq

(provided by K.C. Gupta, et. al.)

r

eff

(Parallel-Plate Model)

1r

reff 1

Conductor Loss c

In most microstrip designs with high r, conductor losses in the strip and ground plane dominate over dielectric and radiation losses.It’s a factors related to the metallic material composing the ground plane and walls, among which are conductivity, skin effect, and surface roughness.Relationships:

. minimize todepth skin the times5~3 angreater th be should thicknessstrip The

) line, idealized In (ty conductivi toopposite

surface. substrate theof roughness ,

c

c

c w

h

Dielectric Loss d

To minimize dielectric losses, high-quality low-loss dielectric substrate like alumina, quartz, and sapphire are typically used in HMICs.In MMICs, Si or GaAs substrates result in much larger dielectric losses (approximately 0.04 dB/mm).

Radiation Loss r

Radiation loss is major problem for open microstrip lines with low . Lower (5) is used when cost reduction is a priority, but it lead to radiation loss increased.The use of top cover and side walls can reduce radiation losses. Higher substrate can also reduce the radiation losses, and has a benefit in that the package size decreases by approximately the square root of . This benefit is an advantage at low frequency, but may be a problem at higher frequencies due to tolerances.

r) wavenumbespace-(free / where

)(Np/m tan2

1 tan

2

1 tan

2

1

tan2

1)

tan(

2

1)(

2

1

2

000

eff0c00

0

ck

k

LCLCC

LC

GZ

ceffc

cc

d

However, the dielectric loss should occur in the substrate region only, not the whole region. Therefore, d should be modified as

)(m )1(2

tan)1(

tan2

1

)1(

)1(tan

2

1

1-0

00

reff

ceffr

ceffreff

effrceffd

k

kkq

)(Np/m 2

12

2 000 wZ

R

Zw

R

Z

R ssc

Formulations of Attenuation Constant

How to evaluate attenuation constant Method 1 : in Chapter 2.14 ; is calculated from RLCG values of material.

Method 2: Perturbation method

Method 3: is calculated from material parameters.

rdc

dl

dZ

Z

Rsc

0

02

where c is attenuation due to conductor loss d is attenuation due to dielectric lossr is attenuation due to radiation loss

02

)0(

P

zPl where Pl is power loss per unit length of

line, P0is the power on line at z=0 plane.

TM waves)or TE(for Np/m :unit ;2

tan2

k

d

TEM waves)(for Np/m :unit ;2

tan

k

d

Combined Loss Effect : linearly combined quality factors (Q)

rdc QQQQ

1111

Recommendations

1) Use a specific dimension ratio to achieve the desired characteristic impedance. Following that, the strip width should be minimized to decrease the overall dimension, as well as to suppress higher-order modes. However, a smaller strip width leads to higher losses.

2) Power-handling capability in microstrip line is relatively low. To increase peak power, the thickness of the substrate should be maximized, and the edges of strip should be rounded ( EM fields concentrate at the sharp edges of the strip).

3) The positive effects of decreasing substrate thickness are :a) Compact circuitb) Ease of integrationc) Less tendency to launch higher-order modes or radiationd) The via holes drilled through dielectric substrate

contributing smaller parasitic inductances However, thin substrate while maintaining a constant Z0

must narrow the conductor width w, and it consequently lead to higher conductor losses, lower Q-factor and the problem of fabrication tolerances.

4) Using higher substrate can decrease microstrip circuit dimensions, but increase losses due to higher loss tangent. Besides, narrowing conductor line have higher ohmic losses. Therefore, it is a conflict between the requirements of small dimensions and low loss. For many applications, lower dielectric constant is preferred since losses are reduced, conductor geometries are larger ( more producible), and the cutoff frequency of the circuit increases.

5) For microwave device applications, microstrip generally offers the smallest sizes and the easiest fabrication, but not offer the highest electrical performance.

Design a microstrip line by the method of

“Approximate Graphically-Based Synthesis”

Example1: Design a 50 microstrip line on a FR4 substrate( r

=4.5).

Assume eff = r =4.5

From Zo1 curve w/h=1.5

From q-curve q=0.66

eff = 1+q (r +1)=1+0.66(4.5-1)=3.31

2nd iteration

eff = 3.31

From Zo1 curve w/h=1.7

From q-curve q=0.68

eff = 1+q (r +1)=1+0.68(4.5-1)=3.38

3rd iteration

Stable result w/h=1.88; eff =3.39

Solution

9131.350001 effZZ

01 0 50 4.5 106effZ Z

1 ,

)/444.1( ln667.0393.1)(

120

1 ),4

8ln(

60

eff

0

h

w

hwhw

h

w

h

w

w

h

Z eff

Synthesis procedure: Give Z0 to find w / h.

rrr

rr

rr

r

ZB

ZA

h

wBBB

h

w

h

w

0

0

2A

A

2

377 ),

11.023.0(

1

1

2

1

60 where

2 ,61.0

39.0)1( ln2

1)12( ln1

2

2 2e

8e

Analysis procedure: Give w / h to find eff and Z0.

)/( 1212

1

2

1

whrr

eff

(provided by I.J. Bahl, et. al.)

Formulas for Quasi-TEM Design Calculations

Example2: Calculate the width and length of a microstrip line for a 50 Characteristic impedance and a 90° phase shift at 2.5 GHz. The substrate thickness is h=0.127 cm, with eff =2.20.

Guess w/h>2

Solution

081.361.0

39.0)1( ln2

1)12( ln1

2

985.72

377

0

rr

r

r

BBBh

w

ZB

Matched with guess

Then w=3.081h=0.391 (cm)

87.1)/( 1212

1

2

1

wh

rreff

The line length, l, for a 90° phase shift is found as

(cm) 19.2)180/(90

)(m 35.522 90

0

1-00

kl

cfklkl

eff

eff

Microstrip on an Dielectrically Anisotropic Substrate

capacitnce plate-parallel denotes )/(

capacitnce fringing denotes )/(

where;

4.900

06.110

004.9

00

00

00

00

00

00

0y

0

||

hwC

hwCC

CC

CC

y

iif

yf

yyfireq

Sapphire

z

y

x

10010 and 10/1.0

range thethroughoutaccuracy %5.0

;)]/10[log(39.01

21.112

0

2

Zhw

hweff

Empirical formula

Curve : i =10.6 ;

Curve : used req

formula