Hybrid Circuits Technology
A brief outline
Sold in North America by:
Servoflo Corporation
75 Allen Street Lexington, MA 02421
Tel: 781-862-9572
September 2014
www.servoflo.com / info@servoflo.com
All the data included and presented are strictly confidential and belong to Metallux SA – Switzerland.
What Thick Film is

It is a Technology based on the deposition of conductive,
dielectric and resistive pastes by Screen Printing on ceramic
substrates (alumina Al2O3, typically 96% grade) or metallic
substrates (stainless steal, aluminium), with the aim to make
electronic circuits.
It is an “adjunctive” Technique, the pastes are added onto a
substrate only where the elements have to be, typical
conductive tracks thickness: 8-15 m
 It differs from Thin Film, that is a deposition of thin layers of
metals and metal oxides by evaporation and/or sputtering on
99% Alumina Al2O3 substrates and consecutive removing of
the unused areas by exposition and development.
It is an “subtractive” Technique (like for PCBs); typical
conductive tracks thickness: 1-3 m
2
Main differences between Thin and Thick Film
Characteristics
Thin Film
Thick Film
Conductor lines definition (m)
30-40
≥ 150
Quality of the definition
Very good
Sufficient
Resistor precision
0,1 %
0,5%
Few (5-10)
50-100
(% on the R value)
Resistor TCR (ppm)
Cost (*)
8-10
(*) Relative cost to a Thick Film circuit
Thin Film Au tracks
1
Thick Film Au tracks
Other than with a greater thickness, the Thick Film tracks are rougher and more uneven
3
What Hybrid Circuits are

The capability to integrate electronic components (SMD, bare
chips etc.) on Thick or Thin Film substrates is the historical
definition of ”Hybrid Circuits” (called also “Hybrids”)
Hybrid Circuits
Thick Film
circuits
Thin
Film
Circuits
Mixed
Technolgies
circuits (*)
Microelectronics devices
Hybrid
Circuits
Chip on
Board/Flex
SMT on
PCB/Flex
OTHERS
(**)
(*) Example: Thick Film circuit + Thin Film circuit in a package
(**) Microelectronics component on other special substrates
Note: MTX, just to simplify things, includes in the Hybrid Circuits family all the
electronics on PCBs (flex circuits included) as well
4
Hybrid Circuits hystory

The first Hybrid Circuits were born in the 70s when the Thick Film
technology developed simultaneously with the appearance of the
first SMD components. The objective was to have an electronic
substrate able to integrate components. The technology was (and it is
nowadays) able to make small resistors practically with each desired
value and good tolerance and reliability

Hybrids were born to supply the Military and Avionic market with HiRel circuits, to satisfy very harsh requirements
At that time the PCBs were not so reliable with the temperature and
their costs were still expensive.

Afterwards the Hybrids were introduced also in the Telecom and the
Automotive market, the technology was at the top of maturity in the
90s.

Time by time the PCB became more reliable, special High Tg materials
were developed, and SMT on PCBs wore away a large segment of
Hybrids market
5
Why to use an Hybrid Circuit

Hybrid Circuits are still designed for the following reasons:

High temperature (> 85°C) demand or harsh environmental
conditions demand (temperature + humidity etc.), typical, for
example, with Military microelectronics devices.

Low and Medium Power (around 2-3 kW) devices. Ceramic is a very
good heat dissipator

When functional trimming is required: it is possible to trim the
screen printed resistor on a circuits with electronic components to
adjust a Voltage, a Current or a Frequency Output

It is possible to use resistors and conductors tracks to create a power
generator (low power and medium power from hundred mWatt to
2-3 KWatt) when heating elements are needed

To make Ceramic Pressure Sensors: they are “hybrid circuits” !
6
Thick Film Hybrid characteristcs (1)

As we have already seen, it is possible to generate by screen
printing any passive element of an electronic circuit:
Conductive tracks

Resistors
Cross over on
Dielectric
It is possible to produce double side circuits connected with
metalized through holes, or multilayer circuits, that are made
by several conductor layers separated by dielectric layers
Conductor
Dielectric
Via fill
7
Thick Film Hybrid characteristcs (2)

It is possible to work several circuits in the same time with a
single layer

It is possible to screen print resistors that are trimmed by a
Nd:Yag laser to get the project value (called nominal value),
from few milliohms to Gohm, with tolerances till 0,5%
After firing the
resistor value
is between 50% to -10%
on respect the
expected value
After the
laser
trimming the
resistor takes
the nominal
ohmic value
8

Thick Film Hybrid characteristcs (3)
It is possible to assemble and
solder SMD components

It is possible to solder pins
(SIL, DIL, SMT shape etc.)

It is possible to screen print Gold pads
to connect signal silicon dies to a
substrate by standard wire bonding, or
Silver Palladium pads to connect
medium power dies (i.e: a Mosfet) by
Aluminium large diameter wire bonding
9
Metallux Hybrid Circuits Screem printing capability

Alumina thickness from 0.1 mm to 2.5 mm, substrate size
up to 4”x6”

Double side circuits with metalized through holes

Multilayers Hybrid Circuits with integrated trimmed
resistors

Several different metalization: Ag, AgPt, AgPd, Au etc.

Fine line definition to 150 µm – 150 µm width-space

Trimmed Resistors from mohms to Gohms

High thickness (> 50 µm) screen printed Silver for power
devices
10
Metallux Hybrid Circuits Assembly capability

Active / Passive SMT, from 0201 size to BGA and
µBGA

Chip & Wire: Die attach, Wedge and Ball Bonding,
Encapsulation, on all kind of substrates

Flip-chip: soldering and epoxy anisotropic attaching

Hot bar attach soldering process

Finishing and Encapsulation with conformal
coatings, epoxy and silicone resins
11
Main differences between Ceramic Thick Film substrates and PCBs
Characteristics
Hybrid Circuits
PCB (std. FR4)
Substrate
Allumina, Al2O3 96%
FR4: Fibre-Glass + epoxy resin
Conductive tracks
 Silver,
Silver-Palladium, SilverPlatinum, Au
Conductive tracks
Thickness
Process
10-15 µm
Screen printing
 Drying(150 °C)
 Firing (850 °C)
 Copper
17, 35, 70 µm + galvanic
deposition 20-50 µm
Drilling

It is repeated for each layer
Hole Plating (PTH &
Vias)
Photoresist Deposition
Photoresist Exposition
Photoresist Stripping
Galvanic process, Cu Sn/Pb
Etching
Photoresist Tin/Lead Stripping
Solder mask
Finishing
* Double side
12
Main differences between Ceramic Thick Film substrates and PCBs
Characteristics
Hybrid Circuits
PCB
Resistors
Integrated on the substrate
They must be mounted with
SMT process
Max. circuit dimensions
< 100x100 mm
> 200x200 mm
Number of conductive layer
in a multilayer
4-5
> 12
Conductors protection
Overglaze (firing at 600 °C)
Solder mask (epoxy resin)
Humidity absorbing
0
< 0.16 %
Max operating Temperature
(°C)
150 °C
120°C (150°C only with
High Tg PCBS)
Coefficient of thermal
expansion (ppm/°C)
6
12-15 X, Y direction)
70 Z direction
Flexural Strength (GPa)
320
500
Coefficient of elasticity
(E-module) (MPa)
320
25
13
Applications: HVAC

Silicon Pressure Sensor for Domestic Boiler

Why to use a Thick Film circuit:
Harsh environment (temperature + humidity)
Stable and rigid substrate: the die pressure sensor is glued on it, the
Alumina CTE (coefficient of thermal expansion) is lower compared to a PCB
and matches the Silicon CTE


14
Applications: Automotive

Injection control unit
SMT
components



Wire bonded
Chips
4° Conductive
layer
Why to use a Thick Film Multilayer circuit:
Harsh environment (onto the car engine, high temperature, > 100°C)
High integration, signal and power components are assembled and
connected by wire bonding on the same substrate
15
Applications: Medical

Silicon Insulin Micropump for diabetes

Why to use a Thick Film substrate:

Stable and clean substrate, the insulin goes into contact with the ceramic

The total dimensional tolerances are easily obtained and allow a simplified
assembly process of the components
16
Applications: Medical

Heater on sapphire substrate to defog



Why to use a Thick Film substrate:
The 1W heater is screen printed directly on the sapphire
substrate
It is possible to solder the components and a flex on the screen
printed sapphire
17
Applications, Industrial

Inverter 12-38V to control a three-phase motor



Why to use a Thick Film circuit:
High integration, signal and power components are assembled and
connected on the same substrate
The Alumina is a good heat dissipator, in this case 2,5 kW can be
“easily” dissipated
18
Applications: Industrial

MEMS pressure sensor with Temperature sensor for
vacuum equipment



Why to use a Thick Film substrate:
Stable and clean substrate, useful for measuring a vacuum with
precision and reliability
Sharper shape with ceramic, with low tolerance dimensions easily
got
19
Applications: Industrial

Electronics for a capacitive pressure sensor


Why to use a Thick Film substrate:
Temperature stable and with the same CTE (coefficient of
thermal expansion) of the pressure sensor
20
Applications, Industrial

Signal Amplification Hybrid for X-Ray Security Scanner


Why to use a Thick Film substrate:
High value resistors (700 Mohm) with a good precision and
stability with harsh environmental conditions
21
Applications, Appliance

Stainless steal heater (3kWatt) for Dish Washing Machine



Why to use a Thick Film substrate:
The screen printed resistors generate the require power for the
heating
High flexibility with the stainless steel shape that cab be directly
assembled in contact with the fluid to be heated
22
Applications, other MTX "Hybrid" circuits

Chip on Boards (COB) Circuits, generic application



Die Attach, dies from wafer, waffle pack, gel pack
Wire bonding: wedge, ball, Al & Au wire diameter from 17 µm
to 75 µm
Encapsulation: epoxy and silicone glob top
23
Applications, other MTX "Hybrid" circuits

Chip on Flex Circuits, generic application

SMT assembly on very thin flex board (50 µm)

Chip & Wire, special low profile glob top

Flex on Flex Hot bar attach
24
Applications, other MTX "Hybrid" circuits

Chip on Flex Circuits, industrial and medical applications

Wire bonded Hall sensor based Encoders

Wire bonded mems for blood pressure tonometer

Conductibility sensors for medical application
25