Description of Task:

Oil drilling reaches
usually a depth of 2 to 3 km. The drill heads containing a sophisticated sensor
electronic, which is collecting data permanently during the drilling process.
Due to the friction temperature up to 300? may occur, only selected electronic
components may resist for a limited time. The circuit board (PCB) cannot be
made of brittle ceramic materials, because of the heavy vibrations are molded,
to protect them against vibrations and ambient influences. Find, compare and
evaluate materials and technologies for the printed circuit substrate
encapsulating materials, to ensuring the function for a limited time.

Problems in oil drilling:

·      
Due to high temperature and pressure normal Ceramic brittle
PCB cannot withstand that much of temperature.

·      
Because of the high vibration PCB may physically damage.

·      
It may affected from chemical resistance

·      
It lowers mechanical work ability and life span of PCB.

Solutions of problems:

             In market there are
various solutions for this problems is available, which are listed below:

·      
Thick film technology

·      
Thin film technology

·      
Direct copper bonded technology

Materials which are used
for above listed technologies are listed here:

·      
Alumina (Al2o3)

·      
Aluminum Nitride (AIN)

 

 

·      
Beryllium oxide (BeO), which is very toxic and dangerous for
human so to use this technology, we must take care of hazardous effect of this
materials.          

Definitions of various technologies:

Thick
film technology:

The “Thick
Film” refers to the thickness of conductor layer on Ceramic PCB. Normally
the thickness will be at least exceeds 10 micron (um), around 10~13um, more
thick than spurting technology in Thin Film Ceramic PCB. Of course thickness is
less than DCB ceramic board or FR4 board.

At the same time, using
thick film technology, we can put resistor, electric capacity, conductor,
semi-conductor, and interchangeable conductor on ceramic board, after
manufacturing steps of printing and high temperature sintering. We can make all
the resistors with the same value, or different value for different resistor on
the same board.

Thin film
technology:

The “Thin
Film” refers to the thinner thickness of conductor layer on Ceramic PCB,
comparing with “Thick film PCB”. Normally the thickness of thin film Ceramic
PCB will be less than 10 micron (10 um). That thin film was parting on ceramic
substrate/core.

In the same substrate
using evaporation, sputtering, electroplating process, and other thin film
manufacturing technology to produce passive network, and assemble on
micro-components, devices separately, plus the hybrid integrated circuit formed
by packaging.

According to the
components parameters concentration and distribution situation in passive
network, thin film ceramic PCB is divided into lumped parameter and distributed
parame-

 

 

ter. The former applies
to low-frequency to microwave band, and later only applies to the microwave
band.

Direct
copper bond technology (DCB):

DCB (Direct Copper Bonded) sometimes
also named as DBC (Direct Bonded Copper) technology denotes a special process
in which the copper foil and the Al2O3 or AIN (one or
both sides) are directly bonded under appropriate high temperature.

The super-thin DCB substrate has
excellent electrical isolation, high thermal conductivity, fine solder ability
and high bonding strength. It can be etched like normal FR4 PCB, but has a high
current loading capability. Therefore DCB ceramic PCB has become the base
materials of construction and interconnection technology of high power
semiconductor electronic circuits and also have been the basis for the
“Chip On Board” (COB) technology which represent the packaging trend
in the future.

Importance of PCB(Film technology) compare to MCPCB (multilayer):

Apart from MCPCB if we want to use PCB
in high pressure, high insulation, high frequency, high temperature, and high
reliable and minor volume electronic products, then Ceramic PCB will be our
best choice.

Why Ceramic PCB has such excellent
performance? we can have a brief view on its basic structure and then we will
understand.

96% or 98% Alumina (Al2O3),
Aluminum Nitride (AIN), or Beryllium Oxide (BeO).

 

 

Conductors material: For thin,
thick film technology, it’ll be silver palladium (AgPd), gold palladium
(AuPd); For DCB (Direct Copper Bonded) it’ll be copper only. Thermal conductivity value:
24W~28W/m-K (Al2O3); 150W~240W/m-K for AIN , 220~250W/m-K for BeO; Max compression strength:
>7,000 N/cm2 Application temperature 55? – 850?Breakdown Voltage (KV/mm):
15/20/28 for 0.25mm/0.63mm/1.0mm respectivelyThermal expansion
coefficient(ppm/K): 7.4 (under 50~200C)

Applications of PCB (by using above technologies):

Oil drilling technologyHigh-accuracy clock oscillator,
voltage controlled oscillator (VCXO), temperature compensated crystal
oscillators (TCXOs), oven controlled crystal oscillators (OCXOs);Electric power electronic
control module;Power hybridIndustrial electronic componentHigh insulation & high
pressure device;High temperature (up to 800C) High power LEDHigh Power semiconductor modulesSolid state relay (SSR)DC-DC module power sourcesUnder water off-shore
applicationsElectric power transmitter
modules Solar-panel arrays

 

Comparisons of various technologies:

 

Parameters

Thick film technology

Thin film technology

Direct copper bonded technology (DCB)

Thickness of conductor layer

0.01(mm)
– 0.02(mm)

Less
than 0.01 (mm)

0.1(mm)
– 0.3(mm)

Temperature range

Up
to 500?

Lower
than Thick film

55?
– 850?

Cost (for same stack up)

Lower
than DCB

Lower
than Thick film

Highest

Conducting material

Silver palladium, gold palladium, Mo/ Mu + Ni

Same as thick film

Al2O3, AIN

Applications

Oil
drilling, high power LED,ensor
 
 
 
 

Solar
cell, Injection system, Automotive light system
 

Industrial
electronics, Power hybrids, Solid-state relays

Parameters of designing PCB:

Thick film technology:

 

·       
Substrate can be 96% or 98% Alumina
(Al2O3) or Beryllium Oxide (BeO), thickness range: 0.25, 0.38, 0.50mm,
0.635mm (default thickness), 0.76mm, 1.0mm. Thicker thickness such as 1.6mm
or 2.0mm can be customized too.
·       
Conductor layer material is silver
palladium, gold palladium, or Mo/Mu+Ni (for Ozone);
·       
Thickness of conductor >= 10 micron
(um), and Max can be 20 micron (0.02mm)
·       
Min trace width and space for volume
production: 0.30mm & 0.30mm, 0.20mm/0.20mm is also okay but cost will be
higher, and 0.15mm/0.20mm only available for prototype.
·       
Tolerance for final trace layout will
be +/-10%
·       
Both gold and silver palladium is
workable for gold-wire bonding, but customer need to mention that so that we
will use special silver palladium which is suitable for that artwork.
·       
Gold palladium is much more expensive
than silver, about 10~20 times higher
·       
More different resistor value on the
same board, more expensive board will be
·       
Normally layers are 1L and 2L (with
plated through hole (PTH), and plated material is the same like the one used
for conductor), and maximum layers can be 10 layers
·       
Only board with Rectangle shape can be
shipped via single piece, or via panel
·       
Solder mask is also available upon
request, working temperature >500 C, and color is semi-transparent.
·       
For same stack up, cost lower than DCB,
higher than MCPCB
 

Thin
film technology:

·      
Compared to thick-film ceramic PCB,
the major characteristics of thin-film circuits is the smaller size.
However, the manufacturing equipment used is more expensive and the cost of
production is higher.
 
·      
Thin-film Ceramic PCB is suitable
for a variety of circuits, especially for analog circuit which need high
accuracy, great stability, and excellent performance. Compared with other
circuit’s board, it is more suitable for microwave circuits.
·      
There’re a number of ways to produce
thin film layer, such as the normal physical vapor deposition (PVD), and
less popular anodic oxidation or electroplating.
·      
 In the physical vapor deposition (PVD)
method, the most commonly used are evaporation process and the sputtering
process.
·      
Both two processes are carried out
in a vacuum chamber, therefore, so they are called by a joint name as
“vacuum film-forming method”. Using these two methods, passive components,
interconnects trace, insulation film and protective film can be produced in
passive network.
·      
Interconnects trace, insulation film
and protective film can be produced in passive network.
·      
In manufacturing microwave hybrid
integrated circuits, electroplating method can be used to increase the
thickness of thin-film micro-strip line, in order to reduce power
consumption.
·      
Using anodic oxidation method, a
dielectric film can be produced and resistance value of film resistor can
be adjusted.
Direct
copper bonded technology (DCB):

·      
High mechanical strength,
mechanically stable shapes. High strength, fine thermal conductivity,
excellent electrical isolation. Good adhesion, corrosion resistant;
·      
Excellent thermal cycling
capabilities (up to 50,000 cycles), high reliability;
·      
No contamination, free of
environmental problem;
·      
Wide application temperature:
-55C~850C. The thermal expansion coefficient is closed to that of
silicon, simplify the production technology of power module.
·      
 Compared to thin or thick film ceramic
board, DCB has much thicker conductor (copper) which thickness will be
0.1mm~0.3mm. Here are more advantage to use DCB Ceramic printed circuit
board.
Design of Thick film technology in details:
·      
Conductive, resistive and
dielectric films are selectively deposited by screen printing on ceramic
substrates,
·      
Mostly on 96 % alumina substrates.
These films are dried and fired. They are of a fired thickness between 5
to 20?m in one print according to the type of the paste used.
·      
If there is a requirement for
thicker films it is necessary to use either special pastes or to print
several times. The films are generally fired at temperatures higher than
500 °C.
 
Standard substrate -alumina ceramic (Al2O3 ):
·      
It is chemically resistant printed
film pattern carrier that is resistant to high temperatures.
·      
It is outstanding electrical
insulator and thermal conductor as well. It uses 96 % alumina ceramics
made by own company process.
·      
It is also possible to provide
other ceramic materials, e.g. alumina 99 %, AlN or ZrO2.
 
Printed substrates:
·      
This is usually a ceramic
substrate printed with conductive, dielectric or resistive films. Maximum
external substrate dimensions of are 200 by 200 mm, thickness can vary
between 0.1 mm and 1 mm.
 
·      
The substrates can be printed on
one or on both sides. The patterns on both sides can be connected by metallized
through-holes.
·      
Each substrate side can be
provided with more film levels (one-sided or double-sided multilayer film
structure).
 
Screen printing:
·      
Technological process where
conductive, resistive and dielectric pastes are applied using screen
masks.
·      
The screen is made mostly of a
stainless mesh. In some cases printing stencils made of thin stainless
sheet are used.
 
Screen:
·      
A stainless mesh mask is fixed in
a metallic frame. The mesh mask is photo-processed using a light
sensitive emulsion.
·      
The emulsion covers openings in
the mesh and thus it masks the part of the substrate that should not be covered
by the paste.
·      
Open part of the meshes allows the
paste deposition. For each film pattern deposition one screen is needed.
 
Thick film resistor:
·      
Resistors are made by resistive
paste printing, drying and firing. The resistance of a resistor is set by
its dimensions and the paste type.
 
 
Resistor trimming:
·      
The precise resistance value is
set by laser trimming. The resistor geometry is modified by sophisticated
cuts.
·      
It is possible to attain precision
of 0.5 % or better from nominal value of the resistor’s resistance.
 
CO2 laser:
·      
Laser system designed for
machining fired alumina substrates (scribing, cutting and drilling). This
procedure enables cutting out almost any pattern needed.

When designing the
printed substrate customer should specify:

 

1.    
External dimensions of the substrate,
other important dimensions and their tolerances.

2.    
Number and material of the films for the
TOP and the BOTTOM side, minimum line width.

3.    
Geometry of resistors, nominal resistor
resistance, tolerance of this value, nominal power load of this resistor.

4.    
Surface treatment of the printed
substrate: passivation, tinning and pads solder ability, size of the pads for
wire bonding, etc.

5.    
Screens and printing templates
production, working out programs, production data.

6.    
Special customer requirements.

Conclusion:

Many PCB technologies available on the
market, along with their individual benefits and disadvantages, are suitable
for its applications.          

            As discussed above problem of oil
drilling and its solution, we can conclude that:

·      
By using PCB with special type of technology such as thick
film technology, thin film technology and direct copper bonded technology
(DCB), we can get more advantages than Multilayer PCB.

·      
Advantages like temperature limit up to 850?, also it can
give protect to vibration (no breakdown of PCB), more life span, avoid problems
of corrosion etc.

 

·      
Cost of this film technology is also economically good and
accordingly application we can design thickness of conducting material and
price can be also vary according to applications.

Nevertheless, all PCB types have their
benefits, and which is best depends on the respective application with
individual requirements and conditions. Since PCB design, construction and
material are essential for optimized thermal designs, it is therefore
recommended to verify the total system.

 

Hence, by using film
technology we can overcome problem arises to PCB due to high temperature while
oil drilling.