Multilayer Printed Circuit Board PCB Prototypes Metal Core Stack-up
Brand Name:Linked Electronics
Certification:UL, TS16949, ISO14001, ISO9001
Model Number:LPCB1501
Minimum Order Quantity:1pcs
Delivery Time:2 days
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Multilayer PCB Stack-Up Design & its Lamination Process
Multilayer PCB or multilayer printed circuit boards are circuit
boards which is composed of three layers or three more conductive
layers (copper layers). The copper layer is pressed together by the
resin which is normally called as prepreg. Due to the complexity of
the multilayer PCB manufacturing process, high x-out rate, and
difficulty in PCB rework. Thus, the cost of multilayer PCBs is
relatively higher than a single sided PCB and two-layer PCB.
Linked Electronics manufactures multilayer PCB up to 56 Layer, from
FR4 material, high frequency material or mixed-press materials:
Fr4, Rogers, Polyamide, metal core PCBs.
Multilayer PCB Manufacturing
This page will illustrate more information about multilayer PCB.
Also this will provide you a guidance into the Multilayer PCB
solutions.
What is the definition of Multilayer PCB printed circuit board?
Multilayer PCB can be referred to as a multi-layer printed circuit
board that is composed of three or more layers. This is made up of
a substrate layer, which has a conductive metal on top and bottom
sides. It also offers enhanced functionality. They are utilized in
complex devices which require a very high number of connections.
Multilayer PCB boards includes at least three layers of conductive
layers. This multilayer PCB laminating process means pressing FR4
core and PP together.
Both of them are laminated under high hydraulic press pressure and
temperature condition. This process will melt prepreg which later
make the prepreg to join these layers together.
Multilayer PCB Manufacturing Steps
The manufacturing process of multilayer circuits takes several
complicated steps which much more difficult and complex than
doubled sided PCBs.
PCB Layout
Printed Circuit boards should be rigorously compatible with, a PCB
layout created by the engineer designer using PCB design software.
Here is some of the commonly-used PCB EDA software, Altium
Designer, OrCAD, Pads, KiCad, Eagle etc. NOTE: Before the PCB
fabrication, designers should inform their contract manufacturer
about the PCB design software version used to design the circuit
since it helps avoid issues caused by discrepancies.
Once the PCB design is approved for production, designers export
the design into format that PCB manufacture accepts and the
frequently used program is called extended Gerber in the format
IX274X.
The PCB industry birthed extended Gerber as the perfect output
format. Different PCB design software possibly calls for different
Gerber file generation steps, they all encode comprehensive vital
information including copper tracking layers, drill drawing,
apertures, component notations and other options. All aspects of
the PCB design undergo checks at this point. The software performs
oversight algorithms on the design to ensure that no errors go
undetected. Designers also examine the plan with regard to elements
relating to track width, board edge spacing, trace and hole spacing
and hole size.
After a thorough examination, designers forward PCB file to PC
Board Houses for production. To ensure the design fulfills
requirements for the minimum tolerances during manufacturing
process, almost all PCB Fab Houses run Design for Manufacture (DFM)
check before printed circuit board fabrication.
Printing of the PCB Design
PCB printing begins after designers output the PCB schematic files
and manufacturers conduct a DFM check. The PCB manufacturers use a
printer called a plotter, which makes photo films of the PCBs, to
print circuit boards. PCB manufacturers will use the films to image
the PCBs. Although it's a laser printer, it isn't a standard laser
jet printer. Plotters use incredibly precise printing technology to
provide a highly detailed film of the PCB design.
The final product results in a plastic sheet with a photo negative
of the PCB in black ink. For the inner layers of PCB, black ink
represents the conductive copper parts of the PCB. The remaining
clear portion of the image denotes the areas of non-conductive
material. The outer layers follow the opposite pattern: clear for
copper, but black refers to the area that'll be etched away. The
plotter automatically develops the film, and the film is securely
stored to prevent any unwanted contact.
Each layer of PCB and solder mask receives its own clear and black
film sheet. In total, a two-layer PCB needs four sheets: two for
the layers and two for the solder mask. Significantly, all the
films have to correspond perfectly to each other. When used in
harmony, they map out the PCB alignment.
To achieve accurate alignment of all films, registration holes
should be punched through all films. The exactness of the hole
occurs by adjusting the table on which the film sits. When the tiny
calibrations of the table lead to an optimal match, the hole is
punched. The holes will fit into the registration pins in the next
step of the imaging process.
Print the Copper Utilized for the Interior Layer
This step is the first while making the inner layer of the PCB. You
print the multilayer PCB design; then copper is re-bonded to the
FR4 or PP that serves as the PCB structure.
Discard unwanted copper
With the photo resist removed and the hardened resist covering the
copper that needs to be kept, the board manufacturing steps into
the next stage: unwanted copper removal. Just as the alkaline
solution removed the resist, a more powerful chemical preparation
wash away the excess copper. The copper solvent solution bath
removes all of the exposed copper. Meanwhile, the desired copper
remains fully protected beneath the hardened layer of photo resist.
Not all copper boards are created equal. Some heavy copper boards
require larger amounts of copper solvent and varying lengths of
exposure. As a side note, heavier copper boards require additional
attention for track spacing. Most standard PCBs rely on similar
specification.
Now that the solvent removed the unwanted copper, the hardened
resist protecting the preferred copper needs washing off. Another
solvent accomplishes this task. The board now glistens with only
the copper substrate necessary for the PCB.
Lamination of the PCB Layers
AOI will be performed to check that there will be zero defects for
the traces. Those can be bonded together. You can achieve this
process in two spes, which includes the lay-up and the laminating.
The entire operation undergoes an automatic routine run by the
bonding press computer. The computer orchestrates the process of
heating up the stack, the point in which to apply pressure, and
when to allow the stack to cool at a controlled rate.
Drilling
Before you drill, the drill spot is located with an x-ray machine.
This helps in securing the PCB stack.
PCB Plating
This process helps in fusing the different PCB layers making use of
a chemical.
Imaging and Plating of the Outer Layer
By doing this you are guarding the copper found on the outer layer
by applying the photoresist.
Final Etching
To protect the copper during the process, a tin guard is utilized.
This gets rid of unwanted copper. This also ensures properly
established PCB connections.
Applying Solder Mask
After cleaning the PCB panels, soldermask is applied onto both
sides of the PCBs
Silk print is printed onto the PCBs
The nearly completed board receives ink-jet writing on its surface,
used to indicate all vital information pertaining to the PCB. The
PCB finally passes onto the last coating and curing stage.
Electrical and Testing Reliability
A technician performs electrical tests on the PCB. The automated
procedure confirms the functionality of the PCB and its conformity
to the original design. At linked electronics, we offer an advanced
version of electrical testing called Flying Probe Testing, which
depends on moving probes onto the pads to test electrical
performance of each net on a bare printed circuit board. Another
advanced testing is fixture which is faster but expensive for
prototypes. The pins of the fixture will touch the pads and check
the conformity of the boards.
Mechanic Process
PCBs will be routed as per customer’s mechanic file after flying
probe test. For PCB using fixture test, the PCB will be routed out
before mechanic process.
FQC
Final inspection will be performed. This includes board thickness,
board warp and twist, any scratches etc. The errors rectified
before it is sent for delivery.
Materials Used in the Manufacturing of Multilayer PCB
The different materials utilized in manufacturing multilayer PCBs
are boards, copper foil, resin system, substrate, infused
fiberglass sheet. Using an alternating sandwich, you can laminate
these materials together.
All the planes of copper are etched and the plating through of all
internal vias is done before the layers.
Multilayer PCB: Advantages
Multilayer PCBs come with lots of great benefits. Some of them
include:
• Higher assembly density
• Provision of high speed and high capacity, as a result of their
electrical properties
• Weight reduction of devices
• Elimination of connectors needed for multiple separate PCBs,
thereby simplifying its construction.
Multilayer PCB: Product Use
Multilayer PCBs can be used in many areas
They are used in manufacturing CAT scan, heart monitors, and modern
x-ray equipment.
• Utilized in the production of high-speed circuits due to their
functionality and durability
• Used for headlight switches and onboard computers due to their
high functionality and heat resistant ability
• The running of machinery and industrial control system utilize
them due to their small size and durability.
• Consumer electronics such as microwaves and smartphones also make
use of multilayer PCBs as a result of their small size and
functionality.
• Satellite applications, GPS, and signal information, also make
use of multilayer PCBs
• Used in the production of computer electronics that are utilized
in motherboard servers due to its performance and space-saving
attributes.
Identifying a Multilayer PCB
You can identify a multilayer PCB through the following
• How your electronic equipment operates briskly, as well as the
ultimate board’s operational setting
• The configuration, layer count, and the value of the board’s
building also play a role in the identification
• The board routing density
• The operating capacity, speed, parameters, and functionality,
distinguishes if the PCB is a multilayer one
• They make use of simple production techniques, but still focusing
on performance and quality.
• Multilayer PCBs are usually difficult to style, in contrast to
single-layer ones that have an easy production process
• Single-layer PCBs are usually produced in large quantities and
can also be ordered in bulk. This helps in reducing the price per
board thereby ensuring that producing these devices are less
expensive. For multilayer PCBs, producing them are usually tedious,
and it may be difficult producing them in large qualities at once.
Components Used in the Construction of Multiple PCBs
The most common parts used the multilayer PCB includes:
• Led
• Capacitor
• Transistor: Utilized in amplifying charge
• Resistors: Control the electric current when it passes through
• Diode: Diodes allow the passing of current through one direction
only
• Battery: provides the circuit its voltage
Why are Multilayer PCBs Usually Widely Used?
Multilayer PCBs are widely used in many areas for the following
reasons:
• Multilayer PCBs are made utilizing high technology. This is why
it is highly trusted due to the skills, processes, and designs
required to manufacture it.
• You can also attribute it to the fact that users always want
something modern.
• Its miniature size gives it its flexibility
• It has a small size, and its performance is enhanced with its
technology. Most users prefer a device having a smaller size
• As a result of its less weight, it is portable enough and
convenient for users. Users can easily carry the around, because
they are not as bulky as some other smartphones.
• Due to its fabrication process, users consider this PCB as one
with high quality
• It makes use of highly skilled professionals, modern technology,
and high-quality materials.
• Easy installation, which makes it widely used, hence there is no
need getting the service outsourced
• Multilayer PCBs come with a protective layer, which prevents
damage from coming to it, as well as an increase in its durability
• It is the most preferred due to its higher density, when compared
to its counterparts. Users love devices that have a higher mass per
volume degree, which should boast enough storage space.
Multilayer PCB Quality Standards
Multilayer PCBs come with some quality standards. They include ISO 9001 makes sure that manufacturers meet the needs of customers
within regulated and permitted requirements that concern a service
or product.
ATF16949 is another quality standard requiring the manufacturers of
electronics to assure the security and quality of automotive
products. This helps in improving the reliability and performance
of automotive components.
The UL listing service requires that manufacturers test their
products thoroughly. This is to makes sure that specific
requirements are met.
Should Multilayer PCBs be regarded as High-frequency PCBs?
Yes, multilayer PCBs are categorized under high-frequency PCBs.
With multiple layers, the boards can have a great thermal
coefficient and impedance control.
To be regarded among the high-frequency design applications, having
a ground plane is very essential. Multilayer applications are
utilized in high-frequency applications like smartphones and
microwaves.
Conclusion
Multilayer PCBs come with lots of benefits and are relevant in
several applications. However, before choosing multilayer PCBs,
there are so many things you need to consider. Make sure that
whatever decision you make suits your needs.
Due to the increase in the packaging density of integrated
circuits, a high concentration of interconnection lines has
resulted, which necessitates the use of multilayer PCB. Unforeseen
design problems such as noise, stray capacitance, and crosstalk
have appeared in the printed circuit layout. Therefore, the printed
circuit board design must minimize the length of signal lines and
avoid parallel routes. Obviously, in the PCB single-sided board,
even the double-sided board, due to the limited number of crosses
circuit that can be achieved, these requirements cannot be
satisfied. In the case of a large number of interconnection and
crossover requirements, the PCB circuit board must be expanded to
more than two layers to achieve satisfactory performance. Thus a
multilayer circuit board has appeared. Therefore, the original
intention of manufacturing multilayer circuit boards is to provide
more freedom in selecting appropriate wiring paths for complex and
noise-sensitive electronic circuits.
Request Multilayer PCB Quote
Contact Us at sales@linked-elec.com
Multilayer PCB circuit boards have at least three conductive
layers, two of which are on the outer surface, and the remaining
layer is integrated into the insulating board. The electrical
connection between them is usually achieved through plated through
holes on the cross-section of the circuit board. Unless specified,
multilayer printed circuit boards are the same as double-sided
boards, generally plated through-hole boards
Advantages and disadvantages of multilayer PCB
Advantages:
1
High assembly density
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2
Small size
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3
Lightweight
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Multilayer PCB circuit boards have at least three conductive
layers, two of which are on the outer surface, and the remaining
layer is integrated into the insulating board. The electrical
connection between them is usually achieved through plated through
holes on the cross-section of the circuit board. Unless specified,
multilayer printed circuit boards are the same as double-sided
boards, generally plated through-hole boards
Disadvantages:
1
High cost
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2
Long manufacturing time
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3
Request high-reliability testing methods.
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Multilayer printed circuit is the product of electronic technology
development in high speed, multi-function, large capacity, and
small volume. With the continuous development of electronic
technology, especially the extensive and in-depth application of
large-scale and very large-scale integrated circuits, multilayer
printed circuits are rapidly developing in the following
directions: high density, high precision, and high layers, tiny
lines and small holes, blind and buried holes, high plate thickness
to aperture ratio and other technologies to meet market needs.
Why are PCB multilayer boards all even-numbered layers?
• It can be manufactured in a PCB factory. The four-layer board
generally uses a core with one copper foil on each sideand a
three-layer board with one copper foil on one side. They must be
pressed together.
• The process cost difference between the two is that the
four-layer board has one more copper foil and bonding layer. The
cost difference is not significant. When the PCB factory makes a
quote, they are generally quoted on an even number basis. Also, 3-4
layers are commonly quoted as a grade. (For example:If you design a
5-layer board, the other party will quote at the price of a 6-layer
board. That is to say, the price you design for 3 layers is the
same as the price you design for 4 layers.)
• In the PCB process technology, the four-layer PCB board is better
controlled than the three-layer board, mainly in terms of symmetry.
The warpage of the four-layer board can be controlled below 0.7%
(IPC600 standard), but the size of the three-layer board is large.
At that time, the warpage will exceed this standard, which will
affect the reliability of the SMT assembly and the entire product.
Therefore, the designer shouldnot design the odd-numbered layer
board. Even if the odd-numbered layer is necessary, it will be
designed as a fake even-numbered layer. That is to design 5 layers
into 6 layersand 7 layers into 8 layers.
Calculation Method of Multilayer PCB Stack-Up:
A: Thickness of inner layer
E: Thickness of inner copper foil
X: Finished board thickness
B: Thickness of PP sheet
F: Thickness of outer copper foil
Y: Finished PCB tolerance
1. Calculate the upper and lower limit of pressing:
Usually tin plate: upper limit -6MIL, lower limit-4MIL Gold plate:
upper limit -5MIL, lower limit -3MIL For example, tin plate: upper
limit=X+Y-6MIL lower limit=X-Y-4MIL Calculate the median = (upper
limit + lower limit)/2 ≈A+the area of the second layer of copper
foil%*E+the area of the third layer of copper foil%*E+B*2+F*2
The inner cutting material of the above conventional four-layer
board is 0.4MM smaller than the finished board, using a single 2116
PP sheet to press. For special inner layer copper thickness and
outer layer copper thickness that more than 1OZ, the copper
thickness should be considered when choosing the inner layer
material.
2. Calculate the Pressing Tolerance:
Upper limit = Finished board thickness + Finished on-line tolerance
value-[Plating copper thickness, green oil character thickness
(Conventional 0.1MM)]-The theoretically calculated thickness after
pressing
Lower limit = finished board thickness-finished product off-line
tolerance value-[electroplating copper thickness, green oil
character thickness
(Regular 0.1MM)]-The theoretically calculated thickness after
pressing
3. Commonly types of PP sheets:
PP KB KB
1080 0.07MM 0.065MM
2116 0.11MM 0.105MM
2116 0.11MM 0.105MM
Generally, do not use two PP sheets with high resin content
together. If the inner layer of copper is too small, please use PP
sheets with high resin content. 1080 PP sheets have the highest
density and low resin content. Do not press single sheets as much
as possible. Only 2 sheets of 2116 and 7630 PP sheets can be
pressed into thick copper plates above 2OZ. The layer cannot be
pressed by a single sheet of PP. 7628 PP sheet can be pressed by a
single sheet, 2 sheets, 3 sheets, or up to 4 sheets.
Explanation of theoretical thickness calculation of multilayer PCB
board after lamination.
Thickness after PP lamination = 100% residual copper lamination
thickness-inner copper thickness*(1-Remaining copper rate%)
4. Typical Recommendation of Multilayer Stack-Up
1): 4 Layer PCB Stack-Up
Previous
Next
2).6 Layer PCB Stack-Up
0.8mm 6 layer PCB stack up
2.0mm 1.6mm 6Layer PCB Stack-up
1.2mm 1.0mm 6 Layer PCB Stackup
0.8mm 6 layer PCB stack up
2.0mm 1.6mm 6Layer PCB Stack-up
3).Typical Stack-Up of 8 Layer PCB
1.2mm 1.0mm 8 Layer PCB Stackup
2.0mm 1.6mm 8 Layer PCB Stackup
1.2mm 1.0mm 8 Layer PCB Stackup
2.0mm 1.6mm 8 Layer PCB Stackup
Introduction to the Multilayer PCB Lamination Process
★ Lamination uses high temperature and high pressure to melt the
prepreg by heat, make it flow, and turn it into a cured sheet. It
is then processing one or more inner etched boards (Black Oxide
Treatment) and copper foil into a multilayer board.
★ This process also includes layer stack-up before lamination,
drill positioning holes, and profile routing after laminated
multilayer boards.
1. Lamination Process Flow
Multilayer PCB Manufacturing Process Steps
Remarks: For 6 layer PCB stack-up and over, two or more inner
layers must be pre-positioned so that the holes and circuits of
different layers have the correct alignment.
2.Position Methods
1) Positioning of rivet nails: press the layout of the inner layer
board and prepreg with pre-drilled positioning holes
1. The sequence is set on the template with rivets and then punched
with a nail punch
2. Rivets to position
2) Solder joint positioning: set the inner layer board and prepreg
with pre-drilled positioning holes according to the layout
1. The sequence is set on the template equipped with positioning
pins, and then through the heating several
2. A fixed point, using the prepreg to melt and solidify when
heated
We are currently using solder joint positioning-RBM
Pre-punched positioning hole for the inner board, the current
method we use is as follows: Punch 4 slot holes on the four sides
of the board, two as a group, respectively locating in the X/Y
direction, one of which is asymmetrical design. The purpose is to
start to prevent a reaction.
A= 7.112±0.0254MM
B= 4.762 ±0.0254MM
Thickness <40mil 40mil<T<60mil >60mil
temperature 300℃ 300℃ 300℃
Time 0.3-0.5min 0.6-0.8min 0.8-1.0min
Quality control after RBM-potential problems
1) Interlayer offset: poor RBM positioning or poor heating point
condensation, causing Shift between layers after pressing, after drilling due to Dislocation of the lines on each layer causes open or short.
Possible reason:
• uInner layer punching deviation
• uThe expansion and contraction of the inner plate is very
different
• uRBM staff deflection
• uRBM parameters do not match-the coagulation effect is not
acceptable
• uRBM heating head wear-bad condensation effect
• u Lay up personnel put the board improperly, causing the heating
point to fall off
2) The inner core is reversed: the order of the inner core is
incorrectly placed during RBM, which affects the quality of the
customer’s assembled board.
Introduction to Layer Stack-Up Process: The layout process arranges
the inner core, prepreg, and copper foil with aluminum plates
according to the structural requirements and reaches the required
height for pressing. CEDAL layer stack-up can be divided into four
main layouts according to the below picture
3).Introduction to Prepreg
A prepreg refers to glass fibers or other fibers impregnated with
resin. After partial polymerization, the resin molecules are
slightly cross-linked, which can be softened by heat. However, it
cannot be completely melted.
Prepreg specifications
Prepreg specifications
Main Performance characteristics of prepreg
Resin content (R/C)
Resin fluidity (R/F)
Gel time (G/T)
Volatile content (V/C)
Test - Resin Content
Resin content (RC)
1). Resin content definition: the percentage of the weight of resin
in the semi-cured to the weight of the prepreg;
2). Calculation formula: RC=(TW-DW)÷TW ×100%;
RC: Resin content; TW: weight of prepreg; DW: weight of glass cloth
after burning.
3) TW can be used as a control indicator when the base weight of
the glass cloth is constant
2. Instrument: Electronic balance, accuracy: 0.001 g
3. Sample: 4 “X 4” X 4 pieces
Description of Resin Content
Resin content of prepreg (RC)
• lRC is mainly related to the thickness of the laminate.
• lThe RC is low,and the thickness of the board is thin;
• lIf the deviation of the left, middle,and right of the RC is
large, the thickness uniformity of the board will be poor.
• After controlling the RC of the prepreg, the required thickness
can be obtained after pressing, and the Cpk value of the thickness
can be increased.
Comparison table of resin content and PP thickness
Thickness calculation after resin filling:
Thickness after PP pressing
1. Thickness = theoretical thickness of single PP-filling loss
2. Filling loss = (1-A side copper residual copper rate) x copper
foil thickness + (1-B side copper residual copper rate) x copper
foil thickness + 0.4*(D2)2*H(inner layer thickness)*N(hole
Number)/the whole board area
The relationship between PP film characteristic parameters and
resin fluidity:
• lThe gel time (PG) is large,and the resin has strong fluidity;
• lThe fluidity (RF) is large, and the resin has strong fluidity;
• lThe minimum viscosity (MV) is small,and the resin has strong
fluidity;
• lLarge flow window (FW), strong resin fluidity;
The influence of resin fluidity on board quality
When PG is long, RF is high, MV is low, or FW is long, the
following situations may occur after pressing:
1. There is a lot of resin flow and poor board thickness uniformity
(easy to be thick in the middle and thin on the edge).
2. White edges appear on the edges of the board due to low resin
content.
3. Skateboarding easily occurs.
4. Easy to show texture.
5. The resin content of the board is reduced, which affects the
dielectric properties and insulation properties. Also,anti-CAF
performance is poor.
6. The internal stress of the plate is increased, and it is easy to
twist and deform after pressing.
When PG is short, RF is low, MV is high, or FW is short, the
following situations may occur after suppression:
1. Dry board, trunk line, dry point.
2. Air bubbles.
3. The cohesive force between core material layers is weakened, and
the board is prone to bursting.
4. The peel strength between resin and copper foil is weakened.
PP storage conditions:
• lStorage temperature: 21±2℃ or below 5℃
• lStorage humidity: below 60%
• lStorage time: 90 days and six month
Key Points of Layer Stack-Up Control
-Placing the Board Along the Laser Beam
Our current lay up is two types. Controlling the consistency of lay
up can ensure uniform force during pressing and avoid white edges
due to loss of pressure. This requires the position of the laser
beam to be adjusted and fixed when preparing for lay up. Laying the
board along with the laser beam in the lay up production.
- Height Control
Controlling the height during lay up can ensure the smooth progress
of pressing and achieve maximum productivity.
Machine Minimum height Highest height
48# 160mm 170mm
73# 220mm 260mm
- Panel Lay Up Requirements
• l Boards of different sizes cannot lay up together.
• lBoards with a difference of more than 15mil in thickness cannot
lay up together.
• lThe boards of different thicknesses are lay up together, the
thermocouple must be placed in the middle of the thin board, and
the ADARA staff shall be notified to increase the curing time by 10
minutes.
• lSmall plates (less than 10 pieces) of different copper foil
thickness can be lay up together by cutting the copper foil, and PE
release film must be placedbetween the board and the conductive
copper foil during production.
- Separate Lay Up Requirements
• Lay up the board in the middle of the whole cycle.
• Add dummy lay up on the top and bottom of the production board
and reach the lowest height.
- Separate Lay Up Requirements
The Black Oxide Treatmentboard is stored in the environment for a
long time, and it is easy to absorb water, causing delamination
after pressing
Process Storage time
B/F 72hours
B/O 24hours
Lay Stack up design guidelines
1. Inner board design requirement
• The edge of the inner board is filled with dummy pads.The pad
diameter is required to be 4.0mm, and the spacing is required to be
1.5mm.
• The two layers of dummy pads corresponding to the inner layer
board mustbe staggered by half the pad distance to balance the
pressure during pressing.
• The dummy pads of adjacent rows should be staggered to improve
flow resin.
In the PCB design, if the removed area by the rout is large, a
dummy pad is required to be added to the rout area to increase the
residual copper rate and reduce the filling. The pad diameter is
required to be 4.0mm, and the spacing is required to be 1.5mm.
When designing in array, if the area removed by rout is relatively
large, add a dummy pad in the routarea to increase the residual
copper rate and reduce the filling. The pad diameter is required to
be 1.5mm, and the spacing is 1.0mm.
• For designswith broken edges, dummy pads must be filled with a
pad diameter of 1.5mm and a spacing of 1.0mm.
• lThe two layers of dummy pads corresponding to the inner layer
board are required to be staggered by half the pad distance to
balance the pressure during pressing
2. PP Design Requirements
1. The centrally symmetric structure can avoid the bending
phenomenon caused by structural stress.
2. High R/C, thin fabric on the outer layer
• lThe same glass cloth combinationand high resin content are
placed on the outer layer.
• lDifferent kinds of glass cloth combinations, based on the
principle of symmetry, thin fabrics are placed on the outer layer.
3. Warp to warp, weft to weft
The glass cloth yarn contains different yarn counts in warp and
weft directions, resulting in different glue content and
differences in thermal expansion in the two directions.
4. Each layer of prepreg has a reasonable thickness
• lThe thickness andglue content is high. The thickness is not
suitable for control
• lSmall thickness, low glue content,and low adhesion
5. Minimum number of layers
• Many layers, high cost, andnot suitable for process control
Pressing Method – Hydraulic Press
The structure of the hydraulic pressing machine is vacuum type and
standard pressure type. The plate between the openings of each
layer is clamped between the upper and lower hot plates. The
pressure is from bottom to top, and the heat is transferred from
both upper and lower hot plates to the plate.
Advantages: simple equipment, low cost, large output.
Disadvantages: large amount of glue flow, poor thickness
uniformity.
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Pressing method - ADARA SYSTEM Cedal
DARA SYSTEM Cedal
The Cedal is a revolutionary laminating machine. Its operating
principle uses continuous coiled copper foil that laminates in a
closed vacuum chamber. Current is then applied at both ends. Due to
its resistance, the copper foil generates high temperature and
heats prepreg, and the pressure is applied by the upper air bag to
achieve the compression effect.
Advantages:
• Using the upper and lower interlayer copper foils for electric
heating, energy-saving,and low operating cost.
• Small temperature difference between the inner and outer layers,
uniform heating, good product quality.
• Cycle time is short, about 60minutes.
• Fast heating rate (35/min).
• Disadvantages:
• The equipment has a complex structure and high cost.
• Single machine output is small.
• The pressure is a pneumatic working method, which cannot provide
high pressure.
Pressure curve
Parameter Control and Function of Pressing
Vacuum:
It can help to remove gases, air, and small monomer residues
generated by solvent volatilization.
Temperature:
The curing agent DICY is very stable at room temperature and can be
cured quickly after the temperature rises. Experiments show that
170°C is the ideal curing temperature. Therefore, it is necessary
to control the temperature above 170°C during the pressing process
to complete the curing reaction.
Heating Rate:
Maintaining a specific heating rate can appropriately increase the
resin’s fluidity, thus improving the resin’s wettability and
preventing problems caused by thermal stress.
Pressure:
Offset the vapor pressure generated by volatiles. Improve resin
fluidity. Increase interlayer adhesion. Prevent deformation due to
thermal stress during cooling
Thickness Control
Thickness test
• Use a thickness gauge to measure the thickness of the four
corners and a midpoint of each plate
• The test point is 50 mm from the edge of the board
• Thickness tolerance: general thickness requirements ± 10%
Current thickness control after pressing
• Use a thickness gauge to measure the thickness of the four
corners and a midpoint of each plate
• The test point is 50 mm from the edge of the board
• Thickness tolerance: general thickness requirements ± 10%
Multilayer PCB is manufactured by stacking two or more circuits on
top of each other, and they have reliable pre-set interconnections.
Since drilling and plating have been completed before all layers
are pressed together, this technique violates the traditional
manufacturing process from the beginning. The two innermost layers
are composed of traditional double panels, while the outer layers
are different. They are composed of single independent panels.
Before pressing, the inner substrate will be drilled, through-hole
plated, pattern transferred, developed, and etched. The outer layer
to be drilled is the signal layer, which is plated through so that
a balanced copper ring is formed on the inner edge of the
through-hole. The layers are then rolled together to form a
multilayer PCB, which can be connected to each other (between
components) using wave soldering.
Pressing may be done in a hydraulic press or an overpressure
chamber (autoclave). In the hydraulic press, the prepared material
(for pressure stacking) is placed under the cold or preheated
pressure (high glass transition temperature material is placed at a
temperature of 170-180°C). The glass transition temperature is the
temperature at which an amorphous polymer (resin) or part of the
amorphous region of a crystalline polymer changes from a hard and
brittle state to a viscous, rubbery state.
Multilayer Circuit Board
1. Autoclave Pressure Cooker
It is a container filled with high-temperature saturated water
vapor, and high-pressure can be applied. The laminated substrate
(laminates) sample can be placed in it for a period of time to
force moisture into the board, and then take out the sample again.
Place it on the surface of high-temperature molten tin and measure
its “delamination resistance” characteristics. This word is also
synonymous with the pressure cooker, which is commonly used by the
industry. In addition, in the multilayer board pressing process,
there is a “cabin press method” with high temperature and
high-pressure carbon dioxide, which is also similar to this type of
Autoclave Press.
2. Cap Lamination Method
It refers to the traditional lamination method of early multilayer
PCB boards. At that time, the “outer layer” of MLB was mostly
laminated and laminated with a single-sided copper thin substrate.
It was not used until the end of 1984 when the output of MLB
significantly increased. The current method is the copper-skin type
large or mass pressing method (Mss Lam). This early MLB pressing
method using a single-sided copper thin substrate is called cap
lamination.
3. Crease Wrinkles
The multilayer board pressing often refers to the wrinkles that
occur when the copper skin is improperly handled. Such shortcomings
are more likely to occur when thin copper skins are below 0.5 oz
and laminated in multiple layers.
4. Dent Depression
It refers to the gentle and uniform sag on the copper surface,
which may be caused by the partial protrusion of the steel plate
used in pressing. If it shows a neat drop of the faulty edge, it is
called “dish down.” If these shortcomings are left on the line
after copper corrosion, the impedance of the high-speed
transmission signal will be unstable, and noise will appear.
Therefore, such a defect should be avoided as much as possible on
the substrate’s copper surface.
5. Caul Plate Partition
When the multilayer board is pressed, in each opening of the press,
there are often many “books” of bulk materials (such as 8-10 sets)
of the board to be pressed. Each set of “bulk materials” (Opening)
Book) must be separated by a flat, smooth, and hardened stainless
steel plate. The mirror stainless steel plate used for this
separation is called “caul plate” or “separate plate.” At present,
AISI 430 or AISI 630 are commonly used.
6. Foil Lamination Method
Refers to the mass-produced multilayer board, the outer layer of
copper foil and film are directly pressed with the inner skin,
which becomes the mass lam of the multilayer board. This replaces
the early traditional single-sided thin substrate Press legal.
7. Kraft Paper
When multilayer boards or substrate boards are laminated, kraft
paper is often used as a heat transfer buffer. It is placed between
the hot plate (Platern) of the laminator and the steel plate to
ease the temperature rise curve closest to the bulk material.
Between multiple substrates or multilayer boards to be pressed. Try
to minimize the temperature difference of each layer of the sheet;
the commonly used specifications are 90 to 150 pounds. Because the
fiber in the paper has been crushed after high temperature and high
pressure, it is no longer tough and difficult to function, so it
must be replaced with a new one. This kind of kraft paper is
co-cooked with a mixture of pinewood and various strong alkalis.
After the volatiles escape and the acid is removed, it is washed
and precipitated. After it becomes pulp, it can be pressed again to
become rough and cheap paper material.
8. Kiss Pressure, Low Pressure
When the multilayer board is pressed and the plates are placed and
positioned, they will start to heat and be lifted by the hottest
layer from the bottom. Afterward, lift with a powerful hydraulic
jack (ram) to press each opening (bulk materials in the opening)
and are bonded together. At this time, the combined film (prepreg)
begins to gradually soften or even flow, so the pressure used for
the top extrusion cannot be too large. This is to avoid slippage of
the sheet or excessive flow of the glue. This lower pressure (15-50
PSI) initially used is called “kiss pressure.” However, when the
resin in the bulk materials of each film is heated to soften and
gel and is about to harden. It is necessary to increase to the full
pressure (300-500 PSI) so that the bulk materials are tightly
combined to form a strong multilayer board.
9. Lay Up stacking
Before pressing multilayer circuit boards or substrates, various
bulk materials such as inner layer boards, films and copper sheets,
steel plates, kraft paper pads, etc., need to be aligned, aligned,
or registered up and down to prepare. Then it can be carefully fed
into the pressing machine for hot pressing. This kind of
preparatory work is called Lay Up. To improve the quality of
multilayer boards, not only this kind of “stacking” work must be
carried out in a clean room with temperature and humidity control,
but also for the speed and quality of mass production. Generally,
the large-scale press method (Mass Lam) in construction, even
“automated” overlapping methods are needed to reduce human error.
To save workshops and shared equipment, most factories combine
“stacking” and “folding boards” into a comprehensive processing
unit, so automation engineering is quite complicated.
10. Mass Lamination (Lamination)
Before pressing multilayer circuit boards or substrates, various
bulk materials such as inner layer boards, films and copper sheets,
steel plates, kraft paper pads, etc., need to be aligned, aligned,
or registered up and down to prepare. Then it can be carefully fed
into the pressing machine for hot pressing. This kind of
preparatory work is called Lay Up. To improve the quality of
multilayer boards, not only this kind of “stacking” work must be
carried out in a clean room with temperature and humidity control,
but also for the speed and quality of mass production. Generally,
the large-scale press method (Mass Lam) in construction, even
“automated” overlapping methods are needed to reduce human error.
To save workshops and shared equipment, most factories combine
“stacking” and “folding boards” into a comprehensive processing
unit, so automation engineering is quite complicated.
Multilayer Printed Circuit Board PCB Prototypes Metal Core Stack-up
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