Dry Laminasi

Mesin Dry Laminasi : SUPER COMBI 2000

Dry Film Lamination Process: Effects of Lamination Parameters on
Wrinkling and Dimensional Properties of Dry Film and Copper-Clad
Laminate
Edward F. Hagan & Karl H. Dietz
DuPont Photopolymer & Electronic Materials
Research Triangle Park, NC
Abstract
The dry film lamination process involves  adhering a composite structure of  photopolymer and polyester film to a metal-clad dielectric laminate. This paper covers the effects of this process on wrinkles in the dry film resist and on the dimensional stability of clad laminate. Further discussed are the techniques for avoiding wrinkles and dimensional changes while maintaining good conformation and yields.
Introduction
One of the evolutionary developments in dry film photoresist technology in recent years has been a trend to thinner polyester coversheets and thinner photoresist
layers
1. The thinner polyester coversheet enhances conformation in hot roll lamination and results in
improved resolution in proximity printing. The thinner resist layer can also contribute to improved resolution
and better etch uniformity. On the other hand, defect free hot roll lamination of these thinner structures has
become more difficult.
Fig.1 shows the layers of materials the radiation has to pass through in the exposure step and illustrates how the distance between the  phototool and the resist adversely affects resolution due to the presence of non- collimated light or light scatter. Some radiation reaches non-exposure areas where it causes some
degree of polymerization2 . This unintended partial exposure can be minimized by bringing the phototool
in very close contact with the resist, for example through the use of a thin polyester coversheet and a
thin photoresist layer.

Glass or Polyester Frame
Phototool Base
Emulsion Layer
Protection Film
Polyester Cover
Photoresist
Copper
Dielectric
UV-Radiation Energy Distribution in the Resist
Ideal Energy Distribution
Actual
UV-Energy
Resist x-axis

Fig. 1: Exposure Schematic However, these thinner resist architectures will make it more difficult to avoid wrinkling of the resist during lamination. The thickness of the polyester coversheet has been reduced in recent years from 25 microns to about 18 microns. This made the resist more prone to
wrinkles introduced during hot roll lamination, and lamination parameters had to be controlled more
tightly. At 16 microns polyester thickness, a cut sheet laminator needs to be well aligned and tuned to avoid
resist wrinkling. With a 12 microns thick polyester base, we found it impossible to avoid resist wrinkles
on a standard laminator in a lab environment. Photoresist layer thickness has also been reduced in
recent years. The thickness range of commonly used dry film resists is 25-50 microns (1-2 mils). On
average, dry film resist  thicknesses have come downfor print & etch, tent & etch, and pattern plating applications. One major driver has been the need for higher resolution, but productivity through exposure,
development and stripping, as well as reduced processing costs, through waste treatment, also played
a role in this development. Enabling technologies to support this trend are improved electroplating
processes yielding better metal thickness uniformity, and factors contributing to improved conformation of
thinner resists, such as improved laminate quality and resist rheology. The Basics of Lamination: Pressure and
Temperature.
In lamination, good contact between the resist and the substrate surface is achieved by making the resist flow
to conform to the surface topography. Flow is achieved by lowering the resist viscosity through heat, and by
applying a pressure differential for a certain time to cause the flow (see Fig.2 and Table 1). The pressure
may be transmitted to the lamination rolls pneumatically, hydraulically, mechanically, or a combination of these means 3.
stress
shear rate
shear thinning
(pseudoplastic)
Newtonian
Fig. 2: Viscosity/ Pressure Relations
Table 1 -  Actual Lamination Times
Time in nip (secs)
for different speeds and pressures
Speed\Pressure 3 bars 4 bars 5 bars
1 mpm
2 mpm
3 mpm
Figures are for an ASL-24 laminator
0.72 0.82 0.91
0.36 0.41 0.45
0.24 0.27 0.30
The actual force on the resist depends on the design of the roll loading system, taking into account the actual area of the cylinders and the mechanical leverage, if any, of the system. Since the force is applied to the
resist through an elastomeric roll covering (see Fig.3), the deformation of the rubber forms a roll nip contact
zone or “footprint”. The actual pressure (force per unit area) on the resist is dependent on the length and  width of this footprint.
RUBBER
V = V0
µ = 0.5
V < V0
µ = 0.3
STEEL
V << V0
µ = 0
CORK
 V0 = Original Volume   V = Volume Under Pressure      µ = Poisson Ratio
Fig. 3: Volumetric Compressibilities
The footprint is influenced by the total force applied, the roll diameter, and the thickness and  durometer of the roll covering. The pressure across the footprint width varies from zero at the edges to some peak pressure at the center of the nip where the roll covering is compressed the greatest. The average of this
pressure profile (roughly described by a parabola) is about 2/3 of the peak pressure. When referring to nip
pressure, we usually mean this average pressure instead of peak pressure, because it is simpler to determine.
When pressure is transmitted to straight lamination rolls, they tend to bend and form an uneven roll
footprint on the resist (see Fig. 4). The footprint is narrow at the center of the rolls and wider at the ends.
This means that the pressure on the resist at the center is less than at the ends. The result is poorer resist
conformation at the center and a tendency for the dry film to wrinkle (see discussion on wrinkles). Laminator
suppliers are aware of this phenomenon and try to build the rolls as sturdy as is practical. Residual roll
bending can be compensated for 4 with rolls  that are “crowned” (see Fig. 5). A crowned roll has a rubber
covering which is thicker in the center than at the edges and changes gradually from center to edge, resulting in a curved profile.
Low Pressure
Straight Rolls with Roll Bending
Fig. 4: Nip Pressure Profile with Straight RollsUniform Pressure Crowned Rolls Bending Back
 to “Ideal Footprint”
Fig. 5: Nip Pressure Profile with Crowned Rolls In hot roll lamination, the resist is heated to lower its
viscosity so that it can flow and conform to the substrate surface. Heat is applied to the rolls and transferred through the polyester film coversheet and the resist to the resist/copper interface. This is often
supplemented by preheating the boards directly.
 The actual temperature at the resist/copper interface depends on a variety of factors:
·  the contact time of the resist with the heat source,
·  the temperature of the heat source,
·  the heat transfer coefficients of the materials
between the heat source and the resist/copper interface,
·  and the thermal mass and temperature of the board.
The contact time, in turn, is a function of the lamination speed and of the roll/film "footprint" in the lamination roll nip. This time in the nip is only a fraction of a second (see Table 1), and therefore good
resist  flow and flow  volume is needed to conform to the recessed areas of the copper topography. Lamination Wrinkles: Causes and Cures
One advantage of dry-film photoresists is the uniform thickness provided by a carefully controlled coating process. This advantage may be forfeited if the film cannot be laminated without wrinkles. Two different forms of wrinkles can occur:  those which form in the lamination nip, and those which appear some time after
lamination (also known as post-lamination wrinkles).
Both of these wrinkles are closely associated with the polyester base film which supports the  photopolymer
layer but are caused by factors independent of the base
film.
Nip-generated Wrinkles in Cut-Sheet Laminators
The most prevalent and most damaging form of
wrinkles  are nip-generated wrinkles. These are severe
wrinkles, usually causing imaging defects because they
result in creases or folds in the polyester base. These
creases cause off-contact in proximity printing and can
distort the light path (lens effect). The following are
the main sources of these wrinkles; the numbering is
only used to reference the subsequent list of
explanations, not to indicate the severity or frequency
of the event. Note that an ASL-24 cut-sheet laminator
is the basis for the list. Most of the featured sources of
wrinkles will directly apply to all laminators, or can be
related to a generic equivalent on other laminators.
1.  Misalignment between resist supply rolls and
lamination rolls.
2.  Misalignment between  panel input conveyor and
lamination rolls.
3.  Poorly wound, distorted, or cocked polyethylene
take-up rolls.
4.  Uneven drag on film passing over vacuum holding
plate.
5.  Resist rolls not centered on laminator rolls or
panels not centered in rolls.
6.  Distortion of cut sheet edge at trimming.
7.  High electrostatic charge on unwinding film.
8.  Uneven leading edge sealing or tack-down to
panels.
9.  Lamination rolls running at different surface
speeds.
10.  Unequal drag between top and bottom supply roll
brakes.
11.  Worn lamination roll bearings.
12.  Roll bending.
13.  Uneven air cylinder pressures (clamp pressures).
14.  Difference between temperatures of lamination
rolls.
15.  Different rubber compression between top and
bottom lamination rolls.
16.  Non-parallel lamination rolls.
17.  Roll covering (rubber) too thick.
18.  Varying laminate thickness, particularly on
multilayers.
19.  Poorly wound dry film resist.
20.  Non-uniform dry film resist thickness.
The following parameters can aggravate the wrinkling
propensity introduced by the above mentioned causes:
21.  Resist with a thin polyester base.
22.  Wide dry film resist and panels.
23.  Thin resists.
24.  Thin laminate.
Explanation of wrinkle sources for cut-sheet
laminators.
It should be noted that a properly aligned and
maintained laminator is the first step towards wrinkle-
free lamination.Fig. 6: Properly Aligned Laminator
Many of the sources mentioned contribute to wrinkling
problems but may not actually result in wrinkles if the
laminator is adequately aligned and maintained.
Fig. 7: Lamination Wrinkles (possible causes:
Lamination Rolls Closing on Right Side before Left
Side; Closing Force Grater on the Right Side)
 A general rule is that wrinkles, on a reasonably
maintained laminator, are a problem only when
laminating wide (>510mm; >20”) resist or when
laminating very thin (< 0.2mm;<0.008”) laminate.
Source 1. Misalignment between supply rolls and
lamination rolls.
The resist supply rolls are held by roll chucks on the
supply roll shafts. Over-tightening these chucks can
distort the plastic cores of the rolls from round to oval
shape. This can cause an intermittent wrinkling of the
film as it unwinds. While these wrinkles usually “iron
out” on the way to the lamination rolls, they
occasionally make it to the nip or cause drag at the
trim knife, resulting in problems with the next panel.
Another cause of misalignment is a loose or worn shaft
chuck on the supply roll unwind. If there is play
between the clamp and the shaft, the roll of resist will
orbit the centerline at that end of the roll, resulting in
wrinkles which oscillate from one direction to the
other. It can also cause the shaft to jump when the
shaft end drops within the looseness of the chuck. With
a full roll of resist on 150 mm (6”) cores, this can
cause wrinkles which slant one way on  panel and the
other way on the next.
All the idlers between the supply roll and the nip are
important. If an idler is mis-aligned, it can have the
same effect as having the supply roll and the nip rolls
mis-aligned.
Source 2. Misalignment between  panel input
conveyor and lamination rolls.
The panels must be fed with the leading edge parallel
to the lamination rolls. If the input conveyor is angled
to the rolls, the panel will either skew as it first enters
the nip or will begin to rotate as one edge moves closer
to the center while the other edge moves farther from
the center. Distance from center of the two sides is
very important. Because of roll bending, off-center
panels will rotate slightly as they are laminated,
resulting in distortion or wrinkling of the resist. If the
sides of the sheet of cut film are not parallel to the
sides of the panel, adjust the input conveyor until they
are.
Another cause of misalignment occurs principally with
laminators that feature “Thin Panel” and “Thick Panel”
settings, and the “Thin-Panel” setting is mistakenly
chosen for thick panels. When  set for thin panels, the
rolls are closed too tight for the thicker panels and can
cause the panels to skew when they enter the nip.
Source 3.  Poorly wound, distorted, or cocked
polyethylene take-up rolls.
It is advisable to strip off the polyethylene from the
take-up rolls before starting a new roll of resist. Check
that the start of the new polyethylene on the take-up
core is smooth, so the roll remains in contact across the
Resist Roll
Roll Core
Dancer Bar
Vacuum
Plate
Trimmer
Knife
Hot Roll
Board
Resist Roll
Roll Core
Dancer Bar
Vacuum
Plate
Trimmer
Knife
Hot Roll
Boardwhole width of the film. Make sure that the roll is not
cocked on the supply roll that drives it. Remove the
polyethylene any time the polyethylene wrinkles or
folds over.
Source 4.  Uneven drag on film passing over
vacuum holding plate.
The vacuum plate on an ASL-24 keeps the film from
moving during trimming. If the vacuum is not even
across the plate, the film can be displaced such that the
next panel will wrinkle. Plugged or partially plugged
vacuum holes in the plate could be the cause. If the
problem persists after cleaning the holes, clean or
replace the vacuum supply tubing. Volatile
components of the resists will accumulate in them and
reduce the effective vacuum.
Source 5. Resist rolls not centered on laminator
rolls or panels not centered in rolls.
Lamination rolls bend due to the loading on them (see
Fig. 4). This bending tends to drive the edges of the
film faster than the center. If the resist is not centered,
it will feed in faster on one side than on the other,
causing  wrinkles which are angled slightly from the
machine direction.
Source 6. Distortion of cut sheet edge at trimming.
Dull trimmer blades can cause the sheet edge to move
when they cut. The film needs to be held firmly during
trimming, and the blades have to be sharp enough to
avoid dragging the film.  Wrinkles which change
direction each panel can be an indicator of this type of
problem.
Source 7. High electrostatic charge on unwinding
film.
Static charges can cause the film to cling to surfaces
and can cause high separation forces when trying to
remove the polyethylene separator sheet. Relative
humidity below 50% will aggravate this problem.
Ionizing static bars are installed to counteract the
problem, but they need to be maintained clean to be
effective. Additional air ionizers may be required if the
relative humidity is too low. This problem can be
worse on laminators which do not have a seal bar and
which rely on direct roll tacking or sealing of the
leading edge.
Source 8. Uneven leading edge sealing or tack-
down to panels.
Uneven tacking of the leading edge of the resist is the
most likely cause of leading edge wrinkles and of
severe wrinkling in the first half of the panel. The
resist must be uniformly tacked across the whole width
if leading edge wrinkling is to be avoided. The causes
of poor sealing are incorrect seal temperature and worn
seal strips.
The seal temperature can be checked with a contact
thermocouple to ensure the temperature agrees with
the controller gauge. Both the seal tip heater and
thermocouple can be dislodged so that the gauge-
indicated temperature is not the true tip temperature.
Worn seal strips are a frequent cause of poor leading
edge tack. Replace seal strips frequently and check to
make sure the sealing pressure is equal across the
whole width of the panel. Look for “blisters” in the
resist which are actually bubbles of trapped air on the
leading edge of the panel. This is a good indication
that the seal tip pressure is too low and the seal tip
should be replaced. Another indicator of poor sealing
is a crooked leading edge. On an ASL, poor sealing
can be detected by watching the leading edge of the
panel just prior to closure of the laminating rolls onto
the panel.
Source 9. Lamination rolls running at different
surface speeds.
The lamination rolls are geared together to run at the
same angular speed. If the rolls are not the same
diameter, however, the surface speeds will be different.
The difference in surface speeds can cause wrinkling
on thick panels and curling of thin panels. The
diameters themselves are not the only dimensions
determining the surface speed. The diameters of the
underlying steel rolls are equally important. If these
diameters are different, and the outside diameters of
the rubber covering are equal, the roll with the smaller
steel diameter has more rubber than the other roll. The
difference in steel core diameters is caused by the
removal of a small layer of metal each time a roll is
recovered. If the rolls are not kept in pairs, it is
possible to have significantly different diameter rolls
on the laminator together.
This difference will cause a difference in compression
and, in effect, will cause the surface speed to be
different. This will result in more stretch of the
photoresist and polyester base on one side than on the
other. This difference in stretch will result in wrinkles
on rigid panels and may cause curling and post-
lamination wrinkles on flexible substrates.Source 10. Unequal drag between top and bottom
supply roll brakes.
The supply roll brakes should provide enough drag on
the supply rolls to prevent overshooting when the resist
is stopped on the vacuum plate for shearing
(trimming). Unequal drag will cause problems similar
to Source 9 but will not be limited to thick panels.
Source 11. Worn lamination roll bearings.
Worn roll bearings will cause severe wrinkles which
cannot be eliminated. Movement of the roll shaft in
response to loading causes one side to drive faster than
the other, resulting in very long wrinkles at a slight
angle to the machine direction.
Source 12. Roll bending.
Laminator rolls bend when subjected to lamination
loading. The bending causes higher driving speeds at
the edges than in the center of the panel. While it
usually does not affect the panels, except for very thin
laminate, it can drive the resist film in a way that the
film edges tend to move toward the middle, resulting
in lamination wrinkles. If the loading is high enough to
“iron out” the wrinkles during the time the film is
being held by the vacuum bar, the wrinkles may not
appear until the very end of the cut sheet when the film
is dropped by the vacuum bar. At this point there is no
restraint of the trailing edge and the last inch or so is
likely to gather and wrinkle. Frequently, “comet tails”
on tooling holes are caused by a combination of roll
bending and poor control of the resist trailing edge.
Source 13. Uneven air cylinder pressures (clamp
pressures).
The clamp pressures (these are the air cylinders
closing the rolls) must be set at the same pressure for
wrinkle-free lamination. This source may be one of the
biggest causes of long wrinkles starting mostly at the
middle of the panel and moving back at a small angle
to the lamination direction. The gauges are not always
reliable indicators for the actual pressure. A periodic
independent pressure check is advisable.
Source 14. Difference between lamination roll
temperatures.
Differences between the two roll temperatures can
cause different stresses in the polyester base. These, in
turn, will tend to cause wrinkles in panels.
Source 15. Different rubber compression between
top and bottom lamination rolls.
This source of wrinkles can be caused either by
differential speed (Source 9) or by differences in the
hardness of the rubber. Standard silicone rubber
covered rolls are 70  Durometer. Mixing  durometers
can also cause wrinkling problems by changing the
effective speed of the rolls.
Source 16. Non-parallel lamination rolls.
This is a structural problem that can only be solved by
having the machine aligned using alignment templates.
Non-parallel rolls can cause a fluctuating  problem
which sometimes appears on the top of the panel and
sometimes on the bottom side.
Source 17. Roll covering (rubber) too thick.
Rubber roll covering for the ASL-24 is usually about 2
mm (.080”) thick. When rolls are recovered, the
underlying steel core is machined slightly to remove
all the rubber. Since the rolls are machined to the same
outside diameter after recovering, the actual rubber
thickness increases each cycle. Besides the danger of
differential speed (Sources 9, 15) from mixing rolls
with different steel core diameters, there is a problem
with wrinkling associated with thicker rubber covering.
On a continuous (non cut-sheet) laminator, rolls of 2.7
mm (.106”) rubber caused fewer wrinkles than rolls
having 4.0 mm (.157”) of rubber covering.
Source 18. Varying laminate thickness; particularly
on multilayers.
Variable thickness results in panels skewing as they
are laminated which will cause the resist to wrinkle. It
seems to be a bigger problem on  multilayer panels
because of the likelihood of varying thickness. Print-
through of  innerlayers to the outer surface are another
problem source.
Source 19. Poorly wound dry film resist.
Loosely wound resist can create problems because the
drag brake cannot keep uniform drag forces on the roll
of resist. Rolls can telescope during handling if they
are not tightly wound and/or they are stored on end.
This will make them virtually unusable.
Source 20. Non-uniform dry film resist thickness.
Resist which is consistently thicker along one side than
the other will tend to move sideways as it is unwound.This condition can usually be detected by checking for
soft spots when pressing against the surface of the
resist roll. This has been seen on rolls of  resist which
were stored on end instead of the recommended
horizontal position.
Source 21. Thin polyester base.
Wrinkling problems increase inversely to the thickness
of the polyester base. Thinner base has imaging
advantages, but the laminator must be in excellent
condition and well aligned to avoid wrinkling with
such films.
Source 22. Wide dry-film resist and panels.
Films which are greater than 510 mm (20”) wide are
more susceptible to wrinkling than narrower films. At
the limit of the machines, usually  610 mm (24”), the
film is very sensitive to all of the sources of lamination
wrinkles. Roll bending is probably the major cause of
this sensitivity, so wide films almost always require
crowned rolls to minimize wrinkling.
Source 23 Thin resists
The thickness of the resist affects wrinkles. Resists
25µm (1 mil) or less in thickness require higher
pressures to achieve acceptable conformation so roll
bending and other mechanical issues result in more
wrinkling.
Source 24. Thin Laminate
Wrinkling is a serious problem with very thin laminate
under 125µm  (5 mil) core thickness, particularly with
0.5 oz copper. First, the laminate is flimsy, which
makes accurate alignment and panel feeding difficult.
Any misalignment between the film and laminate can
cause not only wrinkling of the film, but distortion and
wrinkling of the laminate itself. Tack uniformity is
crucial, tensions must be controlled carefully to
prevent curling of the resist-laminate package, and
dimensions of the laminator rolls must be identical. An
additional problem is the effect of roll bending, even
with relatively narrow film. The main contact area is
between the rubber rolls outside the width of the
laminate, reducing the actual lamination forces and
causing the resist to bunch together as lamination
occurs. This results frequently in trailing edge wrinkles
which sometimes start as far in as the middle of the
panel. Crowned rolls are a must for thin laminate to
reduce contact between the rolls outside the width of
the laminate.
Post-Lamination Wrinkles
Post lamination wrinkles are rarely visible immediately
after lamination. They are caused by excessive stress
and heat in the polyester support base.  The stresses
placed in the base are relieved by movement of the
base after lamination, sometimes taking days to
equilibrate. The defect looks like furrows or a
washboard, with sinusoidal wrinkles running
lengthwise in the direction of lamination. They are
usually not very pronounced in depth, but can cause
contact problems during exposure and  overplating
problems during plating, if present in  multilayer
outerlayers. Fig. 8 is an exaggerated illustration of this
defect. A 30 micron thick resist might show furrows
with a peak to peak distance of 2 mm and a waviness
of  5-8 microns.
Fig. 8: Post-Lamination Wrinkles (Exaggerated)
The major sources of these wrinkles are:
·  Excessive lamination roll temperatures.
·  Excessive panel preheat.
·  Excessive lamination pressure.
·  Thick dry film resists.
·  Thin polyester base films.
·  Long hold times between lamination and
exposure.
·  Inadequate, i.e. slow cooling of panels after
lamination.
·  Stacking panels after lamination while still hot.
Lamination
(Machine)
DirectionExplanation of post-lamination (PL) wrinkle
sources for cut-sheet laminators.
Source P1. Excessive lamination roll temperatures.
The rolls contact the dry film support base directly as
it enters the nip. If this temperature is greater than 125
degrees C, it may cause PL wrinkles. Whether they
form or not is dependent on how many of the other
sources are present.
Source P2. Excessive panel preheat.
This is unlikely to cause a problem with thin innerlayer
laminate, but is a serious source of problems in
multilayer panels because the amount of heat contained
in the panel itself is sufficient to keep the resist layer
hot for a considerable length of time. While the resist
is hot, it flows easily, providing very little resistance to
movement of the polyester base as it attempts to
reduce the stresses induced during lamination. To
minimize the effects of preheating on PL wrinkles, the
total amount of preheat should be limited. To do so
without adversely affecting lamination, the preheating
should be done as close to the laminator as possible to
ensure the surface (and not the bulk) of the laminate is
still hot.
Source P3. Excessive lamination pressure.
PL wrinkles are caused by heat  and stress in the
polyester base. While the need for good conformation
requires as high a lamination pressure as possible, this
pressure can add to the stress in the base. It would be
better to use two nips set at medium pressures and
temperatures than one nip at high pressure and high
temperature if PL wrinkles are a problem. The second
nip should be directly after the first one to minimize
heat loss between nips. Note that this arrangement
would be more useful on  multilayer panels than on
innerlayers.
Source P4. Thick dry film resists.
PL wrinkles are formed by the buckling of the
polyester cover film as it tries to grow back to its
original width. During lamination it is stretched in the
machine direction and narrowed in the transverse
direction. After lamination the film attempts to return
to its original shape. Since it is connected to the
laminate by the resist layer, it must buckle into a
sinusoidal wave pattern. This means that some of the
photopolymer is thinned out where the wave is
depressed and thickened where the wave is elevated.
When the resist is thin, 37µm (1.5 mil) or less, the
movement occurs very slowly or not at all. With thick
resists the movement is easier since the resist can flow
more readily. Because of this, PL wrinkles, unlike nip-
generated wrinkles,  occur more with thick dry film
resists than with thin resists.
Source P5. Thin polyester base films.
Thick polyester base cannot be stretched as much as
thin base and it cannot buckle easily. Thus thick base
films will not be as susceptible to PL wrinkles as thin
base films. As needs for finer resolution demand
thinner bases, the problem will become more of an
issue.
Source P6. Long hold times between lamination
and exposure.
PL wrinkles take time to form. If a high-count
multilayer panel contains a lot of heat when it is
laminated, and is left to relax a long time before
exposure, the severity of the PL wrinkles will increase.
Source P7. Inadequate (slow) cooling of panels
after lamination.
The panels should be cooled as quickly as possible
after lamination to slow down the flow of the resist
under the polyester base. However, the resist on  a
panel with excessive heat inside will continue to flow
until all the heat has been removed. Thus, cooling only
helps when the bulk of the photopolymer layer can be
dropped quickly to room temperature.
Source P8. Stacking panels after lamination while
still hot.
This is mentioned only because a stack of multilayer
panels containing heat will stay warm for a long time.
There are sufficient reasons to avoid stacking aside
from PL wrinkles to always avoid the practice.
Wrinkling with continuous (non-sheet) laminators.
Continuous laminators, commonly called hot-roll
laminators, have no trimming mechanism and are
considerably less complicated than cut-sheet
laminators. Wrinkling occurs with these machines as
well and many of the sources of wrinkles for cut-sheet
laminators apply to hot-roll laminators. Since these
laminators are frequently used to laminate on one side
of a panel only, using a carrier web to support the
panel and keep resist from contacting the opposing
lamination roll, some additional sources are possible.The use of a wide web of polyester film under the
panel can aggravate wrinkling because the main
driving force is through the web instead of through the
panel. This will accentuate roll bending problems. It is
best to keep the width of the support web slightly
smaller than the width of the panels, and only slightly
wider than the width of the resist.
Hot-roll laminators are not as rigidly built as cut-sheet
laminators and the rolls are more flexible, so roll
bending can be a bigger problem with such machines.
Crowned rolls are probably a must as well as steel
lamination rolls in place of the less rigid aluminum
rolls. If laminating very smooth laminate, particularly
non-woven materials, a harder rubber covering of
about 80  durometer in place of the normal 70
durometer should help.
Summary
Thinner dry film  photoresist constructions, notably
thinner polyester cover foils, have contributed to the
advancement of resist resolution, conformation,
processing speed, cost and waste reduction. However,
these thin films are more prone to wrinkling in the hot
roll lamination process.  Automatic sheet laminators
need to be finely adjusted and maintained to minimize
sources leading to film wrinkles in the lamination nip
such as misalignments, uneven nip pressure, and
uneven film web drag, Temperature profiles during
board preheat, lamination, and post-lamination hold
may have to be adjusted to avoid post-lamination
wrinkles.
                                               
References
1
 Trends in Photoresist Technology, K. Dietz,
European PCB Convention, Wiesbaden, Germany,
Sept. 29- Oct. 1, 1998, Proceedings 1.2
2
 Off-Contact Exposure Sensitivity Test for Dry Film
Resist, Gary  Briney, Sidney Cox, William  Pangratz,
Technical Paper S5-8, Proceedings, IPC Expo, March 9-
13, 1997, San Jose, CA
3
 The Role of Dry-Film Lamination in the Making of
Ultra-Fine Pitch PC Boards, Edward Hagan, Technical
Paper S12-4, Proceedings, Printed Circuits  Expo ’98,
Long Beach, CA, April 26-30, 1998
4
 Using Crowned Rolls to Compensate for Roll Bending,
E. F. Hagan, Technical Bulletin TB-9739 Rev. 1.0 (7/97),
DuPont Photopolymer & Electronic Materials
                                                                       
Acknowledgments:
Contributions to this paper by our colleagues are
gratefully acknowledged. Our special thanks go to:
Byung  Kwan Lee,  Hidehiro Yamada, L. C. Chen,
William L Wilson, Charles Wu, K. T. Sia, S. G. Yu,
Tom Poole, Geoff Heys, Seng Wui Lim, Mats Ehlin,
Jim  Hollerup, Shinji  Yu, G.  Regenauer, John  Raine,
Dick Olson, and G. Sidney Cox.