Note: Descriptions are shown in the official language in which they were submitted.
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S~OFT PACK PACKAGE AND DISPENSING SYSTEM FOR LIQUID
PHOTOIMAGEABLE SOLDER MASK
Background Of The Invent;on
1. Technical Field
The present invention relates to a soft pack package holding components in
separate compartments in the package which components when mixed react to
form a reaction product and to a method for preparing the reaction product and for
dispensing the reaction product to a device and, in particular, to preparing a solder
mask reaction product which is made by mixing at least two reactive components
10 which are held in separate compartments in a partitioned soft package and to
dispensing the solder mask to a screen printer or other apparatus jQ the fabrication
of electronic components such as printed wiring boards.
2. Background Art
Electronic components such as a printed wiring board (PWB) are fabricated
~5 using a substrate material such as a polyimide board, paper-epoxy board, glass-
epoxy board and the like. Other substrates such as silicon semi-conductor wafersare used to make computer chips. Both type substrates require a series of steps to
define and construct a circuit pattern on the substrate and for convenience the
following description will be directed to PWBs. In one fabrication process, a
2û cleaned board having a copper layer thereon (usually on both surfaces) is coated
with a photoresist material which is exposed to define the desired circuit pattern .
The resist is then developed to form the desired copper pattern which remains
covered by the resist. The unwanted copper which is not covered is then etched.
The resist is then etched to expose the desired circuit pattern as bare copper lines
25 on the surface of the board. Boards having through-holes are used for the
formation of two-sided boards. These boards can be laminated together to form
multi-layer PWBs which have a plurality of inter-leaved parallel planar copper and
board layers with the through-holes providing the inter-connections between the
circuit patterns on each board. Other materials are also applied and coated on the
30 boar~:i during the PWB manufacturing process such as a liquid photoimageable
solder mask which is used to protect the circuitry from further fabrication
processing. The above procedure is generally known as a subtractive process.
An additive process starts with a board having no copper foil on its surface
and requires the deposition of a conductor such as copper by for example
35 electroless and electrolytic deposition. After treating the board to promote
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adhesion of the copper to the board, a photoresist layer is employed to define the
desired circuit. After the resist is imaged and developed to expose the desired
circuit pattern, copper is plated on the board to form the circuit. The remaining
resist is then etched leaving a board having the desired circuit pattern thereon.
5 Other PW~ fabrication processes such as the semi-additive process may similarly
be used to make PWBs. U.S. Patent No. 5,358,602 discusses the above processes
in detail and is incorporated herein by reference.
An essential step in the manufacture of PWBs is coating on the board
materials which are formed by reacting two or more components (usually a
0 chemical reaction~ and which have a relatively short pot life and/or work-life and
which must be substantially homogeneous and free from part;culate contaminants.
Coating techniques such as screen printing, curtain coating and spray coating are
used and materials such as plating resists and solder masks are exemplary of these
type coatings. For convenience the following description is directed to solder
15 masks and this term is meant to include photoimageable solder masks.
Basically, a solder resist or solder mask is coated over those areas of the
board to be protected from solder especially when soldering is conducted in masstechniques such as wave soldering or dip soldering where improper soldering and
improper connections can occur. Solder masks may be applied using conventional
screening, exposure, development and convection oven equipment to yield a
solder mask film covering the desired areas of the board. The film is of controlled,
uniform thickness which can withstand the rigors of a soldering operation and/orsolvents, acid or alkaline post-assembly cleaning solutions. The controlled filmthickness over the circuit conductors improves solderability of components, pads25 and through-holes and makes for easier solder paste application and post-assembly
cleaning.
A solder mask is generally a highly resistant material made by reacting two
or more viscous liquid or semi-solid components to form a liquid which is coatedon a board and hardened by imaging to form a resistant film. The solder mask
3f) comprises a principle component such as an epoxide and a hardener component
whkh is reactive with the epoxide to form the solder mask reaction product. The
solder mask product is generally a viscous liquid having a viscosity up to about60,û00 cps or higher at room temperature. The solder mask reaction product, oncemade, hardens by itself into a solid form upon standing and/or exposure to light35 and ~nay have a pot-life of up to about a week in a closed container stored at room
temperature. In general, the two components used to make the solder mask are
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mixed together when the solder mask is ready to be used and is preferably used
within a short period of time after mixing to avoid problems associated with
unwanted hardening of the composition. The components may vary greatly in
consistency (viscosity) ranging from a high viscosity such as a semi-solid like putty
5 to a lower viscous material such as syrup. In many cases the principle component
and the hardener component have greatly different viscosities requiring significant
care in handling, measuring and mixing to form the final reaction product. As can
be appreciated, a solder mask must be homogeneous and substantially free of solid
particles which would interfere with the coating process and resultant PWB
10 product. It is important that the two components be thoroughly mixed as
incomplete mixing will change process latitudes and final solder mask
characteristics. If the solder mask is not substantially homogeneous this can affect
the reliability of the fabrication process and result in defective PWBs.
Presently, the components used to make solder masks are two component
15 epoxy systems and are sold as a two component pre-measured system with each
component stored in a separate substantially rigid container. When ready for use,
the contents of one container is emptied into the other container and the mixture
stirred in the container for a period of time usually at least 5 minutes at 400 to 600
rpm to provide a homogeneous solder mask reaction product. The contents of the
20 container may be poured into the coating device or used with a pumping device in
which the container is placed and the solder mask pumped from the container to acoating de~rice. Conventional ink or solder mask pumps may be used to dispense
the solder mask to a screen printer designed for use with solder mask systems and
can be partnered with a conveyerized oven to provide a fully automatic liquid
?5 photoimageable coating and drying system.
With all the safeguards and automatic equipment however, the reliability of
the process depends to a large part on the skill of the worker preparing the solder
mask product. For example, each component is highly viscous and when one
con ponent is transferred from its container to the other container the worker must
30 caref~lly scrape the container to remove the contents of that container and not
introduce any foreign matter into the mixture. Additionally, both components maycause skin and eye irritation and sensitization and usually have foul odors. In the
time that it takes to empty and scrape the containers and mix the component
mixture the work area may be permeated with an odor which is not only
35 unpleasant, but potentially hazardous. The worker must wear safety gloves and the
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work area requires ventilation to alleviate these problems. Another problem is the
transfer of the solder mask product to a dispensing container for dispensing by
pumping to the application device such as a screen printer unless a special
pumping device as desaibed above is employed. Waste disposal of the remaining
solder mask components and solder mask reaction product is also a serious
concern since each component of the solder mask is generally a hazardous material
and must be disposed of according to specific environmental waste treatment
procedures.
Bearing in mind the problems and deficiencies of the prior art, it is therefore
an object of the present invention to provide a method for preparing a substantially
homogeneous product which is the reaction product of two or more components,
and to a system for dispensing the reaction product, the reaction product being in
parttcular a material used to coat electronic components such as a liquid
,~hotoimageable solder mask.
it is another object of the present invention to provide an apparatus for
preparing and dispensing such a reaction product.
A further object of the invention is to provide a method for coating
electronic components such as PWBs with reaction products such as a solder mask
~y screen printing, curtain coating or spray coating.
It is yet another object of the present invention to providç a partially-mixed
reaction product for use to make a reaction product such as a solder mask used in
the fabrlcation of electronic components such as a PWB.
Another object of the present invention is to provide a single package
container holding reactive components which components have been partially or
completely mixed in the container with the mixture being used in the preparationof the fina~ reaction product such as a solder mask or used directly to fabricate an
electronic component.
Another object of the present invention is to provide a package holding
reactive comp~nents which are used to make a reaction product used to fabricate
3C~ electr{)nic components.
Other o~jects and advantages of the present invention will be readily
apparent from the following description.
3. Disclosure of the Invention
The above and other objects, which will be apparent to those skilled in the
art, ~re achieved in the present invention which is directed in a first aspect to a
method for preparing a substantially homogeneous reaction product and for,
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optionally, dispensing the reaction product to a device, the reaction product
comprising at least two components which when mixed react with each other to
form the reaction product, the method comprising:
holding each of the reactive components in a single soft or pliable or otherwisedeformable container which is partitioned to separate the reactive
components;
removing the partition when the reaction product is to be made and mixing the
components in the container either partially or to a substantially
homogeneous biend ready for use by deforming the container to provide
mixing therein;
transferring the partially-mixed components to a mixing container and
completing the mixing to form a substantially homogeneous reaction
product blend; and, when the blend is desired to be dispensed,
dispensing the homogeneous blend to the device.
For reaction products substantially mixed in the bag and ready for use with
little or no additional mixing, the mixed components may be dispensed
directly to the desired device.
in another aspect, the invention is directed to making electronic components
such as PWBs wherein one or more steps of the PWB manufacturing procedure
20 requires the application of a reaction product as a coating on the PWB. When the
reaction product is a solder mask, e.g., liquid photoimageable solder mask, the
solder mask is prepared as described above and is applied to the circuitry of a PWB
using a coating technique such as screen printing, curtain coating or spray coating.
In a further aspect, the present invention provides a single soft or pliable
25 package holding reactive components in separate compartments of the package in
the amounts needed to make a reaction product such as a solder mask. And
further, the present invention provides a single soft or pliable package in which
reactive components held in separate compartments of the package are partially
mixed in the package to form a partially-mixed reaction, e.g., solder mask, product
30 or mixed in the package to form a substantially homogeneous reaction product
suitable for dispensing to a device such as a screen printer.
In another aspect of the invention, an apparatus is disclosed for preparing a
reaction product such as a solder mask comprising a pliable container means (bag)
holding the reaction components, which components are separated in the
35 container by separating means; mixing means for partially or substantially
completely mixing the components in the bag by deforming the bag (by e.g.,
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kneading~ when the separating means is removed; if the components are only
partially mixed, transferring means for transferring the partially-mixed components
from the container to a second container; and agitating means for forming a
substantially homogeneous blend of the transferred partially-mixed components inthe second container means. The apparatus also may include dispensing means for
dispensing the solder mask to the surface of an electronic component such as a
PWB.
4. Brief Description of the Drawings
The features of the invention are believed to be novel and the elements
10 characteristic of the invention are set forth with particularity in the appended
claims. The figures are for illustration purposes only and are not drawn to scale.
The invention itself, however, both as to organization and method of operation,
may best be understood by reference to the detailed description which follows
taken in conjunction with the accompanying drawings in which:
Fig. 1 is a top elevational view of a package of the present invention.
Fig. 2 is a side plan view of the package of Fig. 1.
Fig. 3 is a side elevational view of the package of Fig. 1 in which the
partition is removed and the contents of the package are partially mixed.
Fig. 4 is a side elevational view of an apparatus of the invention.
Fig. 5 is a partial top plan view of a roller device used for transferring the
contents of a package of the invention.
5. Mode of Carrying Out the Invention
In describing the preferred embodiment of the present invention, reference
will be made herein to Figs. 1 - 5 in which like numerals refer to like features of the
25 invention. Features of the invention are not necessarily shown to scale in the
drawings.
As shown in Fig. 1, a bag 10 which is soft or pliable or otherwise
deformable to allow mixing of the components contained within the bag by
deforming the bag, e.g., by kneading or rolling, has at least two compartments 11
3û and 12 separated by partition 19. Compartment 12 also comprises neck portion13. Components 17 and 18 are shown therein in respective compartments 1 1 and
12 and 13. Separation (partition) of the components may be performed by any
suitable type partition such as a frangible seal within the bag or by an external seal
such as a clamping device 23 which clamps partition rod 19 as shown in Fig. 2.
35 Essen~ally, the rod is placed across the width of the bag and the clamp secures the
bag to the rod forming the partition. It will be understood that each of the
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separated components may contain other ingredients normally used in solder mask
formulations such as solvents, flowing agents, fillers, etc. with the important
consideration being that the reactive components of the reaction product be
separated until it is desired to mix the components and form the reaction product .
5The package 10 is shown having handles 14 and 16 at opposite ends of the
bag, which handles also seal the bag. Both handles preferably have openings 15
and 21 to facilitate positioning the bag for mixing and product transfer steps and for
handling of the bag. The bag is shown having edges 20 which are sealed to definethe bag. Basically, the bag 10 is formed by overlaying two films of plastic or other
10suitable material and joining the edges 20 along the longitudinal axis to form the
bag which will be open at both ends at this point. The bag is then partitioned,
filled and sealed as described herein below. For plastic bags the edges are usually
sealed by heating. The bag package containing the components may be shipped
easily and stored for long periods of time before use. When the reaction product is
5ready to be used, the partition 19 is removed or broken and the components of the
bag mixed in the container 10 to form either a substantially homogeneous reaction
product blend or a partial-mix of the components as shown in Fig. 3. Thus, in Fig.
3 the bag is shown without the partition 19 so that the contents of the bag may be
mixed forming mixture 22 (which is a mixture of components 17 and 18). Number
~024 of Fig. 3 represents the internal part of the bag encompassing compartments 1 1,
12 and neck portion 13. Fig. 2 shows a side view of the package of the invention.
A rod 1~ i5 positioned across the width of the bag and partitions the bag in
conjunction with clamp 23. Mixing of the components may be done manually or
mechanically such as by deforming the bag. In a preferred embodiment, the bag
25package is positioned horizontally and secured at its handles 14 and 16 on a flat
solid surface. A roller apparatus as shown in Fig. 5 is then caused to move over the
bag 10 and applies force to the bag to mix the components therein. Preferably, the
roller device comprises a plurality of wheels or rollers 37 rotably attached to a rod
38 which rs positioned transverse to the longitudinal axis of the bag and which rod
30is moved by a mechanism which travels back and forth over the length of the bag
as shown by the arrows. The mechanism may be weighted or otherwise geared to
provide a desired force on the bag and its contents to partially mix the contents. In
a highly preferred embodiment, a mechanism comprising a plurality of parallel
rods each carrying rotably attached rollers of different diameters or shapes is used
~5to provide deformation of the bag and mixing of the components in all directions
within the bag. Fig. ~ shows a preferred roller device comprising two parallel rods
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38 supporting alternating sized rollers 37 rotably attached thereto. The spacingbetween the rollers may vary with the rollers touching at their hubs providing
satisfactory mixing.. In general, the spacing between rollers will be less than about
1 inch preferably less than 0.5 inch, e.g., 0.25 inch. Roller diameters of 6 and 4
5 inch have been successfully used. As can be seen from Fig. 5 it is preferred for
opposing rollers on each rod 37 to be of different sizes to provide enhanced
mixing.
The bag may be of any size and shape and is generally sized to contain the
stoichiometric amounts of each reaction component needed to make the reaction
10 product in the amount needed by the user. The size of compartments 11 and 12
will vary depending on the amount of each component 17 and 18 needed to make
the reaction product and /or design considerations. For a solder mask product the
total amount held in the bag will usually vary up to about 4 kilograms per bag but
may be higher. For a 4 kilogram product size, the bag is generaily rectangular and
15 has internal dimensions of about 36 inch long and 12 inch wide. When the bag is
filled the bag has a height of about 2 inch. In general the internal dimensions of
the bag may vary in size from about 26 inch to 36 inch long and from about 10
inch to 14 inch wide although larger or smaller sizes may be used depending on
the requirements of the user. The bag can be made of any suitable material inert to
20 the components so as not to affect its properties and having sufficient strength to
withstand shipping and mixing of the components in the bag and is typically a
plastic material such as linear low density polyethylene (~DPE). Sealing of the bag
may be done by melting the edges of the bag using conventional techniques. The
Ibag preferably has tabs (or handles) at each end for sealing of the bag and for25 handling and securing of the bag during mixing and reaction product transfer steps.
The bag is preferably elongated at one end with a neck to facilitate opening the bag
and transferring the mixture from the bag.
It is a preferred feature of the invention that the components of the bag be
partially-mixed in the bag before transfer to a finishing mixing device. The
30 components are usually of a different coior and/or viscosity and it is generally
preferred that the partial mixing provide a mixture where no one component,
especially the more viscous component, be present in clumps or globs within the
mixture. Determination of the extent of mixing may conveniently be done visuallyand it is highly preferred that there be no significant amount of streaks or striations
35 in the mixture but that the mixture appear relatively uniform in color. The time
re~ired to form the partial-mix is usually about 5 to 15 minutes using mechanical
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mixing such as the roller device described above. Hand kneading of the bag for
about 1 to 20 minutes, preferably 5 to 15 minutes, usually provides suitable
partial-mixing of the components in accordance with the invention.
Referring to Fig. 4, the components are partially-mixed in the bag 10 (or
5 even if completely mixed therein), the bag is positioned on pivotal table 28 with
the outlet side of the bag facing hinge 29. Apparatus 25 comprises vertical support
members 26 and 26a fixedly connected to horizontal support members 27 and
transverse support members (not shown) to form a rectangular apparatus with
opposite vertical and horizontal support members (not shown). A table 28 is
10 pivotally connected to the apparatus at hinge 29 to allow movement from a
horizontal position A to a vertical position B. Table 28 is shown being moved from
position A to position ~ or vice versa. The package or bag of the invention is
placed on the table 28 when in the horizontal position A and secured thereto. The
package components at this point could be unmixed, partially-mixed or
15 substantially homogeneous. If the package is unmixed, the components could benow partially or substantially mixed. The apparatus could be extended to providefor a roller assembly as described above to mix the components. After the package
has the desired mixing, the table is moved to position B and secured to member 26
by clamp 30. A squeegee or roller device 31 shown having a roller 32 is supported
20 and moved downward over the package 10 along rail 33 forcing the contents of the
package out of the package into mixing container 35. Agitator 34 provides the
mixing needed to form the desired homogeneous reaction product mixture. The
mixture is then dispensed to a device such as a screen printer using pump 36.
Pump 36 is connected to mixer 35 through line 39 and the reaction product
25 discharged from the pump through line 40. In detail, the bag in the vertical
position B is opened (by, e.g., cutting of the bag neck at edge 20b) and the bagcontents transferred to a mixing device or dispensed. It is preferred that the bag
containing the mixture be secured at its handle 14 and openings 15 to provide a
vertical bag position, the bag opened and the contents of the bag removed from the
30 opening at edge 20b using the squccgcc type device 31 which travels downward
over the bag and squeezes the reaction product out of the opening.
The contents of the bag emptied into the mixing container 35 is further
mixed to provide the desired substantially liquid homogeneous reaction product.
The final product will have a substantially uniform color. Any type mixing device
35 34 such as a propeller type stirrer may be used. Any pump which provides a
mixing effect may in some cases be employed to mix the transferred partially-mixed
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components, especially where the partial-mixing provides a relatively or
substantially homogeneous mixture. The product is then dispensed (e.g., by
pouring or pumping) to a device such as a screen printer for applying the reaction
product to the PWB. The final dispensing may be performed using a device like a
5 pump.
it is an important feature of the invention that the components used to make
the reaction product and or the reaction product may be easily and safely waste
treated and disposed of. For example, unmixed components or mixed components
remaining in the bag after transfer to the finish mixing container or dispensed to a
10 device are cured directly in the bag by heating or other suitable means and the bag
disposed of. It has been found that partial-mixing or complete mixing of the bagcomponents in the bag results in any remaining bag components being easily curedso that curing of the product depleted bag contains no significant hazardous
residue components and the bag may be safely disposed of.
The foilowing example is given for purposes of illustration only and the
present invention is in no way deemed to be as limited thereby.
A bag 10 was made by overlaying two sheets of LLDPE plastic each sheet
having a thickness of about 5 mil. Each sheet has 3 bonded layers comprising 2
LLDPE layers 2 mils thick each and a 1 mil nylon interlayer. Referring to Fig. 1, the
20 overall length of each sheet is about 39 inches and 14 inch wide except for the
neck portion 13. Compartment 1 1 is about 7 inch, compartment 12 about 21 inch,
neck 1 3 about 8 inch and each handle 14 and 16 about 1 .5 inch. The width of the
neck portion at edge 20b is about 3 inch. The plastic was heat sealed along edges
20 forming a seal width of about 1 inch. The bag was then partitioned by rod 19
25 positioned across the width of the bag and rod 19 secured to the bag by clamp 23.
The bag, which is open at both ends, was now filled with the components needed
to make a solder mask product. The epoxy component 17 was added to the bag in
compartment 11 and the bag sealed along edge 20a forming handle 14. The
hardener component was then added to the bag in compartment 12 and neck 13
30 and the bag sealed at edge 20b forming handle 16. In a preferred embodiment, the
handle 16 and neck 13 are rolled up forcing any component 18 in the neck portioninto compartment 12 and clamped at the juncture of compartment 12 and neck 13.
This configuration has been found to facilitate handling, shipping and storage of
the bag. The bag could also be folded about the partition 19 or laid flat for
35 shipment or storage. A solder mask reaction product was then made by removingthe clamp 23 and rod 19 and mixing the components using a device as shown in
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11
Fig. 5 which traveled over the bag and kneaded the bag contents. The bag was
positioned on a flat surface and secured to the surface by the bag handles 14 and
16. The bag contents were partially mixed after about 10 minutes and the bag
contents appeared a mottled green color, component 17 being white and
component 18 being green. The bag was then removed from the mixing device
u and secured in a vertical position by hanging the bag from the handle 14 as shown
in Fig. 4. The neck of the bag was cut at edge 20b and the contents of the bag
removed by squeegee device 31 and transferred to a mixing container 35 in which
the contents were mixed using a propeller stirrer 34 for about 5 minutes. The
solder mask was homogeneous and was substantially uniform in coior and was
dispensed to a screen printing machine and F'WBs coated . Excellent coating and
solder mask properties meeting commercial specifications were obtained.
While the present invention has been particularly described, in conjunction
with a specific preferred embodiment, it is evident that many alternatives,
modifications and variations will be apparent to those skilled in the art in light of
the foregoing description. It is therefore contemplated that the appended claimswill embrace any such alternatives, modifications and variations as falling within
the true scope and spirit of the present invention.
Thus, having described the invention, what is claimed is:
