Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1 FIELD OF THE _ MENTION
This invention relates to soldering systems and methods and
more particularly to a system and method for the vapor-phase heating
o-F a product and separate application of solder to the heated
product.
BACKGROUND OF THE INVENTION
Soldering is widely employed for the fabrication of many
different products, especially products in the electronics field,
notably printed circuit boards. For the production fabrication Go
printed circuit boards and similar products, wave solder systems
have been widely employed. These systems include a reservoir of
molten solder which is pumped in a wave, with the circuit board
being transported in contact with the wave to cause wetting of the
intended areas of the board. the solder wave serves as a source of
heat for heating of the circuit board and also as the solder source
for application of solder to the board. The wave solder apparatus
is relatively complex and must be carefully designed and constructed
to provide a solder wave of the appropriate dimensions and
characteristics to provide the requisite heating and solder
application to the particular product being processed. The length
of the wave must be sufficient to provide sufficient time of contact
to heat the surface to be soldered. The wave design is critical in
: relation to the product and speed of the product through the wave.
There is a maximum speed beyond which a product cannot be conveyed
through a particular solder wave and still achieve sufficient
heating. For greater speeds the wave would have to be
; reconfigured, which would necessitate a complete system redesign.
The height of the solder wave is also a critical factor and can
be a limiting factor to the size of a product being processed. For
example, in a printed circuit board in which leaded components are
1 inserted, the lead lengths cannot be longer than the depth of the
solder or else a board cannot be accommodated in a particular wave
solder apparatus because of interference with the long component
leads. Thus, care must be exercised in the assembly of components
on a circuit board to assure that the lead lengths are less than the
depth of the solder wave for the particular solder apparatus to be
employed. Since the solder wave serves both as the source of solder
and source of heating, the dynamics of the system become complex in
designing a wave solder apparatus for particular purposes. Also,
these dynamics make it difficult to alter the characteristics of the
solder wave to accommodate different types of products.
Another type of production solder system is the drag solder
system in which a reservoir of solder is provided into which a
product is dipped and immersed either partially or completely to
apply solder to the product. Here again the molten solder serves
both as the source of heat for heating the product to a soldering
temperature and as the solder applicator.
The Amman et at U. S. Patent No. Rev 30,399 shows a wave flow
soldering apparatus in which the solder wave is provided at the
bottom of a vessel containing a heated, saturated vapor. The
product is convoyed through the vapor chamber and is heated by
immersion in the vapor phase and soldered by passage through the
solder wave. Solder is applied in an anaerobic atmosphere provided
by the vapor phase but there is little improvement in the control or
perforlnance of the soldering operation by location of the solder
wave apparatus in the chamber. The criticality and relative
complexity of the solder wave remains the same as described above,
and the presence of the solder wave within the heated vapor does not
alter the critical design considerations of the wave apparatus.
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1 An article entitled "A New Soldering Process," by W. R. George,
Brazing & Soldering, No. 5, Autumn 1983, shows a drag soldering
system in which the product is initially placed within a heated
inert vapor phase prior to immersion into the molten solder bath.
The Sarnacki et at U. S. Patent No. 3,825,16~ shows a soldering
system having a tank containing a pool of molten solder at the
bottom and covered by a liquid fluxing bath, with solder spray
apparatus within the fluxing bath. A printed circuit card is
inserted vertically into the fluxing bath for fluxing and
preheating, and solder is sprayed onto one or both surfaces of the
printed circuit card as the card is withdrawn from the tank.
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1 SUMMARY OF THE INVENTION
The present invention provides a system for the soldering of
circuit boards and other products in which the product is heated by
an independently controlled vapor phase system, and solder applied
by a separately controlled nozzle applicator system operative to
direct controlled and defined streams of solder onto the product. A
vessel is provided for containing a heated saturated inert vapor
into which the product is introduced prior to solder application and
by which the product is heated to soldering temperature. One or
more nozzles are provided within the vessel for directing one or
more streams of molten solder to the heated product, the impinging
solder being retained by the areas of the product surfaces to which
the solder will adhere. In the case of a circuit board, the solder
is adherent to the conductive circuit paths, the plated-through
holes which may be present in the circuit board, and to the leads or
connection pads of components assembled on or inserted through the
board.
Heating of the product is provided substantially by the heated
vapor phase atmosphere within the vessel, and the establishment and
control of this vapor atmosphere is separately provided by the vapor
phase apparatus. Solder application is provided by the applicator
nozzles which, with the associated solder pump and solder source,
independently provide the intended solder streams for the particular
product. Thus, the heating of the product and solder application to
the product are separately controlled operations, and these
operations are substantially independent of each other. The product
can be introduced and removed from the processing vessel in any
manner suitable for the particular application. Typically, for a
continuous production process, the product is carried on a conveyor
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in-to the processing vessel for heating and solder
application, and then carried by conveyor out of the
vessel.
According to a still further broad aspect of
the present invention, there is provided a vapor pro-
cussing system which comprises a vessel for containing
a processing vapor. Means is provided for heating
electronic liquid contained within the vessel to stab-
fish a zone of saturated vapor. Means is provided
for conveying work product through the saturated vapor
zone. Horizontally extending nozzle means is also
provided for directing a stream of molten solder against
a surface of work product as it is conveyed through
the saturated vapor zone. Means is also provided for
varying the position of the directing means and in-
eluding conduit means for supplying molten solder to
the nozzle means. The conduit means is connected at
one end of the nozzle means and pivotal supported
at the other end. The means for varying the position
also includes vertical link means connected at one
end to the one end of the conduit means and including
aperture means at the other end. It also further in-
eludes yoke means having means for cooperating with
the aperture means for raising or lowering the vertical
link means whereby -the vertical location of the nozzle
means can be changed.
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1 DESCRIPTION _ THE DRAWINGS
The invention will be more fully understood from the following
detailed description taken in conjunction with the accompanying
drawings, in which:
Fig. 1 is a diagrammatic elevation view of a soldering system
in accordance with the present invention
Fig. 2 is a diagrammatic elevation view of an alternative
embodiment of the system of Fig. 1 having a single nozzle disposed
below the product
Fig. 3 is a diagrammatic elevation view of a further
alternative embodiment of the system of Fig. 1 having a single
nozzle disposed above the product;
Fig. is a diagrammatic elevation view of the system in a
preferred implelnentation;
Fig. 5 is a partially cutaway top view of the system of Fig. I;
and
Fig. 6 is a partially cutaway pictorial view of a solder nozzle
assembly.
1 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
__ _ . _____
A soldering system in accordance with the invention is shown in
a preferred embodiment in Fig. 1, this embodiment being especially
suited to the soldering of electronic circuit boards. A closed
vessel 10 defines an interior vapor phase chamber in which a zone of
inert saturated vapor is provided at a predetermined elevated
temperature for heating of a product to be soldered. Heaters 12 are
disposed at the bottom of vessel 10 and are operative to heat a
vapor phase liquid 14, typically Fluorinert FC-70, to a temperature
sufficient to provide a heated saturated vapor of that liquid within
the chamber. Cooling coils 16 can be disposed around the vessel
walls at a position to define the upper extent of the vapor zone
within the chamber. Products such as circuit boards 27 are conveyed
into the vapor phase chamber by means of an entrance throat 18, and
out of the chamber by means of an exit throat 20, each throat
outwardly extending from opposite side walls of the vessel 10. A
conveyor 22 extends through the entrance throat 18, interior chamber
of vessel 10 and exit throat 20, and is operative to convey or
transport the circuit boards into and out of the vapor phase
20 chamber. The conveyor can be of any suitable form to accommodate
the particular product being processed. For circuit boards, the
conveyor can include frames for holding the board edges, leaving the
board surfaces exposed for soldering. A pair of nozzles 24 and 26
is disposed in the vapor phase chamber, each in a position to apply
25 to a stream of solder onto respective opposite surfaces of the
circuit boards which are conveyed past the nozzles along the product
travel path within the chamber.
A solder pump 28 is disposed within the vessel 10 in a sup 30
containing molten solder to provide solder to nozzles 24 and 26.
The sup 30 collects excess solder which falls or drains from the
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1 boards after solder application by the nozzles. The sup also
serves as a solder supply or source for the pump 28 and the nozzles.
A separate solder source may alternatively be provided. The solder
sup can alternatively be disposed external to the vessel.
The entrance and exit throats are preferably configured in
conjunction with the vessel to minimize the outward flow of vapor
from the vessel to the atmosphere. Such configuration can be as
shown in U. S. Patent 4,389,797 of the same assignee as this
invention. The present invention is not limited to use with such
entrance and exit throats, as many different forms of product
ingress and egress to and from the vessel can be provided to suit
particular product configurations and specific operational
requirements. It is preferable for continuous processing to provide
a straight-through or substantially straight-through system in which
the product can be conveyed continuously through the system for
soldering operations. The entrance and exit throats I and 20 can
be disposed in a substantially horizontal position or can be
inclined upward or downward to provide an intended conveyance path
and the requisite minimization of vapor loss from the throats to the
atmosphere.
The heating of a product entering the vessel chamber, and the
application of solder to the heated product, are separately
controllable and are each substantially independent of the control
of the other. The product entering the chamber is heated by the
I vapor phase atmosphere within the chamber. The establishment and
control of the heated vapor atmosphere is provided by the vapor
phase apparatus which includes the heaters 12 and vapor phase
liquid 14 and the associated heater control. The solder application
is provided by the applicator nozzles 24 and 26, and associated
source 30 and pump 28, which are constructed and adjusted to provide
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1 the intended solder streams for the product which has prior to
solder application been heated to an intended temperature by the
vapor phase apparatus of the system.
If only one side of the circuit boards 27 is to be processed,
the system can be implemented with only bottom nozzle 269 as shown
in Fig. 2, or with top nozzle 24, as shown in Fig. 3.
The system of Fig. 1 is shown in typical implementation in
Figs. 4 and 5. A pair of conveyor chains 31 and 32 are coupled to
frames 34 spaced along the chains and which are operative to retain
printed circuit boards for transport through vessel 10. The
frames 34 are each coupled at their forward end by a coupling 35 to
the driving chains 31 and 32, and include side members or skids 36
which slide along guide surfaces 38 within the vessel 10. The guide
surfaces within the vessel follow a downward path, illustrated by
reference 40, at the entrance portion of the vessel and then follow
a uniform upward path through the vessel which is substantially
colinear with the exit throat 20. A pair of idler wheels 42 and 44
is provided within the vessel for the respective chains 31 and 32 to
change the direction of chain motion, as illustrated. After
entrance of a frame and the circuit board carried thereby into the
vessel, the Frame and circuit board follow the path of the guide
surfaces 38 and assume an upward inclined orientation as shown in
Fig. 4 for linear upward travel through the processing chamber. The
circuit board, by this means, is conveyed in an intended orientation
for uniform travel past the solder nozzles so that an intended
relative position between the board surfaces and the confronting
nozzles can be maintained within the shortest convenient vessel
length in order to minimize the length of time that the circuit
board is subject to the high temperatures of the processing zone
within the vessel.
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A pair of hold-down plates 64 is disposed above
the conveyor to resiliently urge the side skids 36
of the conveyor frame into engagement with guide sun-
faces 38 and hold the frame and circuit board contained
5 by the frame down against the guide surfaces. The
circuit board is thus maintained in an accurate guided
position and orientation along its path past the solder
nozzles.
The solder nozzles 24 and 26 are provided on
10 respective sides of the board transported there between
astride the travel path, and each nozzle is adjustable
in the angular orientation of the nozzle orifice with
respect to the circuit board, and in the offset or
spacing of the nozzle from the confronting board sun-
15 faces. Typically, the nozzles are angularly adjustable over a range of 45 degrees to either side of an axis
normal to -the board surface, and are adjustable in
offset from the board surfaces in the range of I - 1
inch (0.64 2.54 cm). The lower nozzle 26 is further
20 illustrated in Fig. 6 and comprises an elongated goner-
ally cylindrical tubular member 50 having an elongated
linear orifice 52 along the length thereof and of length
sufficient to provide a solder stream across the entire
circuit board width. The member 50 has a lip 54 adjust-
25 able with respect to a lip 56 to provide an adjustable orifice. Typically, the orifice has a gap in the range
of 10 - 30 miss. The cylindrical member 50 is rotate
able about its axis to provide for angular adjustment
of the orifice 52 to the intended angle of incidence
30 of the solder stream applied to the confronting board
surface. A vertical link 58 is coupled to the member
50 for upward and downward adjustment of member 50 to
select the spacing between the nozzle and the confront-
in board surface. Vertical displacement of the Yen-
35 tidal link 58 is controlled by a yoke assembly 66 which
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includes a yoke 70 secured at one end to a horizontal
shaft 68. A horizontally extending pin 72 is secured
to the other end of the yoke 70 and cooperates with
an aperture in the form of a slot 74 which inclines
downwardly from the open end of the slot. The upper
nozzle 24 is similarly adjustable in offset from the
confronting board surface and angular orientation.
Molten solder is pumped to the nozzles via piping 60
which is coupled to a supply
1 manifold 62 which in turn is coupled to the molten solder source or
sup.
Each of the nozzles is adjustable to provide a selectable
angular orientation of the nozzle with respect to the confronting
board surface, and to select the gap or distance between the nozzle
and the confronting board surface. The angular adjustability of
each nozzle provides an angle of incidence for the impinging solder
stream which can be normal to the board surface or at an angle with
or against the travel direction of the board. The angular
orientation of each nozzle and the distance between the nozzle and
board surface is determined to provide the intended quantity of
solder and definition of the solder stream for the particular
product being processed. The solder streams are separately
controlled to provide the intended application of solder. Since the
product prior to solder application has been heated by the vapor
phase within the vessel to soldering temperature, the solder
application nozzles need be controlled only to provide the desired
solder application, and not to heat the product.
The system is useful in soldering a variety of circuit board
types. The system can be employed for so-called bare boards which
are printed circuit boards having circuit patterns on one or both
board surfaces without any components thereon, and which can include
through-holes interconnecting the circuit patterns. The system can
also be employed for circuit boards containing surface mounted
components on one or both surfaces thereof, leaded components having
leads which extend through the board, or a mixture of leaded and
surface mounted components. The apparatus of the illustrated
embodiment can be employed with either or both solder nozzles
operative for a particular processing run. In some cases, solder
need only be applied to one board surface, in which case the other
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1 solder nozzle can be deactivated by appropriate valving of the
solder supply to that nozzle.
The system can also be employed for solder stream application
by a nozzle to one board surface, with reflow soldering provided on
the opposite board surface. In some types of circuit boards, it is
preferable to attach components on a board surface by reflow solder
techniques in which, for example, a solder paste is applied to the
board, and the board thereafter is heated to cause the solder paste
to reflow and form a bond between the associated component and
conductive areas of the board surface. Reflow soldering can be
accomplished in known manner by the present system by introduction
of the circuit board into the heated saturated vapor within the
vessel. The opposite board surface can be soldered by the solder
stream from the associated nozzle. The present system is therefore
versatile in providing both solder stream and reflow solder
capability within a single apparatus, all within the environment of
the heated vapor phase.
The vapor phase atmosphere within vessel 10 is heated to a
temperature typically in the range of 415 - 450F. (213 - 232C.).
The solder source is maintained typically in the same range. The
solder within sup 30 is maintained in molten state by the heated
environment within the vessel. Alternatively, separate heaters can
be provided in or around the sup to maintain the solder at intended
temperature. The vapor phase atmosphere is therefore at a
temperature sufficient for heating the circuit boards to soldering
temperature so that, prior to solder stream application by the
solder nozzles, the product is already at the soldering temperature.
The solder stream of each nozzle is determined in relation to the
viscosity of the molten solder, the pressure provided by the pump 28
and the orifice dimensions of the nozzle to produce the intended
1 stream configuration for proper impingemerlt of solder upon the
board. The product is conveyed through the system at a speed
sufficient to provide heating of the board by the vapor phase
atmosphere within vessel 10 and proper application of solder to the
heated product. In typical implementation, the circuit boards are
conveyed through the vessel at a speed of 4 - 10 feet per minute
(1.20 - 3.05 meters per minute).
The invention is not to be limited by what has been
particularly shown and described except as indicated in the appended
claims.
