GB2199526A

GB2199526A - Soldering/desoldering apparatus

Info

Publication number: GB2199526A
Application number: GB08728409A
Authority: GB
Inventors: William J Siegel; Louis A Abbagnaro; Linus E Wallgren; Ararat Amirian
Original assignee: Pace Inc
Current assignee: Pace Inc
Priority date: 1986-12-11
Filing date: 1987-12-04
Publication date: 1988-07-13
Anticipated expiration: 2007-12-04
Also published as: GB2199526B; GB8728409D0; DE3742074A1; IT1223249B; FR2608351A1; IT8722933A0

Description

2199526 Portable apparatus utilizing molten solder for procedures such as

soldering and desoldering.

E1ELD OF THE INVENTION This invention relates to a method and apparatus utilizing pneumatic pressure for raising molten solder to a working position to effect soldering/desoldering of components mounted on a PCB or the like to thus facilitate the insertion or removal of components therefron. or to effect other operations.

BACKGROUND OF THE INVENTION

Various techniques are known for applying molten solder to a PCB havinc throuch-'.-!e mounted components - -o effect soldering and/or desoldering operations. Of the known devices, they generally fall into two Categories. The first consists of a solder bath where a container is provided for the inolten solder and the solder simply sits in the container, there being no movement of the solder. The leads of the components to be are -:izue= intc the bath to effect either soldering or deszlder-Jnc thereof. This technique is unsatisfactory in that the entire surface area of the solder is exposed to the air and tends to be oxidized thus forming contaminants for the above -I- 1 4 operations. Further, other contaminants may be introduced into the upper surface of the bath due to the soldering and/or desoldering operations. In a relatively short time the dross (as the above contaminants are sometimes collectively called) must be removed in order not to compromise the soldering/desoldering operations or other means must be used to accomodate this problem.

In another system, a fountain effect is provided whereby the solder is raised through a first path through an opening to form a fountain which contacts the area of the PCB to be processed, the solder then being returned to the main solder supply via a second path. Such a device is disclosed in 'U.S. Patent 4,162,034. Such devices also involve a large exposure of the solder to the ambient air thus introducing a large degree of oxidation which ultimately shortens the useful 1 ife of the solder supply. Hence, the solder supply must be relatively frequently replaced in order not to compromise the integrity of the soldering/desoldering process.

Other prior art directed to the use of molten solder for soldering and desoldering operations includes U.S. Patents 2,986,108; 3,990,621; 3,993, 235; 4,315,590; 4,412,641; 4,4237,605; and 4,523,708.

Another solderina/desoldering device is described in U.S. Patent 4,659, 002 assgned to the assignee of the present annlicat-Jon and incorporated by reference herein. The device of this patent is characterized in one aspect thereof in that the solder is raised to the upper surface of a hollow 1 applicator having an open top. The mechanism employed for raising the solder is a piston and cylinder type arrangement. Although this arrangement is useful in certain applications, it does have a drawback in other applications such as soldering or desoldering. That is, when soldering or desoldering, the PCB is placed above the applicator and means are employed to hold it in place. However, since the solder is raised to the uppermost level within the applicator and since it is sometimes difficult to control the pressure exerted by the piston and cylinder arrangement, there is at times a tendency for the solder to break through the holes and flow onto the upper surface of the board. Moreover, the piston tends to bind in this type of application.

In order to solve the foregoing problem, one aspect of the present invention is to employ pneumatic means for rai sing the solder to the uppermost level of the applicator. Accordingly, the pressure can be very accurately controlled to prevent solder breaking through the holes of the PCB. Other prior art devices have employed pneumatic means in connection with soldering/desoldering utilizing molter solder such as the above mentioned U.S. Patent 4,162,034. However, as stated above, the foregoing patent is directed to the formation of a fountain which flows against the area of the PCB to be processed. The disadvantages of this process in terms of contamination of the solder have been discussed above. This contamination problem is overcome in the above mentioned related application and in the present invention in that the surface area of the solder

1 normally exposed to the atmosphere is quite small compared to the total service area of the solder employed in the system. Further, the solder is raised to the top of the applicator only when needed for a soldering/desoldering operation or other special operation. It is immediately lowered after the operation and thus, for this further reason, contamination of the solder is kept to a minimum. The latter system is known as a dynamic balance system in that the solder is dynamically balanced at the uppermost level of the nozzle during soldering/desoldering. This is in contradistinction to the static solder bath or the free flowing fountain types of systems. The use of pneumatic pressure in a dynamic balance system overcomes not only the problems associates with U.S. Patent 4,162,034 but also those which are occasionally encountered in the system of U.S. Patent 4,659,002.

SUMMARY OF THE I?;VENTION

It is thus a primary object of the invention to provide in a dynamic balance syster., pneumatic means for effecting the dvnaimic balance.

It is a further object of this invention to provide a pulsating pneumatic source whereby the rise of solder to the level of '--e app'-."Lcator may be accurately controlled.

It is a further object of this invention to provide a pulsating pneumatic source whereby the solder may be automati ally returned to the same level in the applicator each time a n,,lten solder operation is performed.

-4 1 1 1 i 1 It is a further object of the present invention to provide a pulsating pneumatic means in a dynamic ba lance'system whereby small ripples or waves are formed at the upper surface of the solder in the nozzle to facilitate a soldering/desoldering operation due to agitation introduced by the above mentioned waves or ripples.

It is a further object of this invention to provide an improved applicator consisting of a removable nozzle having an open top.

It is a further object of this invention to provide a plurality of such removable nozzles for use in a desolder-solder system employing molten solder whereby components or connectors of different sizes and configurations mounted on a.PCB may be readily accommodated.

It is a further object of this invention to provide'an improved solder reservoir for fountain tyPe system which is manufactured and maintained.

It is a further object apparatus for providing pulsed use in.a dynamic balance or easily and economically of this invention to provide pneumatic means for a soldering/desoldering system employing molten solder.

It is a further object of this invention to provide improved electrical circuitry for controlling the above mentioned pulsed pneumatic means.

It is a further object of this invention to provide improved auxiliary heating sources for use with this invention, such sources being useful when the job to be performed is larger in size than the capacity of the deployed desoldering/soldering system.

According to the present invention there is provided apparatus for performing an opera,ion on a workpiece with molten solder, said apparatus comprising a substantially enclosed molten solder container, a contained space being disposed within the container above the molten solder; a tube for conveying the molten solder in the container to the workpiece where the ratio of the transverse cross-sectional area of the container to the transverse cross-sectional area of the tui>e is no more than about 10:1; and a source connected to said contained space for introducing a pressurized gas into the space to raise the solder through said tube to a predetermined level adjacent said workpiece and maintaining said solder at said predetermined level to thus effect said operation with the molten solder.

BRIEF DESCRIPTION OF THE DRAWING

Figure 1 is a cross-sectional view of an illustrative, job oriented, multilead soldering/desoldering apparatus for use with the present invention.

Figure 2 is a schematic view of an illustrative pressurized air source for use with the system of Figure 1.

Figure 3 is a timing diagram illustrating various cycles of operation of the apparatus of Figure 1 under the control of the pressurized air source of Fi79ure 2.

Figure 4 is a block diagram of an illustrative pressurized air controller for use in the pressurized air source of Figure 2.

Figure 5 is a cross-sectional view of an illustrative auxiliary heating source for use with the system of Figure 1, for example.

Figure 6 is a cross-sectional view of another illustrative, auxiliary heating source for use with the system of Figure 1, for example.

Figure 7 is a cross-sectional view of a PCB positioned above but not in contact with the nozzle of the present invention.

Figure a is a cross-sectional view of an improved, portable soldering/desoldering device in accordance with a further modification of the invention.

Figure 9 is a partial cross-sectional view taken along the line 9-9 of Figure S.

Figure 10 is a partial cross-sectional view of a modification of the embodiment of Figure S.

Figures IIA through 14A are illustrative cross-sectional views of various configurations which may be employed for the nozzle 214 of the device of Figure 5 or the upper portion of the tube 206 of Figure 7.

Figures IIB and 11C are possible plan views corresponding to the crosssectional view of Figure 11A; Figures 12B through 12D are possible plan views corresponding to the cross-sectional view of Figure 12A, Figures 13B and 13C are possible plan views corresponding to the cross-sectional view of Figure 13A; and Figures 14B and 14C are possible plan views corresponding to the cross-sectional view of Figure 14A.

Figure 15A is a,plan view of a nozzle adapted for a transistor or the like.

Figure 15B is a cross-sectional view which illustrates the meniscus molten solder forms when the solder is raised to the uppermost level of nozzle 214 of Figure 8 or tube 206 of Figure 10.

Figures 16 and 17 illustrate various working or positional relationships of a printed circuit board or the like with respect to the meniscus of Figure 12.

Figures 18 and 19 are directed to modifications of the invention where the molten solder is directed over a further tube inclined with respect to the vertical through a capillary tube disposed at the distal end thereof for dispensing molten solder wherein Figure 18 the further tube is non-flexible while in Figure 19 it is flexible.

Figure 20 is a partial cross-sectional view where a capillary tube is disposed on a vertically oriented tube.

Figure 21 is a perspective view of a simplified locating system for use with the invention.

DETAILED DESCRIPTION OF PRZFERR.ED EMBODIMENTS OF THE INVENTION

Reference should be made to the drawing where like reference numerals refer to like elements and components of the invention.

Referring to Figure I there is illustrated a ruiti-lead desoldering/soldering system in accordance with present invention generally including a nozzle 10, a solder reservoir 12, and a pressurized air source 15. As will be described in more detail hereinafter, the system of the present invention is job oriented -- that is, solder is applied to a work 14 from reservoir 12 to nozzle 10 only during the time the work rea'aires the solder for a desoldering or soldering operation. As can be seen in Figure 1, the work is positioned on the nozzle 10 where the work may comprise a substrate such as a r.

1 printed circuit board (PCB) having mounted thereon a number of components and/or connectors where the components and/or conn ectors typically are mounted with.through the board leads or pins. As can be seen in Fig-ure 1, component 16 has leads 18 which extend through holes (not shown) in the board 20, the leads being soldered at the surface 22 of the board to pads or connectors-printed on surface 22 in a known manner. Although normally intended for use with components having through the board leads or pins, the invention may also be used with surface mounted devices (SMD's) where such devices would be mounted on the surface 24 of the board as indicated by the dotted line SMD 26 as will be further discussed below..

As will be described. further below, the nozzle 10 may have a number of different configurations, either rectangular, circular, square, or other special configurations depending upon either the configuration of the device to be removed or installed or some special procedure to be performed. Typically, the nozzle has an open top and the walls thereof are made of a material such as stainless steel and very thin in order to minimize heat co.nductivity and heat capacity. Disposed in the bottom center portion of the nozzle is an opening 28. A tubular, tapered plug 30 is attached to the bottom of the nozzle, the opening 32 extending through the plug having a diameter preferably substantially the same as or exactly equal to the diameter of the opening 28 in the bottom of nozzle 10. The plug 30 is typically also made of stainless steel.

The plug 30 is removably insertable into an intermediate, tubular, tapered plug 34. This Plug also may be made of a low heat conductivity, low therma mass material such as stainless steel. Plug 34 is removably insertable into a tubular member 36 comprising a portion of a cover generally indicated at 39. Notches 38 are provided at the sides of intermediate plug 34 to facilitate the removal of plug 34 from tubular portion 36. Similar notches 39 are provided for plug 30. The inner opening of tubular portion 36 is inwardly tapered to receive the tapered portion of intermediate plug 34. Hence, it can be seen due to the outer tapers of plugs 30 and 34 mating with the inner tapers of plugs 34 and tubular portion 36, respectively, seals are formed between these respective members and thus the passageway 37 extending from the bottom 38 of tubular portion 36 to the lower opening 28 in nozzle 10 is sealed to solder flw. In some instances, the nozzle 30 can be so sized as to fit directly into tubular por-tion 36; however, use of intermediate plug 34 is preferred to provide separation from the heated reservoir 12 and the work 14, and to simplify the design and manufacture of nozzle 10 and its associated plug 30.

The reservoir 12 includes basically two members comprising a molten solder container 40 and a cover 39 where both of these elements are typically made of cast iron or a material Liar thermal characteristics and capability of not having sin-L contaminating the solder. Typically, the general shape of container 40 is cylindrical although it may be rectangular or any other configuration. Heating elements 42 and 44 may be disposed in the lower portion of the container to heat the solder to A temperature of about 300 - 6000F. A temperature sensor generally indicated at 43 includes a probe 45, a connector 47, and a temperature sensor circuit 51. The temperature sensor may be employed on an open-loop basis to permit manual maintenance of the solder at a desired temperature or on a closed-loop basis to effect automatic temperature maintenance in a known manner.

The upper portion of container 40 is provided with a flange 46. The cover 39 for the reservoir includes-a downwardly extending wall 49 which extends between the upper portion 48 of tubular member 36 to a flange portion 50 of the cover. The upper, interior surface of wall 49 is provided with a tapered surface 52 which mates with a tapered surface 54 provided on the interior surface of container 40 adjacent the flanged portion 46 thereof. Accordingly, the cover 41 may be fitted onto the container 42 and a hermetic seal will be provided between the tapered portions 52 and 54 due to the force fit therebetween. Other known means may also be employed to obtain a hermetic seal between the cover and container.

The force fit between tapered portions 52 and 54 may be effected by a plurality of (for example, four) bolts disposed around the periphery of cover 39 and extending through flanges 46 and 50, one of these bolts being indicated at 61. The bolts 61 also hold --,n place a respective plurality of U-shaped brackets 63, which suspend reservoir 12 above base 70, the inner surfaces of the brackets being covered with a thermal insulating material 65 to isolate them from the heated reservoir. Thermal insulating material (not shown) may also be packed about the reservoir for further thermal isolation of the reser-voir.

The initial solder level in container 12 is typically at level 56. As can be further seen, cover 39 covers most of the solder in the container and, in particular, that beneath wall 49 is almost completely isolated from the atmosphere due to the hermetic seal established between tapered portions 52 and 54. Due to this isolation, it has been found that build up of dross over a long period of time is kept to a minimum. Moreover, since dross such as oxides and the like tend to rise to the upper surface of the molten container, this dross, if any, will tend to be at the surface 56. Since it is located at surface 56, it cannot contaminate soldering or desoldering operations performed by the system 10.

The lower portion 48 of wall 49 is provided with a groove 58 on the exterior surface thereof, the purpose of this groove being to capture any solder which accidentally or intentionally overflows nozzle 10. In most soldering/desoldering operations, it is preferable that the solder be brought to the uppermost level of nozzle 10 and maintained there, this level being indicatei at 60 in Figure 1. Normally, this level can be quickly established without overflow over the sides 62 of nozzle 10 into the cup 64 defined by the upwardly extending wall 49. However, there are instances when it may be desirable to remove a minor anount of dross which may accumulate at the upper surface of the solder when it is in its raised position at the uppermost level 71 of container 10. In these instances, it is possible under the control of pressurized air source 15 to overflow the solder including the dross therein into cup 6 4 where it accumulates in circular groove 58 disposed at the bottom of cup 64. The purpose of groove 58 isto permit the removal of removable plug 34 without allowing the contaminated solder in groove 58 to return to the solder in container 40 via the passageway through tapered, tubular member 36. Hence, the purity of the contained solder can be maintained at a high level for a long period of time. That is, even though some of the solder is removed from the system by overflowing it to remove dross, as described above, the amount of remaining solder is just as effective as the amount of original solder for soldering, desoldering and other operations. This remaining solder can also be quickly brought to the uppermost level of nozzle 10 under the control of source 15, as-will be described below.

Tubular portion 36 includes a flat portion 66 disposed at the upper surface thereof inside groove 58, the flat portion contacting removable insert 34. When initially filling reservoir 12 with molten solder or when refilling the reservoir# flat portion 66 may act as a fill line. That is, with the nozzle 10 and plug 34 removed, an operator can easily visualize when the solder has risen within tubular portion 36 to a level correspondIng to flat portion 66. Thus, the level of the solder within the portions 68 covered by wall 49 can readily be established with a high degree of accuracy at the level shown in Fig-ure 1. This level will permit long lasting, effectively 1 contaminate free operation of the system before replacement of the molten solder is necessary.

As stated above, only the relatively small surface of the solder extending into passageway 37 is exposed to the atmosphere and thus contamination of the solder by oxidants and the like is held to a minimum. This is in contradistinction to the typical solder bath where the entirety of the upper surface of the bath is exposed to the atmosphere to continually contaminate the entire upper surface thereof and thus introduce significant problems relating to contamination of the soldering and/or desoldering procedures. Moreover, in the system of Figure 1, any contaminants which do form at the upper surface of the solder extending into passageway 37 tend, with operation of the system (as the solder is raised to the uppermost level of the nozzle 10 for a job), to be deposited on the side wall of passageway 37 such that uncontaminated solder is presented to the job at the nozzle, and with further operation of the system (the solder is returned to level 56), the dross in passageway 37 passes doi,,nwardly and around the bottom end 38 of the tubular portion 36 into the solder located in the cavity 68 under wall 49. There the contaminants rise through the solder in cavities 68 to the upper surface of the solder in these cavities where they are no longer able to reach the working surface at the upper level of nozzle 10 and thus they are rendered ineffective as contaminants of the solder/desolder operation of the system.

As stated above, the configuration of nozzle 10 may assume various shapes depnding upon the application. For r 1 G i example, the configuration of a nozzle may conform to the configuration of a component to be removed or inserted,or it may be generally configured to permit insertion or removal of several components at the same time. Furthermore, the nozzle may have more than one opening at the top to respectively accomodate more than one component on the board. Moreover, compartments may be provided within the nozzle.. to restrict application of the solder in each compartment to a particular area of the job. In typical usage, it provides safe, fast removal and replacement for S.I.P. and D.I.P. packages, connectors-and pin.grid array (P.G.A.) packages. Further, the system may be used with PCB's having plated through holes, double sided multilayer or flexible. In particular, with respect to single and dual in line packages, the nozzle may be shaped to all known configurations. For pin grid arrays the nozzle config- uration typically can handle a maximum size of at least 2 1/2 by 2 1/2 inches while for connectors it can handle a maximum size of at least 1/2 inch by 18 inches. A standard size nozzle may typically comprise a hollow, rectangular, parallelopiped with an open top which can solder/desolder D. I.P. packages having up to 40 leads, the nozzle being 3 inches long in the horizontal direction of Figure 1 by.75 inches wide in the direction perpendicular to the plane of Fig-ure 1 and.7 inches deep in the vertical direction of Figure 1. Another standard nozzle could have a square cross section for pin grid arrays, the nozzle being 2 1/2 inches by 2 1/2 inches by.7 inches deep. Other nozzle configurations which would have wide -Is- applicability would be tlose with the following rectangular cross sections - namely, (a) six inches long by.75 inches wide by.7 inches deep, (b) nine inches long by.75 inches wide by.7 inches deep, (c) twelve inches long by.75 inches wide by.7 inches deep, and (d) eighteen inches long by.75 inches wide by.7 inches deep. In some of the latter configurations, an auxiliary heater mechanism may be required due to the size thereof. Such mechanisms are described hereinafter with respect to Fig-ures 5 and 6.

Reference should now be made to Figure 2 which shows in further detail pressurized air source 15 of Fig-ure 1. In particular, pressurized air source 15 includes an air pump 72 connected to the atmosphere or an inert gas container (not shown) via a filter 74. Pump 72 is connected to solder reservoir 12 via a needle valve 76 and a three way solenoid valve 78. In a first position, solenoid valve 78 connects pump 72 to solder reservoir 12. In this position, as can be seen in Figure 1, the pressurized air delivered from pump 72 enters the confined space between cover 39 and the upper surface 56 of the solder and exerts a downward force on surface 56. Accordingly, the solder in passageway 37 rises, and as will be described in more detail hereinafter, continues to rise until it is typically at the uppermost level of nozzle 10. At this point the head of solder extending through passageway 37 into nozzle 10 is such as to correspond to the differential between the pressure being exerted on the surface 56 of the solder and atmospheric pressure. In a second position of solenoid valve 78, the 4 reservoir 12 is vented to the atmosphere through a flow control valve So. In this position of solenoid valve 78, the solder in nozzle 10 is allowed to return to its level shown in Figure 1. This typically occurs after a soldering or desoldering operation. The purpose of flow control valve 80 is to control the release of air to the atmosphere so that the solder in nozzle 10 returns to the level of Figure I at a relatively slow rate. Thus, solder joints formed in the plated through holes of board 20 maintain their integrity. If the solder were allowed to flow too quickly away from the joints formed within the holes, some of the solder would be drawn from the holes thus possibly severely compromising the integrity of the soldered joints. Moreover, if the solder is allowed to flow away too quickly, there is a tendency for icicles of solder to-form on the bottom of the board.

When solenoid valve 78 is in its second position, pump 72 is disconnected from the reservoir. Pump 72 is typically of the type where a predetermined amount of time (typically about 0.5 seconds) is required before the pump reaches its rated pumping speed. During this time, solenoid valve 78 will be in.its second position and the pump will be vented to the atmosphere via a normally closed, two-way solenoid valve 82. As will be further described below, solenoid valve 82 may be pulsed on and off to raise the solder in nozzle 10 to typically the uppermost level of the nozzle and to maintain the solder at this level. Such a pulsed, solenoid valve is described in an article entitled "Simple Pneumatic Servo Valve is Pulse Width Modulated" 1 Design News, February 17th, 1986, pages 164 through 166, a copy of the enclosed article being submitted herewith. The foregoing article is incorporated herein by reference. Needle valve 76 is typically preadjusted and provides coarse reg7ulation for the rise of solder from its position shown in Figure 1 to its final level within nozzle 10.

Pump 72 and solenoid valves 78 and 82 are under the control of a pressurized air controller 84, which will be described in further detail in Figure 4.

The operation of the pressurized air source 15 of Figure 2 will now be described referring to Figure 3, which illustrates the timing for various cycles of operation which typically occur for either a soldering or desoldering operation of the system of Fig-ure 1. Referring to the first cycle, which corresponds to the start up of pump 72, it can be seen the electrical outputs from controller 84 are such that the pump is on, solenoid valve 82 is ON (or open) while solenoid valve 2 is OFF (that is, in its second position). Thus, until the pump reaches its rated speed, air is exhausted through solenoid valve 82. As stated above, this typically occurs in about 0.5 second.

During the next cycle of operation, the electrical outputs from pressurized air controller 84 are changed such that solenoid valve 82 is switched OFF (that is, it is closed) while solenoid valve 78 is switched ON (that is, switched to its first position). Pump 72 remains on and thus pressurized air is.applied directly to reservoir 12 through needle valve 76 and valve 78 to raise the solder through passageway 37 into nozzle -IsW at a relatively high rate of speed. This high rate of speed is desirable in many instances in that the solder tends to lose.its heat as it is raised from the reservoir. Hence, if the rise occurs too slowly, the temperature of-the solder may drop to a point where the soldering and/or desoldering operation is compromised. Thus, in accordance with one aspect of the invention, the solder is initially raised at a high rate of speeduntil the solder reaches a predetermined percentage of its f inal, intended level. This percentage may vary depending upon the application; however, the percentage is typically at least 95 percent and preferably about 99 percent. As indicated in Figure 2, the fast rise time may be adjusted any where from 0 to 9.9.seconds. Of course, if a longer rise time is desired, such a rise time is also within the scope of the present invention. The fast rise time is typically a function of the size of nozzle 10. Hence, a fast rise time of about 4 to 5 seconds is desirable with a nozzle 6 to 8 inches long, 3/4 inches wide, and.7 inches deep.

After the fast rise time has elapsed, the outputs-from pressurized air controller 84 are again changed such that, as indicated in Figure 3, solenoid valve 82 has applied thereto a pulse train where the ON time of the pulse typically is constant at 50 milliseconds while the OFF time may be adjusted between about 0 and 99.9 milliseconds. Of course, these times are illustrative and may be varied within the scope of the invention. The output signals applied to solenoid valve 78 and pump 72 remain unchanged during this cycle. The length of this cycle may vary from 0 to 99.9 seconds where again these values are preferred but not intended to be limitative. At the beginning of the cycle switch 82 is turned OFF for a preset period of time within the 0 to 99.9 millisecond range mentioned above. Since valve 82 is closed and valve 78 is in its first position, pressurized air is supplied to reservoir 12 for the preset time interval which may be 75 milliseconds, for example.

After the 75 milliseconds have elapsed, the valve 82 has a 50 millisecond pulse applied thereto to open the valve and thus exhaust the air from pump 72 to the atmosphere although -some air is also applied to reservoir 12 since valve 78 remains in its first position during this time. However, most of the air passes through by valve 82 and thus the pressurized air from pump 72 is effectively removed from reservoir 12 for the 50 millisecond duration of the ON pulse.

In the foregoing manner, normally closed valve 82 is pulsed ON and OFF to open and close it and thus apply an effective pressure to the solder in the reservoir, the effective pressure being a direct function of the ratio of the OFF time to the ON tine of solenoid valve 82. The longer the OFF time, the greater the effective pressure and thus the higher the level the solder is raised to and maintained at in nozzle 10. The ratio of OFF tine to ON time of solenoid valve 82 is a function of the nozzle size as is the fast rise tine discussed above. As will be described below, this ratio can be calibrated to correspond to different nozzle sizes and thus the operator can immediately select the desired ratio depending upon the nozzle size employed.

I- k From the foregoing, it can be seen that the pulsing of solenoid valve 82 effects a slower, controlled rise of the solder in nozzle 10 to its final, intended level. Thus, as stated above, the solder is quickly brought up to about 99 percent, for example, of its intended final level during the fast rise cycle. Of course, the solder cannot be brought up to its final intended level by the constant application of pressure as is the case during the fast rise cycle since the solder will invariably over shoot the final level due to the momentum thereof. This is a particularly significant concern when the final intended level corresponds to the uppermost level of nozzle 10.. Any over shoot will result in overflow of the solder from the nozzle into cup 64. This is undesirable in that it is wasteful of the solder. Hence, by pulsing the pressure, it can be brought to a level even at the uppermost level of the nozzle without overflow of the solder.

Moreover, another advantage of pulsing the solder is that ripples or waves are created at the upper surface of the solder and this results in desired agitation of the joints being soldered or desoldered to thus enhance the-soldering/desoldering operation." A further advantage of applying pulses of air to the solder as opposed to a constant application of pressurized air is that the air is heated by the solder and thus expands. This expansion will change the level of the solder in the nozzle. Since the solder level in the nozzle should be maintained as accurately as possible, application of pulses of the pressurized air more accurately achieves this goal.

As shown in Figure 3, the length of the desolder/solder operation may typically vary from 0 to 99.9 seconds. This time is about 30 seconds for many procedures. Only about two cycles of the ON and OFF pulse train applied to solenoid valve 82 are shown in Figure 3. This is done for purposes of illustration. Of course, in practice, a large number of these cycles will occur during the desolder/solder operating cycle. The length of the cycle is mainly determined by the procedure to be performed and is under operator control as will be described with respect to Fig-ure 4.

At the end of the desolder/solder operating cycle, the output of pressurized air controller 84 again changes. Thus, as can be seen in Figure 3, pump 72 is turned OFF as are solenoid valves 80 and 82. Thus, the solder in the system of Figure 1 is allowed to return to its level shown in Figure 1. As stated above, the rate of return is controlled by flow control valve 82 to ensure the integrity of soldered joints.

Referring to Figure 4, there is shown an illustrative block diagram of pressurized air controller 84 of Figure 2. The controller includes a start switch 86 which initiates the various cycles of operation illustrated in Figure 3. The start button connects a voltage source V+ to a control circuit 88. The control circuit comprises a flip-flop. Thus, in particular, the start switch 86, when actuated, connects the V + voltage to the SET input of the flip-flop to cause the SET output thereof to go high. The SET output is applied as an ENABLE signal to a moll-or drive 90, which in turn controls a pump motor 92 which a Gr 1 drives pump 72 of Figure 2. The SET Output is also applied over line 94 to one input of a solenoid control circuit 96, the control circuit comprising a three-input AND gate. The output of the AND gate is applied to the base of an NPN transistor 98, the emitter of which is connected to ground and the collector of which is connected to the V+ voltage source via solenoid 82 of Figure 2. The SET output of the flip-flop is also connected to a delay circuit 100, the length of the delay corresponding to the length of the pump start cycle of Figure-3. Thus, this delay is approximately 0.5 second. In general, the delay should be sufficient to allow pump 72 to reach its rated pumping speed. The output of delay 100 is applied as an ENABLE signal to a timer 102 and to a timer 104. The output of delay 100 is also applied to a solenoid control circuit 106, the latter circuit being a flip-flop where the output from delay 100 is applied to the SET input of the flip-flop. The SET output of the flip- flop is applied to the base of a transistor 108, the emitter of which is connected to ground and the collector of which is connected to the V + voltage source through three-way solenoid valve 78 of Figure 2. A master clock 110,which typically r-uns at abou t 1 MHz, is applied to timers 102 and 104 and a further timer 110. Timers 102, 104, and 110 are co=ercially available from Intersil Inc. as Part Number ICM 7250. Respectively connected to the above timers are thumbnail switches 112 through 116, these switches being commercially available from the Cherry Switch Company as Part Number T65-02. Connected to the output of timer 104 is a delay circuit, the leng-th of the delay corresponding to the fixed length of the ON pulses (typically 50 milliseconds) applied to solenoid 78 and illustrated at 79 in Figure 3. This delay circuit may include means for varying the leng-th of the ON pulse where the amount of delay would be adjustable under operator control by means not shown. The output of delay 118 is connected to a reset input of timer 104.

The output of timer 102 is connected to one of the inputs of the threeinput AND gate comprising control circuit 96. The output of timer 102 is also connected over line 120 to the ENABLE input of timer 110.

The output of timer 104 is connected to the third input of the threeinput AND gate comprising control circuit 96. The output of timer 110 is connected to the RESET input of the flip-flop comprising control circuit 106. Also connected to the output of timer 110 is a reset line 124 which is connected to the RESET input of the flip-flop comprising control circuit 88. Application of the reset voltage to control circuit 88 resets all circuits comprising pressurized air controller 84. A stop switch indicated at 126 is connected between line 124 and the V+ voltage source and provides an emergency capability of shutting down the system of Figure 1 whenever this switch is actuated.

In operation, switch 86 is closed to SET control circuit 88 and thus apply an ENABLE signal to motor drive 90. The drive circuit thus actuates motor 92 to drive pump 72. The closure of switch 86 initiates the pump start cycle of Figure 3. The SET 1 output of control circuit 88 is also applied as a high level signal to the three-input AND gate comprising solenoid control circuit 96. Prior to enablement thereof, timers 102 and 104 have their respective outputs at the high level. Thus, all three inputs of the AND gate 96 are at the high level when the SET signal from control circuit 88 is applied over line 94 to the gate. Accordingly, the base of transistor 98 is raised to close the circuit including solenoid 82. Hence, the solenoid is turned ON (or opened), as indicated in the pump start cycle of Figure 3. Solenoid valve 78 will be OFF (that is, in its second position) at this time and since no action is taken during the pump start cycle to switch this valve, it remains OFF to thus permit the pump 72 to reach its rated pump speed during the pump start cycle of Figure 3.

1 As Stated above,.the pumps start cycle is timd by delay 100, the length of this delay being about 0.5 seconds. At the end of this time, an ENABLE signal is applied to timers 102 and 104 and the flip-flop comprising Solenoid control circuit 1,06 is SET. The setting of control circuit 106 closes the circuit through solenoid valve 78 to turn it ON and thus place it in its first position whereby it connects pump 72 to solder reservoir 12. This is shown in Figure 3 for the fast rise cycle.

As stated above, valve 82 is open during the punp start cvcle and is returned to its normally closed position at the beginning of the fast risecycle. This is effected by applying the ENABLE output from delay 100 to timer 102. The normally high output of timer 102 is thus switched to a low output to 1 1 thus de-activate the AND gate of control circuit 96 and switch the output thereof to a low level which turns off the transistor 98 and, accordingly, turns off solenoid 82 to return it to its normally closed position, as indicated in Figure 3. The duration of the fast rise cycle is determined by the setting placed in thumbnail switch 112 by the operator. In the embodiment of Figure 4 a fast rise time of 3.2 seconds is chosen. It should be noted that although the thumbnail switches are illustrated as giving three place accuracy, two place accuracy nay be appropriate in many applications. Of coursp, the number of places of accuracy can be varied depending upon the application. The output of the thumbnail switch 112 is an analog signal which is applied to timer 102, the magnitude of the analog signal corresponding to the setting of the switch and determining the number of clock pulses from source 110 which will be counted before the output of timer 102 is switched back to its normally high level. As stated above, the output of timer 102 is switched from its normally high level to a low level upon application of the ENABLE signal to the timer. The enable signal also effects counting of the clock pulses until the number thereof counted corresponds to the number set in thumbnail switch 112. At this time, the output of timer 102 will be switched back to its high level to again enable the AND gate of circuit 96. In particular, at this time, the fast rise cycle will be completed and the solder in Figure 1 will have been raised to a level which is about 99 percent, for example, of its final intended level at the uppermost level of nozzle 10.

1 1 In order to raise the solder to Its final level in a controlled manner, the output of timer 104 is now utilized. Timer 104 is enabled at the same time timer 102 is enabled. Thus, its normally high output is immediately switched to a low output and then a time interval corresponding to the time set in thumbnail switch 114 is timed in a manner similar to that described above for timer 102. However, the time set in thumbnail switch 114 is much shorter than that set in switch 112. In part-icular, in Figure 4, a time of 75 milliseconds is set into thumbnail switch 114. This time corresponds to the OFF time 81 shown in the desolder/solder cycle of Figure 3. Thus, when a number of pulses from clock source 110 are counted corresponding to the 75 millisecond time interval, the output of timer 104 will switch back to its high level as indicated at 83 in Figure 3. The positive transition 83 is also applied to a delay circuit or line 118, the delay of which is typically fixed at a predetermined value such as 50 milliseconds. Once this period of time bas elapsed, a RESET signal is applied to timer 104 from the output of delay 118 whereby the output of the is again switched to its low level and tiie timing function described above is again repeated to generate an OFF tine interval corresponding to the 75 millisecond value set in thumbnail switch 114. The foregoing generation of 75 millisecond OFF tine intervals and 50 millisecond ON time intervals is continued as long as the ENABLE signal is applied to timer 104.

At this time it should be appreciated that the foregoing pulse train is not applied to solenoid valve 82 during the fast rise time cycle. That is, as described above, during the fast rise time cycle, the output of timer 102 is low and thus none of the pulses generated by timer 104 are passed by the AND gate of circuit 96. However, at the end of the fast rise cycle, the. output of timer 102 returns to its high level which thus permits the AKD gate 96 to pass the pulses generated by timer 104. Two of the pulses thus passed by the AND gate are illustrated in the desolder/solder cycle of Figure 3. As stated above, eac h time a positive pulse is passed by the AND gate, solenoid valve 82 is opened to thus effectively prevent the application of pressure to solder reser-voir 12. Thus, during the 75 millisecond low level intervals of the output from timer 104, solenoid valve 82 is not actuated and is thus closed thereby permitting direct flow of air from pump 72 through solenoid valve 78 to the solder reservoir. The height the solder will rise in nozzle 10 is a direct function of the number placed in thumbnail switch 114. The larger this number, the higher the solder will rise. Hence, the height the solder does rise in nozzle 10 can be accurately set by appropriately controlling thumbnail switch 114.

As described above, it is typical to raise the solder in nozzle 10 to its uppermost level to thus facilitate good contact between the printed circuit board disposed on or above the nozzle. As discussed above, there are times when dross may accumulate at the upper surface of the nozzle and this can be removed by slightly overflowing the dross containing solder over the edges of the nozzle into cup 64. For example, if the setting 75 of Figure 4 corresponds to the solder rising to the uppermost level of the nozzle for the amount of solder employed in the system of Figure 1, drosscontaining solder may be overflowed from the nozzle by changing the setting of switch 114 to 77, for example. The thumbnail switch can then be left at 77 and the solder will again arise to the uppermost level of nozzle 10 preparatory to the next operation. That is, by overflowing some of the solder, the amount of solder in the system of Figure 1 is reduced since the overflowed solder is not returned to the system solder. Hence, a slightly greater pressure is now needed to raise the solder to the uppermost level of nozzle 10. The new setting of 77 in thumbnail switch 114 will accomplish this. Thus, once'the setting of switch 114 is such that the solder will reach the uppermost level of nozzle 10, the solder can be repeatedly raised to this level with a high degree of accuracy.

As indicated in Figure 3, the solder/desolder time is held for a predetermined period of time which may vary from 0 to 99.9 seconds, the length of this time primarily depending upon the job to be performed. In the embodiment of Figure 4, this time is chosen as 35.5 seconds. Thumbnail switch 116 applies an analog value corresponding to this time to timer 110. Timer 110 functions in the same way as described above with respect to timer 102 to time a predetermined interval by counting the clock pulses from clock source 110 for a length of time corresponding to the magnitude of the analog output from thumbnail switch 116. As-can be seen from Figure 3, the desolder/solder cycle commences immediately after the fast rise cycle. Hence, since timer 102 controls the duration of the fast rise cycle, the output thereof is utilized to apply an ENABLE signal over line 120 where the positive going transition which occurs at the output of timer 102 at the end of the fast rise cycle will ena.ble timer 110 to switch its normally high output to the low level thereof. This low level will be maintained for the length of time set in thumbnail switch 116 in the manner described above for the othei timers. The output of the timer will then switch high and be applied as a reset for the flip-flop comprising control circuit 106. This will end the desolder/solder cycle and commence the solder drop cycle of Fig-ure 3.

In particular, the resetting of flip-flop 106 returns solenoid valve 78 to its second position where it exlausts the solder reservoir to the atmosphere through flow control valve 80. At the same time, the transition to the high level at the output of timer 110 is applied to the reset input of the flip-flop comprising control circuit 88 over line 124. When the flip-flop is reset, the ENABLE signal applied over line 94 to the AND gate comprising circuit 96 is changed from its high level to its low level thus turning off (and thus closing) solenoid valve 82, as indicated in the solder drop cycle of Figure 3. Moreover, the enable SIGNAL is removed from motor drive 90 thusturning off pump 72, as also indicated in the solder drop cycle of Figure 3. Hence, a complete cycle for soldering or desoldering has now been described under the control of pressurized air controller 84. of course, as stated above, operations other than soldering or desoldering can also be implemented.

In case there is a need to stop the operation for an emergency or any other reason, stop button 126 may be closed to connect the V+ source to the reset terminals of the flip-flops comprising control circuits 88 and 106 and the solder drop cycle will immediately commence.

certain variations of the system as described above are possible such as implementation'of the function of pressurized air controller 84 by a software controlled microprocessor, the software being responsive to the settings of the thumbnail switches.112 through 116 or other appropriate input devices to control solenoid valves 78 and 82 and pump 72 in accordance with the timing diagram of Figure 3. Moreover,' for certain functions, a mechanical pump such as pump 72 need not be utilized and, in fact, a hand pump can be connected to inlet 83 of reservoir 12. Moreover, the circuitry of Figure 4 has been described in connection with automatic operation of the system; however, manual operation of the various cycles of the system can also be readily implemented by those having ordinary skill in this art.

Reference should now be made to Figure 5 which is a cross sectional view of an auxiliary heater for use with the system of this invention. As stated hereinbefore, certain jobs require.nozzles of a very large size, for example, 18 inches long by 3/4 inches wide by.7 inches deep. In such an instance, the solder -731- transferred into the nozzle may lose its heat to such a degree that the desired operation is compromised. Thus, to provide add4-tional heat to the solder once it reaches the nozzle, various implementations are possible. Thus, in Figure 1, auxiliary heaters indicated at 85 nay be disposed in the nozzle to provide the requisite auxiliary heat where means (not shown) could be provided to isolate the heaters from the solder. Another configuration for providing auxiliary heater is illustrated in cross section in Figure 5. The auxiliary heater comprises a solid block 200 of a material such as a metal or alloy which will store heat once it has been heated to a temperature such as the solder melt temperature. Disposed within the block are a plurality of heaters 202 which heat the block. An opening 204 extends through the block for the passage solder, the diameter of the opening being substantially the sane as that of opening 28 in nozzle 10. Plug 206 is attached to the bottom of block 200 and corresponds to plug 30 of Figure 1. Thus, it can be inserted in intermediate plug 34 of Figure 1 or into tubular portion 36 of cover 39. The upper surface of the block of solid material may be provided with a recess 208 for receiving nozzle 10. Other smaller recesses as indicated by dotted line 210 may be provided within the larger recess 208 to accommodate smaller nozzles. Moreover, detachable clamps indicated at 212 may be provided to clamp the nozzle tightly with respect to the block 208 and 'thus minimize or p-revent the flow of solder between block 200 and the underside of nozzle 10. Clamps 212 are diagrammatically indicated as being attached to the back side of nozzle 10 and engaging the underside of block 200 similar clamps (not shown) would be employed on the forward side of the nozzle. Since clamping means of various types are known, no further description is given with-respect to these elements.

Referring to Figure 6, another embodiment employing an auxiliary heater is illustrated. Here the nozzle 10 corresponds to that of Figure 1 and incorporated therein are heaters 85 as described above.. Additionally, a cap 214 is provided which is mounted over nozzle 10 to completely cover the upper opening thereof. Provided in cap 214 is a further nozzle 215 having an opening 216 which is smaller than the opening of nozzle 10. Thus, the embodiment of Figure 6 provides another means gor providing auxiliary heat to the work, if necessary.

Referring to Figure 2, there is diagrammatically indicated in dotted lines a diaphragm member generally indicated at 220. This diaphragm member may be inserted in the line between valve.78 and reservoir 12. The diaphragm member is divided into two air tight chambers 222 and 224 by a flexible diaphragm 226. Chamber 222 communicates with the upper surface 56 of.the solder in reservoir 12. Chamber 222, the confined space above surface 56, and the pipe connecting the latter space to chamber 222 are filled with an inertgas such as nitrogen.

Chamber 224 communicates with air pump 72 via solenoid valve 78 and needle valve 76. Due to the separation of chambers 222 and 224 from each other by diaphragm 226, there is no mixing of the air in chamber 224 with the inert gas in chamber 222.

Hence, no air comes into contact with the upper surface 56 of the solder in reservoir 12. Accordingly, diaphragm member 220 may be employed to further enhance the capability of the system of Figure 1 to provide a long lasting, substantially contamination-free operation. That is, the inert gas in chamber 222 will not react with the solder and thus the contamination level is lowered from the already low level established by the system of Figure 1.

In operation, pump 72 exerts air pressure against diaphracr= 226. Due to the flexibility of the di.aphragm, this pressure is transmitt-ted via the inert gas to the surface 56 of the solder in reservoir 12 to thus raise the solder to a desired level, as discussed above with respect to the Figure 1 ernbodiment.

Referring now to Figure 7, there is shown a further mode of operation of the system. As shown in Figure 1, the printed circuit board rests on the upper surface of nozzle 10. Since the walls 62 are thin and comprised of a low thermal conductivity, low thermal inass material, little heat is conducted from the walls to the underside of the board 20. Hence, there is little probability of damage to the board that will be caused by walls 62. In Figure 7, the board 20 may be slightly spaced from the walls to further minimize the probability of any damage thereto. Slight spacing of the board from the upper edge of nozzle 10 is possible since the solder can actually be raised to a position above the upper edge of the nozzle as indicated at 21. That is, due to the surface tension of the solder, it can be raised to the position shown in Fig-ure 7 without overflowing from the nozzle. Hence, spacing of the board from the nozzle can be readily implemented and yet effective soldering/desoldering can be achieved. Means for holding the board 20 in a given position with respect to nozzle 10 are disclosed in the related application Serial Number 763,704 mentioned hereinbefore.

As stated above, surface mounted devices may also be processed by the apparatus of the present invention. That is, the surface mounted device 256 may be simply inserted into the solder as indicated in Figure 7 for either desoldering a defective component from board 20 or soldering a new component thereto. Since the amount of time the solder is exposed to the work can be accurately controlled in accordance with the present invention, soldering of SMD1s to board 20 can be effectively achieved.

The method and apparatus of Fig-ure 1 is particularly suitable for various size jobs from the smallest to the largest, as discussed above. In the embodiment of Figure 8,-the method and apparatus is directed to smaller jobs and typically to jobs that have heretofore been manually performed with a soldering iron or the like.

An analysis of the typical hand soldering process utilizing a soldering iron (heated tip or bit), cored solder, and human skills reveals successful performance of the process is primarily dependent on the human skill factor, that is, the ability of the person to control various parameters of the Z process such as (a) thermal flow and limits, (b) solder feed, flow and limits and (c) all the other parameters of solder joint formation.

The degree of difficulty in the hand soldering process is directly related to the configurations and characteristics of the workpiece elements including such parameters as lead dimensions; pad or terminal access dimensions; through-theboard or surface terminations; the range and variations of the thermal characteristics and capacities of the various solder joints to be formed, the accessibility limits to the areas in which the solder joint is to be formed and last, but by no means least, the thermal and mechanical sensitivity of the workpiece components. Therefore, as the hand soldering process is applied to higher density assemblies, such a process becomes increasingly more difficult and demanding.

As stated above, the hand soldering process as presently practiced is primarily dependent upon human capacity while the soldering iron, the cored solder, etc. although essential ingredients play a relatively minor role in quality solder joint formation. This may be better understood by an analogy with the writing process. In the process of writing down a series of words the question may be asked what level role does the pen or pencil play as compared to the writer's role. Obviously the dominant role is that of the human being (well over 90%) while the pen or pencil merely makes the marks as directed by the human.

Based on this, one could conclude that the hand soldering process is morelikely to be over 90% dependent upon the human capability with the remainder dependent upon the devices, i.e., soldering iron, solder, etc. and that making a marked improvement on the process is more likely to be accomplished by improving the human factor and least likely to be measurably affected by improving the device, i.e., soldering irons with more precise controls, etc.

Therefore with the growing use of higher density assemblies and the associated degree of difficulty in soldering, it is the object of the Figure 8 embodiment of the present invention to provide a method and apparatus for performing the soldering process on individual and/or a plurality of solder joints so that the process is substantially less dependent upon human capability and substantially more dependent upon controllable devices than is the case with respect to soldering irons, etc., as discussed above.

In the Figure-8 embodiment, the principle of the manometer in combination with molten solder performs the equivalent of hand and/or machine (wave) soldering for forming individual solder joints or multiple solder joints on a broad. variety of work pieces while keeping the process controlled device dominant, with the human f actor being relegated to a more suitable and flexible role.

1 From the foregoing, it should be appreciated, the device of Figure 8 and equivalents thereof may be used in the place of soldering irons and, in fact, it is a further object of this invention to replace hand soldering irons in many applications with the device of Figure 8 and its equivalents.

Referring now to Figure 8, there is illustrated a preferred embodiment of the invention utilizing molten solder for procedures such as the soldering of individual and/or a plurality of solder joints although it is to be understood all embodiments of the invention may also be used for desoldering. As can be seen the pressurized air source 15 utilized wit-h the apparatus of Fig-ure I may also be utilized with that of Figure 8. Moreover, the device of Figure 8 in certain applications does not need the fast rise cycle of Figure 3. That is, the solder can be quickly and accurately brought to the working level of the solder at a desired rate of speed simply using the pulsation cycle of Figure 3. Moreover, as stated above with respect to other embodiments, the pressurized air source need not include means for pulsing the air source but rather the air may be directly applied without pulsation thereof.

The device includes a container 200, the walls of which are made of a material such as stainless steel and very thin in order to minimize heat conductivity and heat capacity and to promote physical portability. Since one of the primary intended uses of the Figure-8 device is bench top use where even individual joints may be soldered, the portability of the Figure 8 device is one of its important characterizing features. Container 200 may also be enclosed in a thermal insulation casing 202. Further heat insulating casings may also be provided as discussed below with respect to Figure 10. A tube 206 may be connected to an annular cover 208 where the tube 206 and cover 208 are also preferably made of a material such as thin stainless steel. Tube 206 projects into the solder and typically terminates about 0.10 inches above the bottom of container 200 to provide sufficient clearance for movement of solder into and out of tube 206, it being understood the above clearance may vary substantially depending on the application. The upper portion of tube 206 may be tapered as indicated at 210 to receive a plug 212 of a nozzle 214 the nozzle having an opening 216 which preferably is substantially the same size as the opening extending through plug 212. As can be seen in Figure 8, the lower outer edges of plug 212 are also tapered to permit a removable, force fit between the plug and tube 206 to thus effect a liquid tight seal for the molten solder 218 disposed within container 200 and tube 206.

To heat the molten solder to a desired temperature required for a job, a probe heater 221 may be provided at the bottom of container 200, the probe preferably projecting into tube 206 although it is to be understood other types of heaters may also be employed. Connection of the probe to an electric source 223 is diagrammatically indicated. As can be appreciated, the probe is in direct contact with the solder so that all heat goes to increasing the temperature of the solder and not the walls of the container.

Typical dimensions for the device of Figure 8 are as follows although it is to be understood the ranges given below are not intended to be limitative. Thus, the diameter of container 200 may be 1-3 inches with a preferred diameter being two inches. The height of the container may typically also be about 1-3 inches where a preferred height is also about two inches. With respect to tube 206, it may be about 1/4 to 1 1/2 inches in diameter and preferably about 1/2 to 1 inch in diameter.

Referring to Figure 9 there is shown a transverse cross sectional view take on the transverse line 6-6 of Figure 8 with the insulating casing 202 removed. The ratio of the transverse cross-sectional area of the container 200 as shown in Figure 9 to the tranverse cross-sectional area of tube 206 is preferably in the range of about 5:1 to 2:1 where the range may be as large as 10:1 to 1:1, the preferred ratio being about 3:1. Typically the amount of solder in container 200 is about 1/2 pound and is preferably less than 1 pound, although in some instances more may be used.

As can be appreciated from the foregoing, the device of Figure 8 with its smaller size and smaller weight is substantially more portable than that of Figure 1 and thus lends itself to bench top repair including that in the home. That is, the walls of reservoir 40 of Figure 1 device are made of cast iron or the like while those of Figure 8 device are preferably made of thin stainless steel or the like. Moreover, the amount of solder held by the Figure 1 device is 1 1 substantially more than that held by the Figure 8 device. Further, the ratio of the area of the cross-sectional area of container 40 of Figure 1 to the cross-sectional area of passageway 37 is typically 20:1 whereas the ratio is substantially less in the Figure 8 embodiment, as discussed above. Thus it can be seen from these differences and the other differences discussed above, the device of Figure 8 is eminently suited to replace the standard soldering iron while that of Figure 1 is not. Of course, the device of Figure I has its own uses and advantages in industrial applications where mass production and large scale jobs are the norm. However, for the smaller scale, sporadic uses which typifies some soldering iron usage, the device of Figure 8 is very suitable. Moreover, the device of Figure 8 can also be u sed on a mass production basis especially in those applications where soldering irons are used on a production-line basis.

Thus, it is the intent of the Figure 8 embodiment and its equivalents to replace the soldering iron in most or all present day usages thereof. With the replacement come s the improvements discussed above where the soldering process may be performed in such a manner on individual and/or a plurality of solder joints such that the process is substantially less dependent upon human capability and substantially more dependent upon a controllable device. In particular, the device of Figure 8 is substantially more controllable than a soldering iron. That is, the heat delivered to the joint(s) to be soldered is delivered by the same medium, that is, molten 1 solder which is used to form the joint. Accordingly, the temperature of the medium can be substantially more precisely controlled than the tip of a soldering iron and the cored solder which must be used therewith. Moreover, the cored solder is eliminated, this, of course, following from the fact that the solder of the Figure 8 device performs both the function of transferring heat to the joint plus providing the material for forming the joint.

Referring to Fig-ure 10, there is partially illustrated a further embodiment of the invention where the tube 206 extends above cap 208. Although in this embodiment, the upper inner edge of tube 206 may be tapered to receive a nozzle, it also may not be tapered as shown in Figure 10. In this embodiment, the configuration 220 of the upper end of 206 is typically circular and may be adapted for soldering/desoldering of individual joints. Moreover, the tube nay be connected to a capillary tube as discussed below with respect to Fig-ure 20. However, although not shown, the config-uration of the upper end of tube 206 may be specialized and adapted to a particular configuration such a that of a D.I.P. package, etc. Typically, the height of tube 206 above cover 208 is about 1/8 to 3/16 of an inch so that the solder stays hot, that is, the more tube 206 extends above container 200, the more heat is lost through the walls of the tube. In this regard, a heat insulative casing 225 may be provided around the portion that extends above cover 208. Moreover., a heat insulative casing 227 may also be provided above cover 208 where, of course, such a G casing for the cover may also be used in the other embodiments of the invention.

Referring now to Figures 11A-11C, 12A-12D, 13A-13C and 14A-14C, there are illustrated cross-sectional and plan views of possible config-urations of nozzle 214 of Figure 8 or the upper end 220 of the Figure 10 embodiment, there being no intent to be limited to the particular config-urations shown in the above f igures. Thus, in Figures 11A, 12A, 13A and 14A are shown illustrative nozzle cross-sectional views where the cross-section is taken in the plane of the cross-section of nozzle 214 of Figure 8. In Figures 11B and 11C are shown possible plan views which may correspond to the cross-sectional view illustrated in Figure 11A. In Figures 12B, 12C and 12D are shown possible plan views which may correspond to the crosssectional view illustrated in Figure 12A. In Figures 13B and 13C are shown possible plan views which may correspond to the cross-sectional view illustrated in Figure 13A while Fig-ures 14Rand 14C are possible plan views corresponding to the cross-sectional view of Figure 14A. From the foregoing, it can be seen a large variety of configurations of nozzle 214 or upper end 220 of tube 206 can be implemented for various special purpose applications. Another such application is shown in Figure 15A wherein the plan view of the openings 217 is conf -c Lg-ured in a unique shape such as that suitable for a transistor.

In operation, controlled air or gas pressure is provided from source 15 so that the molten solder is elevated to and maintained at the reference working level 226 of Figure 8 and, in particular, the fine meniscus level of Figure 15B. The gas or air pressure nay also be cyclicly strobbed with pulsating pressure by source 15 while maintaining the meniscus level thus creating minature scrubbing action to enhance film and tension breakdowns at the surfaces to be soldered to thus improve solder beating and enhance wetting action.

Figure 16 represents a cross section of a plated-through-hole work piece 228 and component lead 230 which together with the molten solder heating create surface tension forces and capillary forces which will cause the solder to flow upward, opposite gravity, and fill the hole 232 as well as cover metal surfaces 234 of the joint while maintaining an appropriate temperature of the molten solder and the metal surfaces within the joint so that the appropriate solutions of solder joint formation occur to connect lead 230 to the workpiece. As the meniscus is disturbed by the flow action due to the joint capillary surface tension, the additional solder moves up to create a new manometer balanced meniscus; thus very precise solder flow and metering occurs.

In Fig-ure 16, board or workpiece 228 is positioned so that the meniscus is in balance with the bottom of the workpiece. Another set-up position is illustrated in Fig-ure 17 where an imbalanced meniscus is established, that is, one whose natural height is above the workpiece bottom surface but still within the workpiece vertical dimensions thus creating an additional aiding force to overcome gravity while adding to I.

lt solder joint's surface tension and capillary forces without forcing the solder to create an undesirable overshoot on the top side 236 (component side) of theworkpiece. If necessary to provide greater forces, the natural meniscus height can even be set above the topside 236. Moreover, in the foregoing set-up or that of Figure 17, the board 228 may be positioned on the top of nozzle 214 as shown in Figure 17 where in Figure 17 it is assumed the thickness of the board is greater than the natural meniscus height.

In general, molten solder can, via the nozzle system, be provided to the workpiece in different patterns as discussed above with respect to Figures 11-14. Moreover, static meniscuses can be provided at the bottom workpiece surface (Figure 16) or even below the bottom workpiece surface or dynamic meniscuses can be provided above the bottom workpiece surface (Figure 17). Further meniscuses may be established to effect surface mount solder joint formations as well as the through-the-board solder joint formations of Figures 16 and 17. In a surface mount solder joint formation, the component itself is inserted in the solder for a brief period of time4 In the embodiments of Figures B-17, the tube 206 or the nozzle 214 is vertically oriented. In other embodiments of the invention, such as those of Figures 18 and 19 such vertical orientation is not present. Thus, in the latter embodiments, the capacity to create low level force differentials via air or g s pressures with manometer effects is employed in conjunction with small diameter capillary force constrictions so as to provide a molten solder dispensing and soldering system utilizing a gravity aid. Thus, in Figure IS tube 238 is inclined and connected to tube 206 at 240 and terminated in a capillary tube 242 having an opening of typically 20 mils diameter to provide the desired capillary action. In Figure 19 a flexible metal hose 244 is connected to tube 206 and provided with a capillary tube 246 at the end thereof for dispensing molten solder. An insulated handle 248 is provided at the distal end of hose -244 to facilitate manipulation thereof. Due to the capillary size of tubes 242 and 246, there is a tendency for the molten solder to be restrained within tube 238 or hose 244 where other-wise the solder would exit if the opening were substantially larger due to the pressure differential. However, if the pressure differential is increased to exceed a threshold depending on the orifice size of the capillary tube, a small amount of solder can be dispensed from the orifice for soldering a joint or the like.

Referring to Figure 20, a capillary tube 250 may also be employed in the vertically oriented embodiments of Figures 8 and 10 as indicated in the. partial cross-sectional view of Fig-ure 20 to provide the effects of Figure IS and 19 embodiments.

In general, the present invention combines and enhances the natural capabilities of humans with engineered devices to create high quality flexible processes.

With respect to device control factors, thermal energy is stored and transmitted thru a controlled temperature molten solder medium thus providing a uniform thermal transfer and capacity mechanism regardless of shapes or thermal mass of the workpiece solder joint and automatically delivers the optimum amount of solder required by each and every solder joint within the workpiece. The soldering action occurs within the optimum temperature range and within the ideal time/temp. cycle.

With respect to human control factors, the operator positions the workpiece over the desired soldering action area as directed by indicating means such as the indicating means disclosed in aformentioned U.S-. application serial No. 763,704 (now U.S. Patent No. 4,659,002 granted April 21, 1987). Other indicating means may be a simple spot source of light 251 as illustrated in Figure 21 where a PCB 252 can be positioned over the nozzle 250 (for example, by appropriate means such that a single hole could be soldered). The operator next activates the soldering process cycle and observes the solder joint formation action on the component side of plated-through- hole 232 by noting proper melt through and fill and then concludes the cycle when satisfactory melt and fill have occurred. Thus the human can provide for the ultimate flexible control to suit the broadest workpiece variations.

Movement to clear workpiece obstruction can be accomplished by moving the workpiece. Thus the operator may be required to position the work in the horizontal and vertical planes or the device of Figure 8 (for example) may be moved in the vertical plane as part of a machine's cycle, thus simplifying the human role.

T The surface area of the molten solder in tube 206 should be kept reasonably large and close to the working end of the nozzle to sustain uniform molten solder temperature under load to enhance proper solder joint formation. Moreover a rapid cycle, short stroke is preferred whenever rapid movement and a short soldering cycle are required from joint to joint. In this regard, vertical movement of the Fig-ure 5 device may be incorporated in this sequence as needed.

In summary, several new features of the embodiments of Fig-ures 8-21 include:

a) the solder nozzles 214 are of smaller size and may be nozzles with one or more long thin openings for the removal or soldering of D.I.P. pads or the like; nozzles with a few small holes to handle specific components such as transistors; or, in the limit, a single hole nozzle for soldering individual pads on a P.C. Board.

b) control of the height of the solder column, the time cycle and temperature of the solder to create a repeatable process independent of an operator, which consistently ensures uniform solder joints.

c) the operator no longer has to make a judgement of the solder process, but merely locates a solder hole over the nozzle opening by means of a locating system, with an indicator on the toD side, for exanple, of the P. C. Board.

d) a physically small solder container 200 is employed where the container may be raised to bring the nozzle in contact with the underside of the P.C. Board. The solder would Y Z then flow automatically upward to bond the joint where a repeatable and predetermined solder cycle may optionally be employed.

e) The vibratory cycling of the solder via pulsing thereof promotes wetting and scrubbing of the surface.

As discussed above, conventional soldering has many limitations. The method and apparatus of the present invention, including the embodiment where the pressurized air is pulsed, may achieve-automatically a perfect'and repeatable solder joint. The molten solder may be brought up to the P.C.B. surface by mechanically raising the nozzle to contact the board or vice versa. The meniscus may flow via capillary action and surface tension into the hole, and can be obser-ved by the user on the opposite side of the P.C. Board. The action can be enhanced by using greater pressure to raise the meniscus to the upper surface of the P.C. Board. Solder can be kept ready by adjusting the pulse rate from one which keeps it just below the nozzle surface to one which creates the meniscus. An important advantage is the repeatable control of the solder process with a system which has a known temperature coupled to a rapid thermal transfer medium (the molten solder) which can be applied to a joint(s) for a known and repeatable amount of time.

J T 1Q CLATMED-IS:

1. Apparatus for performing an operation on a workpiece with molten solder, said apparatus comprising a substantially encloseC molten solder container, a contained space being disposed within the..container above the molten solder; a tube for conveying the molten solder In the container to the workpiece where the ratio of the transverse cross- sectional area of the container to the transverse cross-sectional area of the tube is no more than about 10:1; and a source connected to said contained space for introducing a pressurized gas into the space to raise the solder through said tube to a predetermined level adjacent said workpiece and maintaining said solder at taid predetermined level to thus effect said operation with the molten solder.

Claims

2. Apparatus as in Claim 1, wherein said ratio is not less than about 1:1.

3. Appafatus as in Claim 2 wherein said ratio is in the range of about 5:1 to 2:1.

4. Apparatus as in Claim 3 wherein said ratio is about 3: 1.

1 -so- 1 0 5. Apparatus as in Claim 1 where said container is cylindrical and the diameter thereof ranges from about 1 to 3 inches.

6. Apparatus as in Claim 5 where said diameter is about 2 inches.

7. Apparatus as in Claim 5 where said tube is cylindrical and the diameter of said tube is about 1/4 to 1 1/2 inches.

8. Apparatus as in Claim 7 where the diameter of said tube is about 1/2 to 1 inch.

9. Apparatus as in Claim 5 where the height of said container is about 1 to 3 inches.

10. Apparatus as in Claim 1 where the weight of said molten solder is less than about one pound.

11. Apparatus as in Claim 1 where the walls of said container are made of stainless steel.

12. Apparatus as in Claim 1 including a heater for the molten solder, said heater being in direct contact with the solder.

13. Apparatus as in Claim 1 where said tube projects above the top of said container.

14. Apparatus as in Claim 1 where said source of pressurized air includes means for continuously turning the pressurized air on and off where the on period is greater than the off period to thus raise the molten solder to said predetermined level.

15. Apparatus in Claim 1 including a nozzle w here said tube is adapted to receive said nozzle and convey the molten solder from the container to the nozzle.

16. Apparatus as in Claim 15 where said predetermined level is approximately at the uppermost level of the nozzle.

17. Apparatus as in Claim 1 where said predetermined level is approximately at the uppe=ost level of said tube.

18. Apparatus as in Claims 16 or 17 where said workpiece is a platedthrough-hole printed circuit board and where said molten solder forms a meniscus which extends above said predetermined level.

1 4 1 g- Apparatus as in Claim 18 where said printed circuit board is so positioned that the height assumed by said meniscus is in substantial contact with only the bottom surface of the printed circuit board so that the molten solder enters at least one plated-through-hole of the board by at least capillary action.

20. Apparatus as in Claim 18 where said printed circuit board is so positioned that the height assumed by said meniscus is between the bottom and top surfaces of the printed circuit board so that the molten solder enters at least one plated-through-hole of the board by at least capilliary action and the pressure of said pressurized gas.

_21. Apparatus as in Claim 18 where said printed circuit board is so positioned that the height assumed by said meniscus is above the upper surface of the printed circuit board so that the molten solder rises above at least one plated-through-hole of the board.

22. Apparatus as in claim 18 including means for locating the printed circuit board with respect to the tube.

23. Apparatus as in Claim I including a further tube connected to said tube extending into the container wheresaid further tube is disposed at an angle with respect to the latter tube and a capillary tube disposed at the distal.end of the 1 further tube for dispensing said molten solder in response to application of said pressurized gas to the molten solder.

24. Apparatus as in Claim 23 where said further.tube is non-flexible.

25. Apparatus as in Claim 23 where said further tube is flexible.

26. Apparatus as in Claim 1 including a capillary tube disposed at the distal end of the tube.

27. Apparatus as in Claim 1 where said workpiece includes a printed circuit board and a component to be connected to or disconnected from the board and where the configuration of the nozzle or the upper end of said tube substantially conforms to the component.

28. Apparatus as in Claim 27 where said component is an integrated circuit chip having a plurality of terminals disposed along at least two side thereof and said nozzle or the upper end of the tube has a plurality of openings where the configuration of the openings conforms to that of the terminals.

1 29. Apparatus as in Claim 27 where said component is a transistor of the like having a plurality of terminals and said nozzle or the upper end of the tube has a plurality of openings where the configuration of the openings conforms to that of the terminals.

1 30. Apparatus as in Claim 17 where said nozzle or the upper end of of said tube has a single opening adapted to individually process one or more leads of said component.

31. Apparatus as in Claims 16 or 17 where said workpiece is a printed circuit board with a surface mounted device disposed thereon where the device is disposed within said molten solder.

32. Apparatus as in Claim 14 where said molten solder effects a scrubbing action at the workpiece due to the turning on and off of the pressurized air.

33. Apparatus for performing an operation on a workpiece with molten solder, the apparatus being substantially as hereinbefore described with reference to the accompanying drawings.

ous. 66571 High Holborn, Lond,)n WC1R 4TP. Ftirther copies rcky be)btained Published 1988 at T-he Patent Offim State H Ise. 66 from The Patent Office.

Sales Branch, St Mary Cray, Orpir4tm Kent BR5 3RLD. Printed Iy Multiplex techniques ltd. St Mary Cray. Kent Con 1187.