Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~2
77
1 UNITED STATES PATEWT APPLICATION
2 Of: Ronald Morino
For: SHOP~T PULSE SOLDERING SYSTEM
6 This invention relates to solderin~ ~nd, more
7 particularly to method and apparakus for short pulse soldering
& suitable for automatic wiring equipment.
q
Back~round of the Invention
11 The technology for production of circuit boards for
1~ interconnecting electronic components has advanced considerably
13 in recent times. The advance in integrated circuit technology
i4 has brought about ever increasing densification of electronics
which in turn has brought about an ever increasing demand for
16 denser and more reliable circuit boards for interconnecting the
17 Componen~s.
18 According to one highly successful technique, dense
lg circuit boaràs are created by scribing or writing wires on the
surface of the board using very fine insulated copper wire.
21 The wires zre deposited according to a computer generated
22 program. The wire pattern is thereafter encapsulated and the
23 end~ of the wires are connected to terminal pads on the board
24 surface. The technology is generally described in U.S. patents
3,674t602 and 3,674t914. ~ne of the significant advantages of
26 the wired circuit boards over conventional printed circuit
27 technology is that the lnsulated wires can cross one another
2~ and therefore very dense connection boards can be made in a
single layer thereby eliminatins the need for interlayer
connections.
-
~Z~,3~
l In the past, the connection.s to terminal pads in the
2 ~ired circuit boards has usually been accomplished ~y plating.
3 After the wire pattern is deposited and encapsulated, ~oles are
4 drilled throuqh the board at appropr:iate locations and then
plated. The hole plating is done in a manner that not only
6 plates the hole and forms the terminal pad, but also so that
7 the end of the insulated wire exposed ~y the drilled hole is
8 electrically connected to the pad.
9 ; Soldering techniques have, of course, long been used
to connect wires to terminals. However, such soldering
11 techniques have generally not been regarded a use~ul in high
12 speed automatic production of circuit boards because o~ the
13 1 difficulty in keeping the solder joint localized, because of
4 the need to avoid heat damage to the plastic board substrates,
1~ and because of the danger af solder entering the holes
16 associated with the terminal pads.
17 There have been prior attempts at solving these
18 pro~lems, such as:
l9 ~ ~a) con~iguring the solder pads to provide a
20 l narrow heat transfer restr$ction, between the solder area
21 and the plated hole (Stranco US patent 3,573,~81);
22 (~) providing an electrically conductive, heat
23 1 resistive nickel layer under the solder regions
24 (Stranco U.S. patent 3,673,681);
25 ' (c) cooling the soldering area wi`tb the flo~ of
2~ air or lnert gas`~(Stranco U.S. Patent 3,673,681, ~arsen ~.S.
~7 patents 3;650,45D and ;3!812,581):
28 (d) prestripping the segment o wire to be
29 soldered so that the solder joint nee~ not be subjected to high
temperatures required for insulation stripping (~icholas ~.S.
2--
~2~3~7
patent 4,031,61~);
(e) using parallel gap soldering where the
heat is generated at the solder surface by using thl' solder
pad to comple-te an electrlc heat generatincl circuit (Mulchay
U.S. pa-tent 3,~44,347); and
(f~ controlling the heat generated by ns;rlg
-temperature measurements -to con-trol the electric current
generating the heat (Denney U.S. patent 3,77~,5~1).
Although by using a combination of the above
teachings it is possible to produce satisfactory solder
joints, these techniques do not provide a system cap~)le of
tolerating the range of variations and conditions enconlltered
ln commercial production. I~lso, some of the methods
accordillg to the prior ~rt techrliques enulllerated above add
considerable cost and complexity to the operation or require
special board configurations which reduce -the board's
surface area available for routing wires.
Sumrnary of -the Invention
In accordance with this invention it has been
found, surprisingly, that there is a combina-tion oE conditions
and hardware capable of soldering very fine insulate~l wires
to terminal pads under the wide range ofl conditions normally
encountered in commercial production without darnaging the
substrate or the plated holes, without requiring special
circuit board configurations and without significantly
increasing costs.
The invention relates to a high s~eed me-thod of
operating in the presence of solder melting at about 450 F
for solderlng wire lying across a terminal pad or the like
on a circuit board, using a soldering tool of prede-termined
mass, comprising: (a) selectirlg the efEecl:ive mass (-~ lle
soldering tool so tha-t -the quan-tum of heat energy stored
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therein is only slightly in excess of that required for
an effective sol.der joint of solder meltling at about
450 F and is swbstantially used ~Ip during formation oE
the solder joint; (b) heating the effective rnass to a
preselected high ternperature below that which would cause
rapid deterioration of the tool;(c) bring:ing the tool into
thermal contact wi-th the wire to be soldered when lying
across the terminal pad; (d) while in thermal contact
(i) substantially imparting just enough heat to tlle W:i:l e
and the terminal pad to complete a solder joint, and (ii.)
permitting solidification oE the solder; (e) t-.he q~lantllm
of heat energy being insufficient to permit signi.ficallt
heat m:Lgration into the circu.it board beyond the t~rm:Lnal
pad; and (.E) wlle:rein the solderillcl tool :ls raisecl l..o a
temperature selected so that -the solder joint ~5 Eormed
in less than 500 milliseconds.
In another aspect, the invention relates to a
high speed method of soldering insulated wire lying across
a terminal pad of a circuit board coated with solder
melting at about 450 F using a heated soldering tool,
comprisillg: (a) selecting the ef:Eect:ive IIIclSS o:E tlle
soldering tool so that, when heated, the quantum of heat
energy which can be imparted for making a solder connection
is just sufficient :to vaporize insulation off the wire
and -to liqueEy -the solder melting at about ~50 ~ to make
an eEfec-tive solder joint; (b) hea-ting -the soldering tool
-to a temperature at leas-t in excess of the vaporizing
tempera-ture of -the insulation on the wire; (c) bringing
the soldering tool into contact with -the insulated wire
lying across the solder coated terminal pad; (d) the heating
period for the soldering tool, and the temperatllre the:reof
when heated, being selected to provide a temperature profile
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kh/ ~
Z~377
such that (i) the temperature imparted to the insulation
in the contact area exceeds the vaporization temperature
thereof, (ii~ l:he temperature of the solder on the pre-
sol.dered terminal pad exceecls the liquefaction temperature
of about ~50 ~ for a minimum period of time sufficient
for an effective solder joint and (iii~ the temperature
of the circuit board in -the vicinity of the terminal
pad does not rise above the temperature causing deterior-
ation thereof.
In its appara-tus aspect the invention relates
to a system operating 1n the presence oE solcler :Eor
soldering wire to a terminal pad on a circuit boa:rcl,
comprising: (a) a solder.lng tool havincJ a p.rodelor~l.rled
eEEective mass; (b) means for applying the:rmal energy to
the soldering tool (i) to raise the temperature of the
soldering tool to a preselected high temperature below
that which causes rapid deterioration thereof, and (ii)
to store in the soldering -tool a quantum of heat energy
only slightly in excess of that required for an effective
solder jo:Lnt and which is substantially used up during
formation of a solder joint; (c) means for br:Lnc3ing the
soldering tool into thermal contact with the wire to be
soldered while lying across the terminal pad (i) to
imp~rt jus-t enough heat to complete a solder joint~ and
(ii) to permit solidification of the solder; and (d)
the effective mass and the application of thermal energy
there-to being so selec-ted that the solder joint is formed
in less than 500 milliseconds.
An essentia]. aspect of the inven-tion is -to
control both the peak temperature of the soldering tool
and the quantum of heat made available during a soldering
operation. The
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Q377
1 ; quantum 'Qf heat i~ a function of the temperat~re o~ the
2 soldering tool, the mass of the soldering tool, and the
~ duration of energy application. The quantum of heat is
4 adju~ted so that it is just sufficient to provide,a reliable
5 1 solder joint under the range of conditions expected to be
6 encountered. It is important that the quantum of heat not
7 exceed the re~uired value. The peak temperature employed in
8 the solderins tool during the operation is quite high, above
9 lOOO~F and preferably in the range 1600 to 2000F. These high
temperatures are capable of vaporizing insulation o~ the wire
11 to expose the bare copper for soldering. Also, if the quantum
1 of heat and timing is properly controlled it is possible to
13 achieve a steep temperature gradient which confines the high
i~ ! temperatures to the regions where th~y are useful in stripping
insulation and melting solder while at the same time avoiding
16 high temperatures where they would be harmful. By controlling
17 the quantum of heat applied and the time of energy application,
18 the wire can be stripped and soldered before there is
19 sufficient heat migration to raise the temperature in the
20 ; sensitive regions to a point where damage to the circuit hoard,
21 insulated wire or terminal pad would occur.
22 With the technique accordin~ to the invention the
23 soldering time is very short, below 500 milliseconds and
24 preferably less than 50 milliseconds.
25i With proper conditions and apparatus it is possible to
26 complete a solder connection in less than 50 milliseconds
27 durin~ which the peak temperature for vaporizing insulation off
2~ the wire exceeds 750F, the peak temperature availahle ~or
29 soldering the wire to the termina~ pad exceeds 450~, but the
~0 termperature in the substrate adjaoent the terminal pad does
37~
not e~ce~d 550F. ~y controlling the quantum of heat
applied and the timing of the operation, the high temperature
insulation removal and the soldering are completed and the
heat used up before the hea-t can migrate into areas where
damage would occur.
BrieE Description of the Drawinqs
Fig. 1 is a partial plan view and partial block
I diagram illustrating the system according to the invention;
Fig. 2 is a detailed drawing illustrating the
placement of wire on the circuit board and the soldering
tool associated therewith;
i ~ig. 3 is a perspective view showing the wire,
soldering tool, and terminal pad;
Figs. 4 and 5 are illustrations showing a completed
solder joint when made according to the invention;
Fig. 6 is a diagram showing the temperature profile
during a soldering operation;
Fig. 7 is a schematic diagram illustrating a
single pulse type control system for energizing the
soldering tool; and
Fig. 8 is a schematic diagram illustrating a
multiple pulse control system for energizing the
soldering too~.
Detailed Description
The soldering apparatus according to the
invention can be incorporated in an automatic circuit
board wiring machine as illustrated in Figs. 1 and 2.
Further details of the overall apparatus are disclosed
in U.S. patents 3,674,602 and 3,674,914.
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~ kh/~ 3~ )
77
1 A circuit board ~ is mounted for movement by an X- Y
2 transport 40 and is moved from point-l:o-point according to a
~ ; computer control 42. A wire guide unit 10, scribing stylus 2
4 and soldering tool 30 are mounted above the circuit board so
5 , they can rotate as a unit. Insulated copper wire 11 is fed
6 1 tllrough the wire guide toward stylus 20 which presses the wire
7 into the tacky surface coating 6 on the circuit board as is
8 best seen in Fig. 2. The rotational position of the scri~ing
q unit (including wire guide 10, stylus 20l and soldering tool
30) is determined in accordance wi~h the direction of the table
11 movemènt so that the wire is laid down on the board surface as
1~ the board moves away from the scribing unit.
13 l, The soldering tool is pivotally mounted with respect
14 ~ to a pivot 31 so that it can be raised and lowered by a
15 ~ suitable solenoid or pneumatic actuator 48. When lowered into
16 the soldering position (shown in solid lines in Fig. 1) the
17 soldering tip 32 straddles the wire being laid down. A
18 soldering operation is normally performed while the table is at
, .
19 ` rest at a point where the wire overlays a terminal pad area to
20 ,, which the wire is to be connected. The terminal pad is
21 preferably pretinned and thus, when the appropriate heat is
22 applied the insulation is stripped and a solder joint is
23 completed.
2~,~ A position sensor 44 is attached to the X-Y transport
40 to sense the table position and determine when it is in the
i
26 proper posltion for the soldering operation. Wken in the proper
~7 position compu~er control unit 42 provides activation sign~ls
28 for a solenoid control unit '49 and a timer control unit 45.
29 Solenoid control unit 49 is connected to solenoid 48 and raises
and lowers soldering tool 30. A high current power supply 52
3~7
1 is connected to soldering tool 30 via a switching circuit 5~,
2 the switching circuit in turn being controlled by timer control
3 unit 46. The timer control causes one or more high current
4 pulses of predetermined enersy content to be applied to the
S soldering tool when called for by somputer control 42.
6 Details of soldering tip 32 o~ the soldering tool
7 stradling wire 11 an~ located over a terminal pad is as shown
8 in Fig. 3. The terminal pad can be formed by pressing a
9 pretinned hollQw copper ter~inal into circuit board 5 at the
proper location or by using printed circuit techniques to
ll copper plate a drilled hole and by subsequently tinning the
1' plated surface. ~he completed terminal pad 40 include~s a
13 ~! cylindrical body portion 42 passing through the hole and a
14 surface ~lange portion 41.
lS Tip 32 of the soldering tool has a generally ~-shaped
i6 cross section with the bridge portion o~ the "~ being the
17 effective mass of the tool. Tip 32 is preferably made of
18 tungsten. allo~s which are only slightly oxidized at high
l9 temperatures. In some cases it ma.y be desirable to carry out
20 l the soldering operation in an inert atmosphere to avoid
21 oxidation of the soldering tool. The bridge portion of the
22 soldering tool preferably has a groove on the lower surface
23 dimensioned to partially accommodate the wire ll being soldered
24 to maintain good thermal contact. The dimer.sions of the
2~ effective mass are "W", the width between tbe leg portions 34
26 and 35 o~ the tip, "Ln, the length in the direction of the
27 wire, and ffH~ the height of the bridge port.ion. The legs 34
and 35 of the bridge po~tion are integral with ~upport arms 3
29 and 37 secured in a suitable mounting str~cture 38 (shown in
Fig. l).
_ 7 _
~P~i377
1 ` A typical solder joint appears as shown in Figures 4
2 1 and 5~ The hole through body portion 42 of terminal pad ~0 has
3 a diameter of .04 inch, the radial dimension of flange 41 is
--4 j .015 inch and the outside flange diam~ter is .07 inch. The
5 I copper flange is .002 inch thick. The insulated wire ll
6 1l includes the copper wire with a ~004 inch diameter surrounded
7 , by insulation which is .0005 inch thick.
8 1l The solder layer is about .0015 inch thick. The
q 1I solder ~`illet 50 which joins the stripped wire to the terminal
10 `` pad is about .015 inch wide and .040 inch long.
11 Preferably the solder for the solder joint is supplied
17, by a solder coating on the terminal pad which can be a
13 ` pretinned coati~g as mentioned above, or a plated
4-j (non-eutectic) coating._ Alternatively, the wire can be solder -
lS coated to supply solder for the joint. Other techniques for
16 supplying the solder can also be employed. For example, solder
17 , in a powder or paste form can be ejected into the solder joint
18 ~ area, preformed solder in the shape of washers, disks, or
l9' ribbons can be placed in the solder joint area, or solder in
the ~orm of microdots or microspheres can be used.
21`
22 he Method According to the Preferred Embodiment
l !
In accordance with the invention the quantum of heat
24 utilized in a soldering operation is carefully controlled. The
,~ !
25 !, quantum o~ heat depends on the effective mass o~ the soldering
26 tool, the temperature of the soldering t~ol, the energy applied
27 during the so1dering operatiQnl and the mass of the wire and
28 copper foil forming the terminal pad on the circuit board.
29 The soldering tip tamperature is also con~rolled to
achieve a desired temperature profile so that maximum hea'
--8--
77
.
l energy is available for completing the solder joint and so that
2 there is minimum heat migration into the areas of the board
~ sensitive to heat.
4 Conditions-are selected to achieve rapid soldering
since, when constructing a circuit board by point-to-point
6 wiring, the time efficiency can be very important to the
7 realization of an effective wiring machine.
8 The selected conditions should permit the apparatus to
4 make good solder connections resardless of the surrounding
ln structure on the board. In commercial circuit board operations
l1 the size of the terminal pads may vary and ~n many cases are
12 associated with, or are near to, sizable ground planes. The
13 size of the copper area in the soldering r~egion affects heat
14 dissipation and heat migration. According to this invention,
condltions can be se~ected which will provide a good solder
16 joint for the broad range of conditions normally encountered in
17 a circuit board. In order to arrive at the appropria~e set of
18 conditions a series of experimental runs were made utilizing
19 soldering tools o different dimensions and energizing these
20 I tools at different ener~y levels and different periods of
21 time. The results of these tests are summarized in Table I
22 belo~
23
24
26
27
29
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1 The tool dimensions are in terms of the width, height
2 and length ~W x H x L) for the effective mas~ on the soldering
3 ` tool as indicated in Fig. 3. Thus, for example, the dimensions
4 ; in the first line o~ Table I indicate a width of .022 inch, a
5 1 height of .012 inch and a length of .32 inch for a total volume
6 of effective mass of 5.28 x 10 6 in3. The voltage applied
7 to the tool is 4.25 volts which results in a current of 175
8 amperes.
g T3 test the operation over the range of conditions
10 ; likely to be encountered in commercial circuit board
11 operations, tests were conducted on standard board
12 ; configurations using a relatively small terminal area in the
13 form of a 0030" wide strip and relatively large terminal area
14 ~ in the form of a 1 inch wide strip. Tests on these str1ps
represented approximately a thirty to one ratio of width and,
16 ~ hence, simulated the broad range of conditions encountered in
17 commerical operations. Tests were then run using different
18 ` soldering times for the various conditions and thereafter
19 inspecting and visually judging the solder joint.
20 ~ The conditions that resulted in acceptable solder
21 ' joints are set forth in Table I. For example looking at the
~2 second line of the t~ble, a soldering tool with an effective
23 ma~s volume of 5.28 x 10 6 in3 is energized with 6.4 volts
24 resulting in a 250 ampere current flow through the tool. On
the smaller strip (.030 inch width) an acceptable solder joint
26 was achieved using energization periods between 11 and 14
27 milliseconds~ For shorter energization periods ~in this case
2~ less then ll milliseconds) there was insufficient heat for
29 abl~tion of the insulation or insufficient heat to form a good
3~ solder joint. Longer energization periods ~in this case
~1'2~37~
1 greater then 14 milliseconds~ resulted in damage to the
2 substrate or dama~e to the insulation on the wire outside the
~ ~ solder area. Tests run with resp~ct to the larger strip (one
4 l¦ inch width) determined that acceptable solder joints were
S ¦i achieved using an energization period between 12 milliseconds
6 1 and 23 milliseconds. Thus, in the range between 12
7 ~ milliseconds and J4 milliseconds, using this particular size
8 ,ll tool, acceptable solder joints are achieved regardless of
q ~ terminal pad size, i.e. in the range from ~030" to 1".
-The temperature of the tool was determined visually by
11 l observing the incandescent color and estimating the
12 ll corresponding temperature. For the second line of Table I the
13 ~l tool temperature was estimated to be 1830F from the bright
14 cherry-red color.
This series of experiments es~ablish that there are
16 conditions which can be selected for makin~ satisfactory solder
17 joints over the range o~ conditions encountered in normal com-
18 mercial operations. As indicated on lines 2 and 3 of the
19 table, if the soldering tool mass is relatively small
20 l' (corresponding to an e~fec~ive mass volume of 5.28 x 10-6
21 ll in ) and the tool is energized with a potential of 6.4 or 8.6
22¦~ volts with corresponding current 10ws of 25G and 275 amperes,
23 1I then energization periods exist which will sati~y the full
24l range of board conditions. At the lower potential of 6.4 volts
25~ (corresponding current of 250 amperes~ an energization period
26 of 12-14 milliseconds resulting in a tip temperature of 1830F
27 produces acceptable solder joints over the range of terminal
28 pad sizes. hikewise, at the somewhat higher potential of 8.6
29 volts (corresponding current of Z75 amperes) an energiæakion
period in the range of 6-8 milliseconds at a corresponding
-12--
37~
1 soldering tool temperature of 2000-2200F also achieved
2 acceptable solder joints over the range of terminal pad sizes.
3 j As can be seen from Table I, where the ran~e of
' terminal pad sizes is narrower or where all terminal pads are
S ll, of a uniform siæe, o~her conditions can be found that produce
6 ,,, satisfactory solder joints. It should be noted that in all
,, :
7 ; cases the energization period is less than 500 millisecunds and
8 thus provides a rapid soldering technique useful in automatic
4 il machinery. In mos~ cases satisfactory solder joints are
ln achieved using energization periods less than 150 milliseconds
11 and in many cases beIow 50 millisecônds. I
12 Although in a few cases acceptable solder joints have
13 ll been made at low soldering tool temperatures, in general, the
1~ l tool temperature should be above 1000~ and preferably in the
15 I range of 1600 to 2000~F. Lower solderin~ tool temperatures
16 require longer soldering times and ener~i~ation perjods and
17 result in greater heat migration into the substrate of the
1. .
18 circuit ~oard. Higher temperatures generally provide a steeper
1~ temperature gradient with less heat migration and shorter
energization periods and contact times. Temperatures above
21 2000F, however, are undesirable because of the more rapid
22,, deterioration of the soldering tool at such temperatures.
23 Fig. 6 of the drawings shows a typical temperature
24 profile estimated for soldering tool temperatuxes above 100~F
25 ~ at approximately 1400~F. The tip 62 of soldering tool 58
26 presses insulated wire 68 down on copper foil terminal pad 64
27 ~located on plastic circuit board 65. The insulated wire is
28 shown after ablation of the insulation in the solder joint
29 area. The wire is shown soldered to the copper foil pad bv
~ shown in Fi~ures 4 and 5
solder fillet 5~~ A solderin~ temperature of 1400F is
-13-
~ ~ p! ~ ~
1 / provided by a tool having dimensions .022 x .016 ~ .02 (7.04 x
2 ~ 10 6 in3) energized by 6.5 volts (current of 250 amperes).
An energization period of 22 milliseconds provides an
acceptable solder joint to a pad with a diameter of Ø07 inch.
I The soldering tool first vapori~es the insulation off
6 ~ the wire. The unstripped insulation outside the solder area
7 reaches a maximum temperature of about 700~. The copper wire
8 reaches a temperature above 750~F and approximately 900~F,
9 , i.e., a drop of about 500~F from the peak tool temperature.
ln l, The solder reaches a temperature above the melting point of
50F and normally about 530F which is a drop of about 370F
1' ' below the temperature of the copper wire. The temperature of
13 1, the copper terminal pad is close to that of the solder. The
pad temperature would normally reach & peak of about 500~,
15 ' approximately 30~F below the solder temperature/ and remains
16 ~ safely below 550F. The plastic in the circuit board would
17 normally reach a maximum temperatu~e of about 480F, about 20~
18 ,' below the pad temperature and, hence, would remain safely below
19l~ the temperature of 55CF where damage to the substrate occurs.
20 l Most of the solder inside the hollow portion of the terminal
21 pad stays below a temperature of about 350~ and, hence, stays
22 below the solder melting point of 450F.
23 l The temperature profile is important since it provides
24,l hi~h temperatures and heat energy where required for stripping
25' and soldering without providing excessive heat inside the
26 hollow portion of the terminal pad or in the circuit board
27 where damage could occurO ~igher tool temperatures (and
28 shorter energizaLion periods) tend to provide steeper
2g~ temperature gradients and, hence, more heat is available at the
soldering area without significantly increasing temperature in
-14-
2;377
1 areas where damage would occur. Of particular significance ls the
2 selection of conditions so that the quantum of heat supplied is
onl~ slightly in excess of that required for an effective
solder joint so that the heat is used up in making the solder
'! i
joint and does not migrate to areas where damage would occur.
6 In operation when the heated soldering soldering tool
7 first comes in contact with the insulated wire there is
8 relatively poor heat conduction. After the insulation breaks
q down, the soldering tool comes in contact with the copper wire
and the thermal resistance drops considerably. At this point
11 the wire in contact with the soldering tool is heated so that
1' the portion of the insulation between the wire and the terminal
13 pad can be removed. The heat remaining after removing the
1~ insulation must be sufficient to melt the solder and form the
lS solder joint. ~emperatures in excess of 7Q0F are required in
16 the ablation of the insulation whereas temperatures in excess
1 7 OI 450F are required to melt the solder.
18 The energy supplied to the tool should be DC or high
19 frequency AC and should be in the form of high current pulses.
20' Where o~ly a single electrical pulse is used in a soldering
21 operation, the current should be in the range of 50-500 amperes
22l and the pulse duration in the range of 500 to 5 milliseconas.
23 As previously indicated the two primary factors which
24 are controlled in accordance with the invention are the tool
temperature and the quantum of heat delivered. Generally the
26 too~ temperature ~hould be as high as possible but below the
27 temperature causing significant deterioration of the soldering
28 tool. The quantum of heat delivered to the soldering arear
29 which is a function of the tool temperature, the effective mass
of the tool and the energization period, should be only
-15-
7'7
1 slightly in excess of the amount of heat required for stripping
2 the insulation and completing the soldering joint. This
, objective can be achieved by constructing the soldering tool
having a certain mass and controlling the current and
5 ~¦ energizing the tool for a predetermined period while the tool
6 ~l is in contact with the wire being soldered. Proper control of
7 the ~uantum of heat applied can also be achieved by preheating
8 a preselected tool mass to store the correct quantum of heat
q and by then bringing the tool into contact with the solder
area. Also, appropriate control can be achieved by
11 combinations of prestored heat and energy supplied during
1~ contac~.
13 1, Preferably the soldering tool applies pressure to
1~ li maintain the wire in contact with pad area and stays in contact
15 1, until the solder solidifies. In this fashion the risk of wire
16 movement during solidification of the solder is minimized. In
17 , cases where the required quantum of heat is p~estored in the
18 i tool, the tool contact period is selected to achieve the heat
19 ~I transfer and also to include an appropriate cooldown period.
20 1~ Where energy is supplied during contact, the contact period
21 ' after completion of the energization period is controlled to
22 provide an appropriate cooldown period. Preferably the
23 , soldering tool is designed so that after the correct quantum of
24 , heat has been delivered to the solder joint the soldering tool,
while still in ~ontact, dissipates heat from the solder joint.
26 This can be achieved, for example, by including thermally
27 conductive support arms 36 and 37 (Fig. 3~ in thermal contact
28 with the effective mass 32 of the soldering tool.
2~ In some cases multiple energization has advantages.
For example, a first energization pulse may be supplied for
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1 stripping the insulation and a separate second pulse may
2 thereafter be supplied for soldering. A suitable two pulse
~ program sequence could include a first pulse at 6 volts for 8
4 miliseconds to strip insulation follo~wed by a second pulse at 4
S 1 volts for 25 milliseconds to complete the soldering joint.
6 With this arrangement there is a higher temperature (above
7 700) for stripping for a short interval followed by a lower
8 temperature (above ~50F) for a longer period ~or solderins.
q .
The Preferred Control Apparatus
11 ~s previously mentioned with regard to Fig. 1 the
1' control apparatus for the soldering tool generally includes a
13 power supply, a switching circuit and a timer control. A
1~ specific preferred system for single pulse soldering operations
is shown schematically in ~i~. 7.
16 As indicated in Table ~, short, high current pulses in
17 the range of 150 to 400 amperes are required. Although any
18 high current source can be used, a storage battery 70 including
19 up to four Gates BC cells manufactured by Gates Energy
Products, Inc., Denver, Colorado, provides a convenient low
21l, voltage, high current source. Each cell is rated at 2.0 volts
22 l and 25 ampere-hours. A conventional charging circuit 72 is
23 ' connected across the battery to maintain a f~ll state of charge.
2~ ~he switching circuit includes six NPN power switching
transistors 100-105, three NPN drive transistors 92-94 and an
26 initial transistor gO, also of the NPN type. The timer control
27 includes a controllable monostable multivibrator 82 and an
28 associated flip-flop circuit 80~
29 In the illustration, a switch 78 is shown for
3C initiating an energizing cycle. In an actual system switch 78
37~
1 may be the contacts of a relay in the control computer. The
2 normally closed contact of switch 78 is connected to the reset
input R of flip-flop circuit 80 and the normally open contact
is connected to the set input S. One of the outputs of flip-
S flop circuit 80 is connected to the trigger of monostable
6 flip-flop circuit 82. A variable resistor 83 and a capacitor
7 84 are connected ~etween the ~12 volt supply and the monostable
8 circuit to provide the timin~ control. The variable resistor
9 and capacitor have values selected to provide time intervals
between 5 and 500 milliseconds.
11 Each time switch 78 moves to the alternate position
1 , from that shown in Fig. 7, flip-~lop circuit 80 changes state
13 and produces a transient change at the out~ut. Monostable
14 circuit 82 responds to the transient change and produces a
15 ! positive pulse at its output having a duration determined by
,. ;
16 the se~ting of variable resistor 83.
17 The output of the monostable circuit is connected to
18 the base of transistor 90. The collector of transistor 90 is
19 , connected to the ~12 volt supply via a resistor 89 and the
emitter is connected to the ground. A bias resistor 88 is
21 connected between the base of transistor 90 and the ~12 volt
22 supply.
23,~' The collector of transistor 90 is connected to the
24 i base terminals of drive transistors 92-~4 and to ground via a
25 I resistor 91. The collectors of transistors 92-94 are connected
26 to the posltive terminal of battery 70 via variable resistors
27 96-98, respectively. The emitter of transistor g2 is connected
2~ to the base terminals of power transistors 100 and 101; the
29 emitter of transistor 93 is conne~ted to the base terminals of
power transistors 102 and 103; and the emitter o~ transistor 94
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3~7~
1 is connected to the base terminals of power transistors 104 and
2 105. The positive terminal of battery 70 is connected to one
3 arm 36 of soldering tool 30 and the other arm 37 is connected
4 to the common collector connection of transistors 100-105. The
emitters of transistors 100-105 are connected to the negative
6 terminal of battery 70 via fuses 110-115, respectively.
7 Variable resistors 96-98 are used to balance the drive and
8 power transistors circuits for a proper sharin~ of the load.
q A positive pulse at the output of monostable circuit
82 renders transistor 90 conductive which renders drive tran-
11 sistors 92-94 conductive which in turn render power transistors
1,' 100-105 conductive. When the power transistors are conductive
13 current flows from the positive terminal of battery 70 through
~ soldering tool 30 and then through the parallel paths of the
collector-emitter circuits sf power transistors 109-105 back to
16 the negative terminal of the battery.
17 Thus, actuation of switch 78 produces a high current
18 pulse through soldering tool 30 having a duration in accordance
19 with the setting of variable resistor 83. The amount of
current that ~lows through the soldering tool depends on the
21 dimensions and composition of the tool. Two cells in batte~y
22 70 provide a voltage somewhat above 4 volts and, with ~ools
23 dimensioned as indicated in Table I, current pulses in the
24 range o~ 160 to 250 amperes are produced~ With three cells the
potential is somewhat above 6 volts and current pulses in the
26 range of 250-325 amperes are produced. With f'our''cells the
27 potential is somewhat above 8 volts and the current pulses are
28 in the range of 275 to 425 amperes.
29 As previously mentioned, in some cases a multiple
pulse sequence is preferable such as 6 volts ~or B milliseconds
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77
1 for high temperature insulation stripping followed by 4 volts
2 for 25 milliseconds for completing the solder joint. A
suitable circuit for such a pulse sequence is illustrated in
Figure 8. In this case the energy for the soldering tool is
provi~ed by a three cell battery includin~ a pair of cells 121
6 in series with another cell 120. A charging circuit 122 is
7 connected across the battery to maintain the battery at a full
8 state of charge.
~ ~ Two power transistors lB0 and 181, in parallel, are
used to connect the four volt source to soldering tool 30 and
11 transistors 170-172 form the drive circuit therefor. Three
12 power transistors 160-162, in parallel, are used to connect the
13 ; six volt source to the soldering tool and transistors 150-152
~ form the associated drive circuit. A monostable flip-flop 130
forms timer ~ for controlling the ~ volt energization period
16 and a monostable ~ultivibrator 140 forms timer B for
17 controlling the 4 volt energization period.
18 Monostable circuits 130 and 140 have variable
19 resistors 131 and 141, respectively connected between the
circuit and the ~2 volt source. The variable resistors and
21l; associated capacitors 132 and 142 form the timing circuits for
22 the monostable multivibra~ors
23 An input terminal is connected to the trigger input of
24 circuit 130 and the output of circuit 130 is connected to the
25, trigger input of circuit 140. If resistors 131 and 141 are set
26 for 8 milliseconds and 25 milliseconds, respectively, then a
27 transient trigger signal on terminal 135 produces a positive 8
28 millisecond pulse at the output of circuit 130 followed by a
29 positive 25 millisecond pulse at the output o~ circuit 140.
The output of circuit 130 is connected to the base of
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2~377
1 NPN transistor 150 via resistor 153. The collector of
2 transistor 150 is connected to the *12 volt source via resistor
~ 154 and to the base or NPN transistor 151. The collector of
~ transistor 151 is connected to the +12 volt source via series
~ resistors 155 and 156 and the junction of the resistors is
6 connected to ~he base of NPN ~ransistor 152. The emitters of
7 transistors 150 and 151 are connected to ground whereas the
8 ' emitter of transistor 152 is conne~ted to the +L2 volt source.
q The collector of transistox 152 is connected to the ba~e
terminals Q~ NPN power transistors 160-162. The positive
11 terminal of battery 120 is connected to the common collector ~,
1~ ; circuit of parallel transistors 160-162, the emitters thereof
13 being re~urned to the negative battery terminal through fuses
1~ . 163-165, respe,ctively, and soldering tool 3Ø.
15 . The output o~ circuit 140 is connected to ground
16 ' through resistors 173 and 174 and the junction of the resistors
17 is connected to the base of NPN transistor 170. The emitter of
18,, transistor 170 is connected to the base of NPN transistor 171
19 and the emitter thereof is connected to ground. The collectors
or transistors 170 and 171 are connected to the ~12 volt source
21 through series resistors 175 and 176 and the junction of the
22 resistors i connected to PNP transistor 172. The emitter of
23 ' transistor 172 is connected to the +12 volt source and the
24 ~ collector thereo~ is connected to the base terminals of NPN 1,
power transistors 180 and 181. The positive terminal of
26 battery 121 is connected to the common collector circuit of
27 parallel transistors 180 and 181 and the emit~ers thereof are
28 connected to the negative battery terminal through fuses 182
29 and 1~3, respectively, and soldering tool 30.
A trigger pulse at terminal 135 causes monostable
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377
1 circuit 133 to pr~duce an output pulse which renders
2 transistors 150-152 in the drive circuit conauctive which in
3 turn renders parallel power transistors 160-162 conductive. As
4 a result, a high urrent pulse o~ a duration determined by the
5 ,` setting of variable resistor 131 is supplied to the soldering
6 tool from the 6 volt battery source 120-121. Termination of
7 the pulse at the output of clrcuit 130 triggers operation of
8 monostable circuit 140 which then produces an output pulse
q , which renders drive transistors 170-172 conductive which, in
turn, render parallel power transistors 180-181 conductive.
11 This results in a high current pulse being supplied to the
1' soldering tool via transistors 1~0-181 from the 4 volt source
13 ,l 121 for a period of ~ime determined by the setting of variable
14 I resistor 141.
While only a few illustrative embodiments have been
16 ~ described in detail, it should be obvious that there are
17 numerous variatlons within the scope of this invention. The
18 inven~ion is more particularly defined in the appended claims.
19
20,
21
22
23
~4 j
25'
26
27
28
29
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