FR2526624A1 - HIGH SPEED WELDING METHOD FOR WIRING - Google Patents

Abstract

THE INVENTION RELATES TO RAPID WELDING OF METAL WIRES TO PRINTED CIRCUIT BOARDS. IT RELATES TO A PROCESS ACCORDING TO WHICH A WELDING TOOL 30 HAVING A LOW EFFICIENT MASS BUT WELL DETERMINED, IS TAKEN TO A DETERMINED HIGH TEMPERATURE, PREFERREDLY BETWEEN 870 AND 1100C, AND TRANSMITS TO A WIRE WHICH MUST BE SUBJECTED 5 A BASIC AMOUNT OF HEAT JUST SUFFICIENT FOR AN EFFECTIVE WELD TO BE FORMED, WITHOUT THE INSULATION OF THE PAD RISING TO BE DAMAGED. THE HEAT IS PROVIDED IN A PULSE FORM FOR A PERIOD BETWEEN 5 AND 100 MILLISECONDS. APPLICATION TO AUTOMATIC WIRING OF PRINTED CIRCUIT BOARDS OF ELECTRONIC CIRCUITS.

Description

The present invention relates to welding, and more specifically to a method

  and a short pulse welding apparatus suitable for apparatus

Automatic cabling.

  Platelet manufacturing technology

  circuit for the connection of the electrical components

  tronic has progressed considerably in recent times.

  Advances in integrated circuit technology have led to

  increased densification of electronic circuits.

  which has itself led to the realization of larger and larger circuit boards denser and

  more reliable for connecting components.

  According to a very satisfactory technique,

  dense circuit trunks are formed by tracing or writing

  metal wires on the surface of the wafer

  using a very thin insulated copper wire.

  are deposited according to a program formed by ordina-

  The design of the metal wires is then coated and the ends of the wires are connected to connection pads formed on the surface of the wafer. This technology is described in French patents Nos. 2,084,258 and 2,400,304. One of the advantages important

  wired circuit boards with respect to the technology

  The classical logic of printed circuit boards is that isolated metal wires can overlap and as a result

  platelets with very dense connections can be

  in a single layer, without the connections between

layers are needed.

  Until now, the connection to connection pads has usually been made by depositing in the hardwired circuit boards After the deposit formed by the wires and its coating, the holes are drilled in the wafer at suitable locations, then This coating of holes is made in such a way that not only is the hole coated and forms the connection pad but also the end of the insulated wire, exposed by the drilled hole, is electrically connected.

at the connection range.

  Welding techniques have obviously been

  used for a long time for the connection of metal wires

  However, these techniques have not generally been considered as useful in the high-speed automatic manufacture of circuit boards because of the difficulty of locating the welded connection, since platelet substrates are difficult to locate. of plastic material should not be

  deteriorated by heat and because of the risk of penetration

  weld in the holes near the connection pads. We have already tried to solve these problems by

example:

  <a) by using weld connection pads having a configuration such that a shrinkage reducing heat transmission is foreshored between the weld area and the coated hole,

  (b) by placing a layer of nickel

  conductor of electricity but poor conductor of heat, under welded regions, (c) by cooling the welding zone with a current of air or an inert gas, (d) by stripping the section beforehand of solder wire so that the formed weld does not have to suffer the

  high temperatures necessary to remove the iso-

  (e) by using welding in parallel spaces, the heat being released at the surface of the weld, using the solder failure to close a heat generating electrical circuit, and f) by adjusting the heat released by means of temperature measurements to adjust the current

electric that releases heat.

  Although the use of a combination of these techniques makes it possible to obtain satisfactory welds, these techniques do not allow the use of a wide range of techniques.

  wide range of tolerances and conditions,

  actually in the course of industrial production.

  In addition, some of the methods implementing the techniques

  The above-mentioned known problems greatly increase the price and complexity of the operation or require special configurations of wafers that reduce

  the area available for routing the wires.

  It has been found according to the invention, quite surprisingly, that a combination of conditions and elements allowed the welding of very thin insulated wires.

  on connection areas under very different conditions.

  normally encountered during industrial production, without deterioration of substrate or coated holes, without the need for special circuit board configurations and

significant cost.

  The invention relates to a working method

  at high speed in the presence of welding intended for

  depositing a wire on a connection pad or the like formed on a circuit board, using a welding tool having a predetermined mass, the method comprising placing the tool in thermal contact with the wire solder and the connection pad and, during

  contact, transmission to the wire and to the

  practically the only amount of heat that is required for the formation of a weld, including the solidification of the weld, this method being characterized

  in that the effective mass of the welding tool is selected

  so that the amount of heat energy conserved only slightly exceeds the amount required to form an effective weld and this quantity is practically consumed during the formation of the weld, the method comprising heating this effective mass to a predetermined temperature so that the weld forms in less than 500 milliseconds, this temperature

  predetermined, however, being less than that which

  cause a rapid deterioration of the tool, this amount of heat being insufficient to cause a

  significant migration of heat in the circuit board

  cooked, beyond the connection range.

  An essential feature of the invention is the adjustment of both the peak temperature of

  the welding tool and the amount of heat available

  This amount of heat is a function of the temperature of the welding tool.

  welding, the mass of this tool and the duration of application

  energy cation This amount of heat is adjusted

  so that it suffices just for the formation of a

  reliable in the range of conditions that can be

  Predictably Controlled It is important that this elemental amount of heat does not exceed the desired heat. The peak temperature used in

  welding during operation is very high, higher

  than 5300 C, and is preferably between

  870 and 11000 C These high temperatures allow the vapo-

  wire insulation and the exposure of bare copper for welding.

  elemental heat and synchronization are

  It is possible to obtain a very steep temperature gradient which limits the presence of high temperatures to the regions where they are useful for wire stripping and weld melting, whereas high temperatures do not exist where they occur. could be harmful Adjusting the basic amount of

  applied heat and the duration of the application of

  It allows stripping and welding of the wire before the amount of heat that migrates is sufficient for the temperature of the sensitive regions to reach a value.

  may cause deterioration of the circuit board.

  cooked, insulated wire or connection pad.

  During the implementation of the techniques according to the invention, the welding time is very short, lower

  500 milliseconds, and preferably less than 50 milli-

seconds.

  Under conditions and with a device

  venable, a weld can be achieved in less than milliseconds, the peak temperature, allowing the

  vaporization of the insulation, exceeding 4000 C, the temperature

  peak temperature available for wire bonding in the range exceeding 2300 C, substrate temperature near the connection range not exceeding 2900 C, however. Setting of the amount of heat supplied and synchronization of the operation allows the removal of high temperature insulation and welding as well as heat consumption before it can migrate to areas in which deterioration occurs

can appear.

  Other features and advantages of the

  will become apparent from the following description,

  with reference to the accompanying drawings in which Figure 1 is a partial section partly in the form of a block diagram of an apparatus according to the invention; Figure 2 is an enlarged section of a detail showing the placement of the wire on the circuit board and the associated welding tool; Figure 3 is a perspective with parts

  snippets representing the wire, the tool of sou-

  age and the connection range; Figures 4 and 5 are respectively in plan and in cross section, the representation of a completed weld made according to the invention;

  FIG. 6 is a circuit diagram representing

  both a control circuit for exciting the welding tool with a single pulse; and Fig. 7 is an electrical diagram showing

  a control circuit for feeding the power tool

by several pulses.

  The welding apparatus according to the invention can be incorporated into an automatic wiring machine of

  printed circuit boards, as shown in Figures 1 and 2.

  Ato 6 t 4 Further details of the entire device are described

  in British Patent No. 1,593,235 and in the

  French vouchers Nos. 2,084,258 and 2,400,304.

  A circuit board 5 is mounted so that it can be moved by an X-Y transport device 40 and is moved from one point to another by a control 42 having a computer.

  guidance, a style of inscription or

  and a welding tool 30 are mounted above

  the wafer so that they can turn as a whole.

  A copper wire 11 which is isolated is transmitted by the guide-

  wire to style 20 that presses the wire against the coating

  superficial adhesive 6 worn by the plate as the indi-

  that more clearly Figure 2 The rotational position of the tracing assembly (including the wire guide 10, the

  style 20 and tool 30) is determined according to the

  moving the table so that the wire is deposited on the surface of the wafer when it moves away

of the tracing set.

  The welding tool 30 is articulated on a pivot 31 so that it can be lifted and lowered by an organ

  suitable for pneumatic or electro-pneumatic operation

  The welding tip 32, when lowered into the welding position (shown in solid lines in FIG. 1) is placed astride the deposited wire Welding is normally performed when the table is at rest at a point where the wire bears against a range to which the wire is to be connected The connection range

  is preferably pre-tinned so that, lo Vs-

  that a suitable quantity of heat is applied, the iso-

  lant is removed and the weld is executed.

  A position sensor 44 is attached to the X-Y transport device to sense the position of the table and determine when the table is in the position suitable for welding when the table is in position.

  the control 42 transmits excitation signals

  An electromagnet control assembly 49 and a timer control assembly 46. The assembly 49 is

  connected to an electromagnet 48 which raises and lowers the

  A welding power supply 52 of a current

  high voltage is connected to the tool 30 by a switching circuit 50 which is itself controlled by the assembly

  46 This timer control assembly causes the trans-

  mission of one or more pulses of a current of

  high intensity, corresponding to a predetermined quantity

  energy, to the tool 30 when the command 42

suggests.

  FIG. 3 shows details of the welding tip 32 of the tool 30 straddling the wire 11, above a connection pad.

  be formed by pressing a hollow copper terminal pre-

  tinned in a circuit board at the proper location or using printed circuit techniques for coppering a drilled hole, and then tinning the coated surface. The terminated range 60 of connection to a cylindrical body 62 passing through the hole and a part

  surface 61 forming a flange.

  The tip 32 of the tool 20 has a generally U-shaped section whose intermediate portion constitutes the effective mass of the tool The tip 32 is preferably made of a tungsten alloy which only oxidizes very little at all. high temperature In some cases it can

  it is desirable that the operation be carried out under

  inert gas so that tool 30 does not oxidize

  intermediate of the tool preferably has on its underside

  a throat whose dimensions are such that the

  welded wire 11 can be housed therein, with good thermal contact

  The dimensions which determine this effective mass are the width W between the branches 34 and 3-5,

  the length L measured in the direction of the wire and the height

  H of the intermediate part The branches 34 and 35 of the intermediate part are integral with the arms 36 and

  37 of support fixed to a suitable structure 38 of

floor (Figure 1).

  FIGS. 4 and 5 show an example of a weld made. The hole formed in the body 62 of the strip 60 has a diameter of 1.0 mm, the radial dimension of the flange 61 is 0.38 mm, and the external diameter of the flange is 1.75 mm The copper flange has a thick

  0.05 mm The insulated wire 11 includes a wire of

  0.1 mm diameter surrounded by 0.0125 mm thick insulation. The weld layer has a thickness of about -0.038 mm. The weld fillet 50 which connects the bare wire to the beach has a width of about 0.38 mm and a length

1.0 mm.

  Preferably, the solder used for the operation

  This is provided by the coating of the beach which may be a pre-tinned coating as previously indicated or a <non-eutectic coated coating. Alternatively, the wire may be coated with solder to give the

  welding required for connection Other techniques of

  the application of the weld can be used, for example

  In the weld region, weld or paste may be ejected into the welding region, weld preforms, for example washers, discs or ribbons, may be placed in the weld area, or weld area. form of micropoints or microspheres can be

used.

  According to the invention, the elementary amount of heat used during the welding operation is carefully controlled. This elementary quantity depends on the effective mass of the tool, the temperature of the tool, the energy supplied during the welding , as well as the mass of the wire and the copper foil forming the

  connection range on the circuit board.

  The temperature of the welding tip is also

  so that the temperature profile has a desired shape such that the greatest amount of heat is available for the formation of the weld so that the heat

  migrates to platelet regions that are sensi-

heat is minimal.

  The conditions are chosen so that they

  a quick weld because, when building a circuit board wiring point by point, the output over time can be very important for the

  realization of an efficient cabling machine.

  The conditions chosen must allow the

  like to make good welds regardless of

  the structure placed around the plate.

  rations using circuit boards, the size of the ranges may vary and, in some cases,

  in many cases, large mass

  aunts are associated or placed nearby.

  of the copper surface included in the region of

  affects the heat dissipation and migration.

  According to the invention, the conditions are chosen so that they allow the formation of a good weld within a wide range of conditions normally presented by a circuit board. A series of empirical tests is carried out using welding tools. of different dimensions and by different excitation of these tools with different amounts of energy and during

  different periods so that the proper play of conditions

  The results of these tests

in the following table.

BOARD

  Effective Mass Volume 2 (mmx: 10) 8.4 9.4, 9 11.7 12.5 28.0 Tool Size (mm) 0.55 x 0.30 x 0.50 0.50 x 0.38 x 0.50 0.55 x 0, 40 x 0.50 0.55 x 0.43 x 0.50 0.50 x 0.50 x 0.50 0.76 x 0.76 x 0 , 50 Continuous voltage V 4.25 6.40 8.60 4.40 8, 60 4.20

6 ', 50

  8.60 4.20 6.50 8.60 4.40 6.60 8.60 4.15 6.50 8.30 Training Intensity Time

continues a good

  A soldering of a strip of 0.76 mm width ms 250 * * 330 * 425 *

11 14

6 8

Training time

a good

  welding of a 25.4 mm wide band

12 23

6 8

60 110 -

22 24 30 -

12 15

17 18

-

Recou-

  time wise ms 12-14 6 8 T o-tool tool oc **

1100-1200

580-1200

1000-1300

700-1000

840-1145

760-1200 o

400-1200

580-1100

1100-1200

400-1200

800-1200

23 1040-1300

580-1100

  * Approximate values calculated.

  ** Visual estimate based on color temperature.

fi> n

  The dimensions of the tool represent the

  The height and length (W x H x L) of the effective weld mass as shown in Fig. 3 for example, the dimensions of the first row of the table indicate a width of 0.56 mm, a height of 0 , 3 mm and a length of 0.5 mm for a total volume of the mass -2 effective which is 8.4 10 mm 2 The-voltage applied to the tool is 4.25 V, so that the current intensity

is 175 amperes.

  Tests are conducted to study the operation in a wide range of conditions that may be encountered in industrial operations

  printed circuit board processing, by using

  standard platelet configurations using a relatively small area of connection area, in the form of a 0.76 mm strip, and with a relatively large area of connection area, in the form of a strip; 25.4 mm wide The tests carried out on these strips represent a ratio of approximately 30/1 for the width

  so that they simulate the wide range of conditions

  countered in an industrial operation Tests are then performed with different welding times for

  the various conditions, then by inspection and determination

visualization of welds.

  Conditions that give acceptable welds

  tables are shown in the table For example, as

  indicates the second line of the table, a tool for

  having an effective mass with a volume of -2

  8.4 10 mm 3 is powered by a voltage of 6.4 V and gives

  a current intensity of 250 A in the tool On the relatively narrow band (width of 0.75 mm), a

  suitable welding is carried out with periods of exci-

  between 11 and 14 milliseconds when

  these periods are shorter (less than 11 milli-

  seconds in this case), the amount of heat is not sufficient to remove the insulation or to form a

  good welding longer excitation times (de-

  passing 14 milliseconds in this case) cause a

  deterioration of the substrate or wire insulation outside the weld region Tests conducted with a wider band (25.4 mm wide) show that suitable welds are formed for a period of exci-

  between 12 and 23 milliseconds.

  12 and 14 milliseconds, the use of a tool having

  These particular dimensions allow for the formation of

  suitable lengths irrespective of the size of the connection ranges, ie in the range of 0.75

at 25.4 mm.

  The temperature of the tool is determined visually

  The second line of the table indicates that the tool temperature is estimated at 1000 ° C, according to the color red.

clear cherry.

  This series of experiments shows that there is

  conditions which can be chosen for the realization

  Satisfactory welds in a range of conditions encountered in normal industrial operations As indicated in lines 2 and 3 of Table 1, when the mass of the welding tool is relatively small (corresponding to a volume of the effective mass of 8.4 10-2 mm 3, the tool being excited with a potential of 6.4 or 8.6 V, the intensity of the current being 250 or 275 A) 7, there are periods of excitation which give

  satisfaction throughout the entire range of conditions of

  For the lower potential of 6.4 V (corresponds to

  at a current of 250 A), an excitation period of 12 to 14 milliseconds gives a temperature of the end of 10000 C and allows the realization of suitable welds

  throughout the range of dimensions of the connection areas.

  Similarly, for the relatively high potential of 8.6 V (corresponding to a current intensity of 275 Aj, an excitation period of between 6 and 8 milliseconds, at a corresponding tool temperature of 1100 to 12000 C gives also suitable welds throughout the range

  dimensions of the connection areas.

* As also indicated in the table, if the range of dimensions of the beaches is narrower or if all the beaches have the same dimension, one can find other conditions which give satisfactory welds.

  It should be noted that, in all cases, the excitement period

  is less than 500 milliseconds and thus allows

  fast welding useful in automatic machines.

  In most cases, satisfactory welds are obtained with excitation periods of less than 150 ms and, in many cases, less than 50 ms. Although, in some cases, suitable welds are formed

  at low temperatures of the welding tool, the temperature

  The tool gap should generally be greater than 530 ° C and preferably between 870 and 11000 ° C. Lower tool temperatures require longer welding times and longer excitation periods and result in greater migration. heat in the wafer substrate Higher temperatures generally give a steeper temperature gradient, with less heat migration and shorter excitation periods with shorter contact times However, temperatures exceeding 11000 C are undesirable because of the faster deterioration

  of the welding tool at these temperatures.

  A tool having dimensions of 0.55 x 0.4 x 0.5 mm (10.9102 mm of volume) supplied at a voltage of 6.5 V (current of 250 A) gives a welding temperature of 760 ° C An excitation period of 22 ms allows the formation of a suitable weld on a range having

a diameter of 1.77 mm.

  The welding tool starts by vaporizing the insulation

  The non-vaporised insulation, outside the welding zone, reaches a maximum temperature of about 3700 C. The copper wire reaches a higher temperature

  at 4000 ° C., about 480 ° C., that is to say about 2600 ° C.

  below the peak temperature of the tool.

  hard reaches a temperature exceeding the temperature of

  merging of 2300 C and normally about 2750 C, corresponding to

  laying at a difference of about 190 ° C with respect to the temperature of the wire, below this temperature. The temperature of the connection range is close to that of the weld. The temperature of the range can normally be

  reach a peak value of about 2600 C, at 150 C

  viron below the welding temperature, and she

  keep a safety value below 2900 C

  the plastic plate of the circuit board reaches normal

  a maximum temperature of approximately 250 ° C, ie about 100 ° C below the temperature of the beach, and remains

  therefore, in conditions of safety inferior to the

  2900 C for which the substrate undergoes a d 4 t -

  most of the weld contained in the hollow part of the beach remains below a

  temperature of about 1750 C and therefore below

  melting point of the weld which is 2300 C. The temperature profile is important because it

  gives the high temperatures and the desired amount of energy

  The heat required for stripping and welding without the amount of heat in the hollow part of the range or circuit board that could be deteriorated is excessive. Higher tool temperatures (and shorter periods of time) excitation) tend to form steeper gradients of temperature and

  As a result, more heat is available.

  nible in the welding area, with no noticeable increase in temperature in regions that could be

  The selection of conditions such as the quantity of

  The elementary heat content provided is only slightly

  that which is necessary for the formation of an effective weld is of very great importance since the heat is consumed by the formation of the weld and does not migrate.

  not in areas that could be damaged.

  During operation, when the heated welding tool first comes into contact with the insulated wire, the

  heat loss is relatively low after rup-

  the insulation, the welding tool comes into contact

  copper wire and the thermal resistance drops

  At this point, the wire that is in contact with

  the tool is heated so that the insulation part

  caught between the wire and the beach can be chased away.

  their remaining after the removal of the insulation must suffice

  for the weld to melt and form the weld connection.

  Temperatures above 370 ° C are required at

  removal of the insulation, while higher temperatures

  2300 C are required for the merger of the

  tough. The energy supplied to the tool must be in the form of a direct current or a high frequency alternating current and must be in the form of pulses of intensity

  when a single pulse is used for the operation

  welding current, the current must have an intensity between 50 and 500 A with a duration of pulses

  between 500 and 5 milliseconds.

  As stated earlier, the two main

  parameters which are regulated according to the invention are the temperature

  tool temperature and the amount of heat supplied Generally, the tool temperature should be as high as possible while being below the temperature which causes significant damage to the tool. The basic amount of heat supplied

  in the welding region, which is a function of the temperature

  ture of the tool, the effective mass of the tool and the excitation period, should only slightly exceed

  the amount of heat needed to remove the insulation

  These conditions can be achieved by producing the welding tool in such a way that it has a certain mass and by adjusting the intensity of the current and the excitation of the tool during a certain period of time. predetermined period, when the tool is in contact

  of the welding wire The proper setting of the quantity

  supplied heat can also be obtained by preheating a predetermined tool so that it

  the appropriate amount of heat, then by putting the

  in contact with the welding region.

  A suitable setting may be obtained by combining previously stored heat and energy supplied during

the contact.

  Preferably, the welding tool exerts a

  pressure to hold the wire in contact with the sur-

  facing the beach and remains in contact until solidification

  In this way, the risk of movement of the wire during solidification is minimized when the elemental amount of heat

  which is necessary is stored beforehand in the

  In this case, the contact period is chosen so that it ensures the transfer of heat, while including a suitable cooling period. When the energy is supplied

  during contact, this period, after the end of the exci-

  tation, is regulated so that a suitable period of cooling

  Preferably, the tool is real-

  so that, after the proper elemental amount of heat has been supplied to the weld, the tool, while remaining in contact, dissipates heat from the weld. This characteristic can be obtained for example by arm arrangement 36 and 37 support

  (Figure 3) heat conductors and in thermal contact

than with the mass 32 of the tool.

  In some cases, a multiple excitation

  For example, a first pulse can be transmitted for the removal of the insulator and a second separate pulse can then be transmitted for welding. A suitable programmed sequence of two pulses can comprise a first pulse at 6 V

  for 8 ms, removing the insulation, then a second pulse

  This arrangement allows the temperature for stripping (greater than 3700 C) to be present for a short period of time, and a lower temperature (above 2300 C) is then present for a period of time. longer period for welding. As indicated above with reference to FIG. 1, the control apparatus of the tool generally comprises a power supply, a switching circuit

  and a timer control A particular device advancing

  suitable for one-shot welding operations

  pulse is schematically shown in FIG.

  As shown in the table, short and high intensity pulses between 150 and 400 A are

  necessary Although any source may be used

  high current, a battery of accumula-

  70 up to four "Gates BC" accumulators is a suitable source of low voltage, high current. Each accumulator has a nominal voltage

  2 V and a nominal capacity of 25 A h.

  72 charge is mounted across the battery

  to ensure that it is maintained at its maximum

male.

  The switching circuit comprises six switching power NPN transistors 100 to 105, three control NPN transistors 92 to 947 and an initial transistor 90 which is also of the NPN type. The timer control comprises an adjustable monostable multivibrator 82 and a rocker.

associate 80.

  In the figure, a switch 78 is shown

  for triggering the excitation cycle In an apparatus

  real, the switch 78 can be constituted by the

  relay contacts of a computer control

  normally closed tact of the switch 78 is connected to the

  the reset 80 of the flip-flop 80 and the normally open contact at the entry S of establishment one

  outputs of the rocker 80 is connected to the trigger input

  One variable resistor 83 and one capacitor 84 are connected between the + 12 V supply and the monostable circuit 82 so that they give

  the duration setting The capacitor and the resistance

  have the values chosen so that the time intervals can be between 5 and 500 ms. Each time the switch 78 takes the position different from that shown in FIG. 6, the rocker switches state and gives a transistor change. at its output The monostable circuit 82 responds to this transient variation by creating a positive pulse at its output, with a duration that is determined by the setting of the

variable resistance 83.

  The signal from circuit 82 reaches the base of the

  transistor 90 The collector thereof is connected to the

  at + 12 V by a resistor 89 and its emitter is connected to the ground A bias resistor 83 is mounted between the base of the transistor 90 and the power supply

at + 12 V.

  The collector of the transistor 90 is connected to the bases of the control transistors 92 to 94 and to the ground by a resistor 91. The collectors of the transistors 92 to 94 are connected to the positive terminal of the battery via variable resistors 96 to 98. respectively The emitter of the transistor 92 is connected to the bases of the power transistors 100 and 101, the emitter of the transistor 93 is connected to the bases of the transistors 102 and 103 and the emitter of the transistor 94 is connected to the bases

  transistors 104 and 105 The positive terminal of the battery

  70 is connected to a branch 36 of the welding tool 30 and the other branch 37 is connected to the common connection of the collectors of the transistors 100 to 105. The emitters of the transistors 100 to 105 are connected to the negative terminal of the battery. 70 via fuses 110 to respectively The resistors 96 to 98 are used for balancing the circuits of the driving and power transistors so that the load is suitably

distributed.

  A positive impulse transmitted to the output

  of the monostable circuit 82 causes the conduction of the

  1-9 sistor 90 so that transistors 92 to 94 lead and in turn cause the conduction of transistors

  at 105 of power When the transistors of

  the current flows from the posi-

  the battery 70 in the tool 30 and then in the parallel paths of the collector-emitter circuits of the

  transistors 100 to 105 before returning to the nega-

the battery 70.

  Thus, the control of the switch 78 makes it

  generate a high intensity pulse in the tool 30

  with a duration that depends on the setting of the resistance

  83 The intensity of the current flowing through the tool

  depends on the size and composition of it.

  Two accumulators of the battery 70 give a voltage slightly greater than 4 V and, for the dimensions indicated for the tools in Table 1, the pulses formed have

  intensity between 160 and 250 A When using

  three accumulators, the potential is a little

  greater than 6 V and the pulse intensities are

  between 250 and 325 A In the case of the four accumula-

  the potential is greater than 8 V and the pulses have an intensity of between 275 and 425 A. As indicated previously, in some cases

  a sequence of several pulses is preferable,

  taking for example a pulse formed at 6 V for 8 ms for the removal of the insulator at high temperature, then a pulse at 4 V for 25 ms for the formation

  a circuit suitable for such a

  In this case, the energy for the tool comes from a battery with three accumulators comprising two accumulators 121 connected in series with another accumulator 120. battery terminals so

  that it keeps it at its maximum load.

  Two power transistors 180 and 181 placed in parallel connect the source to 4 V to the tool 30 and the

  transistors 170 and 172 form the control circuit cor-

  Three transistors 160 to 162 of global power

  Parallel units are intended to connect the 6 V source to the tool and transistors 150 and 1152 form the associated control circuit. A monostable rocker 130 forms a timer A for adjusting the excitation period. 6 V and a monostable multivibrator 140 forms a timer B for adjusting the excitation period

at 4 V.

  Monostable circuits 130 and 140 have

  variable sistances 131 and 141 respectively mounted between

  the circuit and a source at + 12V Resistors vary

  and the associated capacitors 132 and 142 form the

  timing circuits of monostable multivibrators.

  An input terminal is connected to the trigger input

  130 and the output thereof is connected to the tripping input of the circuit 140. When the resistors 131 and 141 are set for

  8 ms and 25 ms respectively, a temporary signal of de-

  triggering transmitted to terminal 135 causes the transmission

  8 ms positive pulse at the output of the cir-

  cooked 130 then a positive pulse of 25 ms at the output

of circuit 140.

  The output of the circuit 130 is connected to the base of the NPN transistor 150 by a resistor 153. The collector of the transistor 151 is connected to the source at + 12 V by a

  resistance 154 and the base of the NPN transistor 151

  reader of the latter is connected to the source at + 12V per

  series 155 and 156 resistors and the connection of the

  sistances is connected to the base of the NPN transistor 152 The emitters of the transistors 150 and 151 are connected to the ground

  while the emitter of transistor 152 is connected to the source

  at + 12 V The collector of transistor 152 is connected to the bases of power transistors NPN 160 to 162 The positive terminal of battery 120 is connected to the common collector circuit of transistors 160 and 162 mounted in

  whose transmitters return to the negative terminal

  the battery via the fuses 163

at 165 and the welding tool 30.

  The signal of the circuit 140 reaches the mass

  through the resistors 173 and 174 and the

  connection of the resistors is connected to the base of the transistor NPN 170 The emitter of the transistor 170 is connected to the base

  of the NPN transistor 171 and its emitter is connected to ground.

  The collectors of transistors 170 and 171 are connected to the + 12 V source by 175 series transistors and

  176 and the connection of the resistors is connected to the transis-

  tor NPN 172 The transmitter of the latter is connected to the source

  at + 12 V and its collector is connected to the basics of

  Power sistors NPN 180 and 181 The positive terminal

  of the battery 121 is connected to the collector circuit

  parallel transistors 180 and 181 and their transmitters

  are connected to the negative terminal of the battery via fuses 182 and 183 respectively

and the welding tool.

  A trip pulse transmitted to terminal 135 causes formation by the monostable circuit

  130 of an impulse which puts the tran-

  sistors 150 to 152 of the control circuit and these

  then void the conductive state of the parallel transistors of power 160 to 162 Consequently, a

  high intensity impulse, the duration of which is

  undermined by the setting of the variable resistance

  comes to the welding tool 30, from the source

  voltage of 6 V formed by the batteries 120/121

  interruption of the pulse at the output of the circuit 130 pro-

  the operation of the monostable circuit 140 which then creates a pulse which sets the driving transistors to 172 in the conductive state, these in turn putting the parallel power transistors 180 and 181 in the conductive state. high intensity pulse

  reaches the welding tool through the

  32 sistors 180 and 181, from the voltage source of 4 V 121 for a period determined by the setting

variable resistance 141.

  It should be noted that, in the examples described above, the contact force with which the tool holds the wire in contact with the connection pad is advantageously between 1 and 8 N. It is understood that the invention It has been described and represented only as a preferential example and any technical equivalence can be added to its constituent elements without departing from its scope.

Claims (18)

  A method of high speed welding of a wire to a connection pad (60) or the like on a circuit board (5) in the presence of welds, using a welding tool (30) having a predetermined mass, by placing the tool in thermal contact with the wire (11) to be welded and the connection pad (60) and, during the contact, by transmitting to the wire and the connection pad the amount of heat just necessary for the formation of a weld, including the solidification of the weld, characterized in that the effective mass of the welding tool (30) is chosen so that the elementary quantity of thermal energy stored in the weld   this tool only slightly exceeds that which is required   to the formation of an effective weld, this quantity   of heat being practically consumed during the training   the method comprises heating the effective mass to a predetermined temperature so that the weld is formed in less than 500 milliseconds, but the predetermined temperature is less than that which could cause rapid deterioration of the tool (30). ), the elementary quantity of heat being   insufficient for it to migrate significantly into the   circuit board beyond the connection pad (60).   The process according to claim 1 for   welding a wire (11) over a range of   soldered circuit board (60) of a circuit board, the wire being insulated, characterized in that the effective mass of the welding tool (30) is chosen so that the elementary amount of heat stored in the tool when heated to a predetermined elevated temperature   only slightly exceeds the amount of heat required   to vaporize the insulation of the wire (11) and to form an effective weld between the wire (11) and the beach (60).   3. Method according to one of claims 1 and 2,   characterized in that the total contact time is less than less than 50 milliseconds.   4 Process according to claim 1, characterized   in that the welding tool (30) is heated to a temperature of exceeding 530 'C.   Process according to claim 4, characterized in that the welding tool (30) is heated to a temperature of   between 870 and 1100 ° C.   Process according to Claim 1, characterized   in that the welding tool <30) is heated to a temperature of   predetermined high ture before contact with the wire <11) welding.   Method according to one of claims 1 and 2,   characterized in that the welding tool (30-) is heated   at the predetermined elevated temperature after setting tact with the wire (11) to be welded.   Process according to any one of the claims   1 to 7, characterized in that the connection pads (60) are coated with solder before being brought into contact with the welding tool (30).   Method according to claim 8, characterized in that the connection pads (60) are coated with welding to a non-eutectic state.   Method according to one of claims 8 and 9,   characterized in that the connection pads (60) are previously tinned.   11 Process according to any one of 1 to 8, characterized in that the wire (11) coated with solder, before contact with ( 30).   Process according to any one of 1 to 11, characterized in that the material for forming the weld is in the form. Process according to any one of 1 to 11, characterized in that the material for the formation of the weld is of a paste. demands   is the welding tool demands solder used form of a demands   solder used fluid form or   Process according to any one of the claims   14. 1 to 13, characterized in that the welding tool (30) remains   in contact with the wire (11) until solidification of the weld.   Process according to any one of the claims   to 14, characterized in that the volume of the effective mass   cace of the welding tool (30) is of the order of 8 10 2 mm 3.   Process according to any one of the claims   1 to 15, characterized in that the welding tool (30) is -   heated to the predetermined temperature by circulation of an electric current having an intensity of between   50 and 500 A, for a period between 5 and 100 ms.   Method according to one of claims 1 and 2,   characterized in that the welding tool (30) keeps the wire (11) in contact with the connection pad (60) with a contact force of between 1 and 8 N.   Process according to any one of the claims   1 to 17, characterized in that the welding tool (30) is heated to give the following temperature profile   a) a welding tool temperature (30) greater than   less than 540 ° C, (b) a wire insulator vaporization temperature (11) greater than 4000 C,   (c) a temperature in the range of   wherein the solder melts at a temperature greater than 2300 C, and a temperature at the substrate (5) near the connection pad (60) is less than 2900 C.   Method according to one of claims 1 and 2,   characterized in that the small effective mass of the welding tool (30) is thermally coupled to a larger mass so that heat is dissipated into the larger mass and cools the solder material when the weld has been executed.