Electronic module produced by sequential fixation of the components

Abstract

A production line for producing electronic modules including a printed-circuit board, at least one first-type component, and at least one second-type component, wherein the production line includes a unit for putting the first-type component in place, a general heating unit for melting a solder placed between the at least one first-type component and the circuit, a unit for putting the second-type component in place, and a local heating unit for melting a solder placed between the at least one second-type component and the circuit.

Claims

1. A production line for producing electronic modules, comprising: a printed-circuit board; at least one first-type component; and at least one second-type component, wherein the line comprises a first placement unit for putting the at least one first-type component in place, a general heating unit for melting a solder placed between the at least one first-type component and the printed-circuit board, a second placement unit for putting the at least one second-type components in place and a local heating unit for melting a solder placed between the at least one second-type component and the printed-circuit board, and wherein the local heating unit comprises a pair of electrodes, wherein each electrode of the pair of electrodes is configured to contact a lead of the second-type component so as to make an electrical current flow between the pair of electrodes via the lead of the second-type component for heating each lead of the component sufficiently in order to melt the solder located between the lead and the printed-circuit board, wherein temperature of the electrodes is kept substantially constant and at approximately a low temperature of 40 C., and wherein a power supply is operatively connected to the pair of electrodes such that the electrical current flows between the electrodes to heat the lead of the second-type component, the electrical current having a current intensity curve as a function of time that comprises a minimum frequency of 1,000 Hz.

2. The line as claimed in claim 1, in which the general heating unit comprises a reflow oven.

3. A production line for producing electronic modules, comprising: a printed-circuit board; at least one first-type component; and at least one second-type component, wherein the line comprises a first placement unit for putting the at least one first-type component in place, a general heating unit for melting a solder placed between the at least one first-type component and the printed-circuit board, a second placement unit for putting the at least one second-type components in place and a local heating unit for melting a solder placed between the at least one second-type component and the printed-circuit board, and wherein the local heating unit comprises a pair of electrodes, wherein each electrode of the pair of electrodes is configured to contact a lead of the second-type component so as to make an electrical current flow between the pair of electrodes via the lead of the second-type component, wherein temperature of the electrodes is kept substantially constant and at approximately a low temperature of 40 C., wherein a power supply is operatively connected to the pair of electrodes such that the electrical current flows between the electrodes to heat the lead of the second-type component sufficiently to melt the solder located between the lead and the printed-circuit board, and wherein each electrode of the pair of electrodes is configured to contact the lead by contacting a flat surface of the lead, the flat surface being opposite to the printed-circuit board.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Reference will be made to the appended drawings, in which:

(2) FIG. 1 is a schematic view of a production line for manufacturing electronic modules according to the invention;

(3) FIG. 2 is a partial schematic view in perspective of such a module during the soldering of a component; and

(4) FIG. 3 is a view similar to that of FIG. 2 of this module after the component has been soldered.

DETAILED DESCRIPTION OF THE INVENTION

(5) Referring to the figures, the manufacturing process according to the invention is implemented on a production line, designated generally as 1, for manufacturing electronic modules generally designated as 2.

(6) An electronic module 2 comprises a board 3 on which a conducting circuit 4 has been formed in order to constitute, in a manner known per se, a printed-circuit board. The board 3 is of the IMS (insulated metal substrate) type. The circuit 4 may be formed from a conductive ink spread by screen printing on the board 3. The circuit may also consist of metal tracks fastened to the board 3.

(7) The module 2 also comprises first-type components 5 and a second-type component 6 having connection leads 7, only one of which is shown in FIGS. 2 and 3. The components 5, such as drive components, are smaller than the component 6, which is for example a power component. The component 6 here lies on top of one of the components 5. The connection leads, or more generally the connection members, of the components 5 and 6 are fixed to the circuit 4 by melted solder 8. The solder 8 here is solder paste consisting of a mixture of tin and lead.

(8) The production line 1 comprises a unit 10 for depositing the solder 8 on the circuit 4 of the boards 3, a unit 20 for putting the components 5 in place, an overall heating unit 30, consisting here of a reflow oven, a unit 40 for putting the component 6 in place and a unit 50 for local heating of the components 6.

(9) The units 10, 20, 30 and 40 are known per se.

(10) The local heating unit 50 comprises pairs of electrodes 51 connected to a power supply 52, which here delivers a current of around 3000 amps at a minimum frequency of 1000 hertz. The electrodes here are made of copper-tungsten (25% copper and 75% tungsten).

(11) The various units are linked together conventionally by a conveyer 60 for transporting the boards 3.

(12) The circuit 4 is already printed on the boards 3 when they enter the production line 1.

(13) In the unit 10, the solder 8 is deposited by screen printing on the connection pads of the circuit 4 for the components 5 and 6.

(14) The components 5 are then placed by the unit 20 on the circuit 4 so that the connection members of the components 5 rest on the solder 8 deposited on the corresponding connection pads of the circuit 3.

(15) The board 3 thus furnished with the components 5 passes into the overall heating unit, i.e. the reflow oven 30 which melts the solder 8 and enables the components 5 to be soldered.

(16) It is possible to carry out a visual check of the soldering of the components 5 upon emerging from the reflow oven 30. Since the component 6 is not on the board when it passes through the reflow oven 30, the mass to be heated during this passage is relatively low. This makes it possible to use lower-capacity ovens or pass more boards simultaneously through the oven.

(17) Next, the board 3 passes through the unit 40 in which the component 6 is put in position on the circuit 4 so that the leads 7 of the component 6 rest on the solder 8 deposited on the corresponding connection pads of the circuit 3.

(18) The components 6 are then soldered by applying a pair of electrodes 51 on each lead 7 of the components 6 so as to make an electrical current flow between said electrodes via the corresponding lead 7 and heat each lead 7 of the component 6 sufficiently to melt the solder 8. It will be noted that the pressure of the electrodes on the part to be soldered ensures that the part to be soldered is properly pressed against the circuit. To give an example, the electrodes may exert a force of 12 daN on the part to be soldered.

(19) Melting the solder by means of the electrodes has the advantage of being extremely rapid (less than one second), whereas passage through a reflow oven lasts about one minute.

(20) It is possible to influence the quality of the solder or to adapt the soldering to the materials or components to be soldered by modifying the soldering profile (and in particular the current intensity curve as a function of time, the mechanical pressure of the electrodes on the leads of the components), the geometry of the electrodes (so as in particular to allow better heat extraction), the force exerted on the part (so as to maintain contact between the electrode and the part and prevent the formation of a spark) and the spacing and positioning of the electrodes on the leads (in particular to modify the path of the current through the leads). The temperature of the electrodes is kept approximately constant and relatively low, around 40 C., so as to maintain the same soldering conditions for all the parts, hence the benefit of providing means for facilitating the removal of heat at the electrodes, such as a suitable geometry.

(21) Of course, the invention is not limited to the embodiment described and embodiment variations may be imparted thereto without departing from the scope of the invention as defined by the claims.

(22) In particular, it is possible to deposit the solder used for soldering the components 6 after the components 5 have been soldered by a screen printing operation. The solder may also be deposited directly on the leads of the components before they are put in place on the circuit.

(23) It is possible to heat the paste of the components differently, for example by applying a soldering iron bit on each lead of the components 6 or of the components 5. The heating unit 50 may be a reflow oven.

(24) The electrodes may be made of various metals, especially copper, tungsten, molybdenum, etc. The electrodes thus may be made of copper-tungsten (25% copper and 75% tungsten) as in the embodiment described or made of copper and comprise a tungsten tip for serving as a point of contact with the part to be soldered.

(25) The parts to be soldered may be made of copper, brass, an alloy or a metal, whether tinned or not. The board may be of the IMS type as described or may be of another type comprising, for example, a glass fabric/epoxy resin circuit such as boards of the FR4 type.

(26) It is possible to use other, lead-free solders, based on tin, based on silver, etc. The solder may also be deposited in the form of a metal strip either on the circuit or on the connection members of the components.

(27) The modules may of course have a structure different from that of the above embodiment, which was presented merely to explain the invention and is in no way limiting. The components 6 put in place after the boards have passed through the reflow oven 30 may be bulky components or components that might be damaged by the heat within the oven. The components 6 may be identical to the components 5 but soldered subsequently, in order to prevent excessively high concentrations of components during the first soldering operation.