MXPA99002365A - Laser soldering procedure applicable to the joining of pins over printed circuit boards - Google Patents

Abstract

The proposed procedure, that of laser soldering or welding, is an auto-energetic process in which the density of the laser beam is obtained because of the concentration of light beams. Said process involves two metals (alike or disimilar) and, previously to the metallurgical union, same must be positioned in front of the laser head with enough accuracy. The metallurgical union is carried out by direct fusion of the metals to join, not being therefore necessary any filler metal.

Description

PR, PINS ON PRINTED CIRCUITS The present application for Patent of Invention consists, as indicated by its / in a "LASER WELDING PROCEDURE APPLICABLE TO THE LINKING OF PINS ON PRINTED CIRCUITS", whose new construction, conformation and design characteristics fulfill the mission for which it has specifically been projected, with maximum safety and efficiency. More specifically, the invention refers to the union of short pins on printed circuits of 400 microns, executing the corresponding metallurgical union by direct fusion of the metals to be joined, by means of the energy generated by a laser beam. In the State of the Art to carry out the joining of two metallic elements wave soldering is usually used, in this process several types of defects are usual, such as missing welds, unwelded components, bridges between adjacent welds, micro-crossings , tnicrobslas, entrepistas adjacent to the printed circuit. These defects can cause electric stems, such as short circuits and short circuits that jeopardize the proper functioning of the system. On the other hand, conventional wave welding requires a manual review (after the process itself), to repair the aforementioned defects. The above defects and the associated consequences are solved by applying laser technology for the micro-welding of the components on the printed circuit. This is so since laser welding consists of a direct fusion of the elements to be joined, with which no filler metal is necessary. On the other hand, the laser welding process itself is such that it does not require any other work of the connections made. Alloys usually. used for wave soldering of components on printed circuit have a series of limitations when they are subjected to mechanical, electrical and / or thermal stress. This is due to the difference between the coefficients of thermal expansion and the different materials that intervene in the welded joint: interconnection elements. { short pin, tongue, socket and others), printed circuit. { copper and substrate) and solder alloy. Thus, when the welded joint is subjected to load and / or temperature cycles, as a consequence of the difference between the coefficients of thermal expansion, the weld is subjected to fatigue or stress (thermomechanical fatigue). Said fatigue, and depending on the severity of the stress conditions, can cause the electrical failure of the union. The consequences that can derive from the thermomechanical fatigue are minimized when the union is made using laser technology. This is so since the connection between the interconnection element (usually copper and alloys) and the copper of the printed circuit is carried out by means of a cobra joint constituted by direct fusion of the materials to be interconnected. This implies having a very homogeneous union, and as a consequence an equality in the coefficients of thermal expansion, which minimizes the effects of thermomechanical fatig. From the environmental point of view, its impact, the advantages of laser technology for the realization of welds is justified by the following factors: - The process of welding by lager does not require the use of fluxes or fluxes for chemical cleaning. surfaces to be welded, (as is the case of welding by conventional means). The laser welding process does not require the use of bearing metal, which eliminates the use of alloys with lead content (as is the case with the conventional wave welding process). The procedure recommended, that of laser welding, is a high energy process in which the density of the laser beam is achieved by the concentration of light waves. This process involves two metals (similar or dissimilar) and, prior to the metallurgical union, must be positioned in front of the laser head with sufficient precision. The metallurgical union is made by direct fusion of the metals to be joined, with which no filler metal is necessary. On the surface of the "parts to be joined, the high concentration of light energy is converted into thermal energy.The fusion of surfaces progresses through the thermal conduction junction joint.To produce the welding, the energy of the beam must be maintained by below the evaporation temperature of the material to be bonded The penetration depends basically on the induced heat and the thickness of the materials The technology used allows the realization of welds with areas minimally affected by heat as well as excellent metallurgical quality. Fusion and coalescence before the appearance of areas substantially affected by the heat put in play All metals reflect lightning in the light Metals such as gold, silver, copper and aluminum present difficulty for laser welding This is why they require intense energy, provided by pulses. of very high peak power or coated with some absorbent material (graphite, nickel and others). The flexibility of the laser for its manipulation makes it ideal for use in automated and robotic processes. On the other hand, the use of optical fiber helps to make a laser system more versatile and flexible. Finally, the laser welding process requires the need for a clean work environment (in order to protect the optics), as well as considerations of health and hygiene. Other details and characteristics of the current application for Patent of Invention, will become apparent during the description that follows, in which reference is made to the drawings that accompany this eeta memory, in which, In a somewhat schematic manner, the preferred details are represented. These details are given by way of example, making reference to a possible case of practical realization, but it is not limited to the details that are exposed there; Therefore, this description should be considered from an illustrative point of view and without limitations of any kind. Next, we will list the various elements numbered in the drawings attached to this report; (10) power source, (11) laser cavity, (12) emitted laser beam, (13) mirror, (14) defocused laser beam, (15) focusing optics, (16) workpiece, (17) system of motion, (18) lens, (19) focused laser beam, (20) welding, (21) short pin, (22) copper crown, (23) drill, (24) substrate, (25) joint, (26) ) printed circuit. Figure ns 1 shows a diagram of the recommended welding process. Figure 2 is a simple diagram of the laser arrangement applied to the welding area.

Figure 3 is a diagram of different types of laser welding. Figure ns 4 shows a short pin diagram (21) -inserted in a printed circuit (26), Figure ns 5 shows different possibilities for realizing the union between a short pin (21) and a printed circuit (26). Figure 6 shows the direction and the firing point of the laser beam (19) on a short pin (21). The method recommended in the present invention uses a welding system as described in figure n «1, in which we can see a power source. { 10.}. which transmits it to a laser cavity (ll), which generates in combination with (10) an emitted laser beam (12) that impinges on a mirror (13) which reflects a deefocalized laser beam (14), which penetrates the through a focusing optics (15) and leaves it directed to a work piece (16), which rests in a movement system (17) provided with multiple axes that allow its movement in the coordinates X, Y, Z, so that the work piece (16) can move in the desired directions that allow to collaborate with the welding system. In the figure nd 2 amplia broad part of figure n 1 1 and can be seen how the optic (15) represented by a specific slow (18) produces a focused laser beam (19) so that it affects a weld (20), said focused beam has a penetration power that is specified in a penetration distance d,. The types of welding that can be carried out using the recommended procedure depend, as can be seen in figure «3 of the different thicknesses of the materials to be welded, see figure p2 3a, of the different metals to be welded, see figure nfi 3b and also from the vicinity of the welded terminals. see figure ng 3c. The recommended procedure finds its _ practical realization, for example in welding by -Laser of a workpiece (16) in this case short pins (21) on printed circuits (25), as outlined in figure nd 4, in which you can see how a short pin (21) goes through a printed circuit (26), formed by a substrate (24) covered on both sides with copper conducting tracks and in the vicinity of (21) of copper crowns (22). Prior to the laser welding operation and according to a conventional solution, a series of holes is provided in the printed circuit (26) to subsequently mechanically insert said pins (21), so that they are arranged as shown in FIG. figure nd 4, then the recommended laser welding melts the material of the pin (21) and the copper crown (22) producing the joints (25). Said joints (25), as shown in Figure 5, "can be made in different situations, either in one of the vertices, of what could be described as a junction, in one of the bases of the pin (21). ), which could be cited as a lateral junction, or in the center of one of these bases that could be called a central union.The direction and firing point of a focused laser beam (19) is shown in figure 6, in which a printed circuit (26) is represented formed by a substrate (24) and copper crowns (22) crossed by a short pin (21) and arranged for the recommended welding, which applies said Focused laser beam (19) with an angle of incidence alpha, which f will oscillate between 30 and 459. The distance "d" indicated in said figure allows to control the amount of material of short pin (21) fused. The melting point of the short pin is greater than that of the crown (22) of the printed circuit (2). 6) to prevent the joint (25) from deteriorating due to changes in temperature. The range of • -variation of said distance "d" is experimentally set between 0 and 0.5 mm. Usually in the recommended laser welding process, a protective gas is used in the environment of the piece to be welded, such as the short pin (21) to avoid oxidation during the welding process itself. The parameters of the laser beam (19) applied, which allow the junction (25) are at a pulse energy between 16 and 40 joules, a peak power between 3,500 to 4,000 years. 5 The numbers of the welding points (25) pair pin (21) can vary between two and four for each face of the pin (21). Logically, the optimal electrical behavior of the system has been found by four welding points for each face of the printed circuit (26). 0 Sufficiently described in what constitutes the patent in correspondence with the attached plans, it is understood that any modifications of detail that may be considered convenient may be introduced, provided that the proposed variations do not alter the essence of the patent that is summarized in the following REINV NDICATIONS.

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Claims (1)

1. R E I V I ND I C AC I O N E S; - "LASER WELDING PROCEDURE APPLICABLE TO LA UNION DE PINES BOBRE CIRCUITOS IMPRESOS "of those who use a high energy process in which the density of the laser beam is achieved by the concentration of light waves and applied to a welding process in which two metals join similar metallurgical natures or not, that prior to their metallurgical union have to be positioned in front of the laser head with due precision, characterized in that said method consists of the arrangement of a power source (10) that is transmitted to a laser cavity (II) ) which generates a laser beam emitted { 12) that falls on a mirror (13), which reflects a defocused laser beam (14), which affects a focusing optics (15), which emits lightning focalized laser (19), on a work piece (16) located on a system (17) of movement in the coordinates X, Y, Z (17), with welding pins, being controlled by the application of metallic coating of the pin (21 ) and inert atmosphere. 28 - "LASER WELDING PROCEDURE APPLICABLE TO THE UNION OF PINS ON PRINTED CIRCUITS" characterized according to the claim 1J in which the welding piece (16) is a short pin (21), arranged on a printed circuit (26), formed by a substrate (24) and copper tracks on both sides of (24) and in the vicinity of the pin (21) copper rings (22) covering a bore (23) produced in the printed circuit (26), prior to insertion of said pin (21) by mechanical methods reaching the simultaneous fusion of the copper ring (22) and one of the faces of the pin (21) producing the junction (25), between (22) 'and (21). 3_ - "LASER WELDING PROCEDURE APPLICABLE TO THE CONNECTION OF PINS ON PRINTED CIRCUITS" characterized according to the 2 »claim in which the connection (25) can be made at the apex of the pin (21). 9 - "LASER WELDING PROCEDURE APPLICABLE TO THE UNION OF PINS ON PRINTED CIRCUITS "characterized according to the 2 * claim that the connection (25) between the pin (21) and the ring (22) can be made in the vicinity of the vertex of the pin (21) .58 -" PROCEDURE OF LASER WELDING APPLICABLE TO THE UNION OF PINS ON PRINTED CIRCUITS "characterized according to the 2 * claim that the union (25) between the pin (21) and the ring (22) can be made in the middle of one of the bases of the short pin (21) . - 68 - "LASER WELDING PROCEDURE APPLICABLE TO THE UNION OF PINS ON PRINTED CIRCUITS "characterized according to the 1 * claim that laser welding can be made between metals of different thicknesses. 7 * - "LASER WELDING PROCEDURE APPLICABLE TO THE UNION OF PINS ON PRINTED CIRCUITS "characterized according to the claim in which laser welding can be made between different metals." 8"- LASER WELDING PROCEDURE APPLICABLE TO THE UNION OF PINS ON PRINTED CIRCUITS "characterized according to the claim in which laser welding can be carried out in the vicinity of welded terminals 9 * -" LASER WELDING PROCEDURE APPLICABLE TO THE LINKING OF PINS ON PRINTED CIRCUITS "characterized according to the ld claim in which, prior to the laser welding operation, a coating such as a nickel layer between 5 and 10 microns will be applied on the surface of the short pin in order to reduce the reflection index IOS - "LASER WELDING PROCEDURE APPLICABLE TO THE UNION OF PINS ON PRINTED CIRCUITS "characterized according to the claim in which the direction and point of firing of the laser beam (19) on the short pin (21) and the copper ring (22) will be an angle comprised between 30 and 350 and the distance "d" will vary between 0 and 0.5 mm lis - "SOLDERING PROCEDURE L BEING APPLICABLE TO THE CONNECTION OF PINS ON PRINTED CIRCUITS" characterized according to the 1 «claim in which in the procedure recommended the atmosphere will be inerted ßl working environment by using protective gases to avoid oxidation during the welding process 12 * - "LASER WELDING PROCEDURE APPLICABLE TO THE UNION OF PINS ON PRINTED CIRCUITS "characterized according to the 1B claim in which a pulse energy, between 16 and 46 joules and a peak power between 3,500 and 4,000 watts will be used." 13 * - "LASER WELDING PROCEDURE APPLICABLE TO THE UNION OF PINS ON PRINTED CIRCUITS "characterized according to the 1st and 3rd claim in which the number of welding points per pin can vary between 2 and 4 points for each face.