FR2475960A1 - Joining workpieces by solder preforms without using flux - where preform is shielded from oxidn. by thin coating of non:corrodible metal such as gold - Google Patents

Joining workpieces by solder preforms without using flux - where preform is shielded from oxidn. by thin coating of non:corrodible metal such as gold Download PDF

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Publication number
FR2475960A1
FR2475960A1 FR8003412A FR8003412A FR2475960A1 FR 2475960 A1 FR2475960 A1 FR 2475960A1 FR 8003412 A FR8003412 A FR 8003412A FR 8003412 A FR8003412 A FR 8003412A FR 2475960 A1 FR2475960 A1 FR 2475960A1
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Prior art keywords
preform
welding
metal
gold
flux
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Granted
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FR8003412A
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FR2475960B1 (en
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Christian Val
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Thales SA
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Thomson CSF SA
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Publication of FR2475960B1 publication Critical patent/FR2475960B1/fr
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    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
    • H01L21/50—Assembly of semiconductor devices using processes or apparatus not provided for in a single one of the subgroups H01L21/06 - H01L21/326, e.g. sealing of a cap to a base of a container
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    • H01L23/053—Containers; Seals characterised by the shape of the container or parts, e.g. caps, walls the container being a hollow construction and having an insulating or insulated base as a mounting for the semiconductor body
    • H01L23/057—Containers; Seals characterised by the shape of the container or parts, e.g. caps, walls the container being a hollow construction and having an insulating or insulated base as a mounting for the semiconductor body the leads being parallel to the base
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/30—Assembling printed circuits with electric components, e.g. with resistor
    • H05K3/32—Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits
    • H05K3/34—Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits by soldering
    • H05K3/3457—Solder materials or compositions; Methods of application thereof
    • H05K3/3478—Applying solder preforms; Transferring prefabricated solder patterns

Abstract

The preform is made of a metal cpd. with a low m.pt., and which is oxidisable, so the preform is coated with a metal which neither oxidises nor corrodes at the soldering temp. The metal coating is pref. a pure metal or a eutectic, and is applied by chemical- or electrol- plating, or by vacuum vapour deposition. The preform is used esp. for the assembly of microelectronic components and, in an example, the preform is coated with a thin layer of gold. Used esp. in mfg. micro-packages or chip carriers without using fluxes, which are very difficult to remove after soldering and can impair the quality of the prods.

Description

L'invention concerne un procédé d'assemblage de pièces utilisées en électronique. Elle s'applique plus particulièrement au procédé de soudure pour la fermeture de micro-boitiers et plus généralement à la liaison d'éléments par soudure à base de métaux oxydables. Cependant, elle permet de travailler avec des alliages ou des eutectiques à base de métaux oxydables, sans avoir recours à des flux ou au procédé de soudure sous gaz neutre ou réducteur. The invention relates to a method of assembling parts used in electronics. It applies more particularly to the welding process for closing micro-boxes and more generally to the bonding of elements by welding based on oxidizable metals. However, it makes it possible to work with alloys or eutectics based on oxidizable metals, without resorting to fluxes or to the welding process under neutral or reducing gas.

L'invention sera décrite en s'appuyant sur un exemple de réalisation dans lequel le micro-boitier est un chip carrier", c'est-à-dire un boîtier pour pastille de dispositif semi-conducteur > mais exemple choisi pour exposer l'invention ne restreint nullement le champ d'application de l'invention qui couvre toutes les soudures délicates en électronique, telles que soudure de pastille active ou de composant passif sur un support, soudure de fils de connexion sur les poteaux de boîtiers et les préformes de soudure en général. The invention will be described on the basis of an exemplary embodiment in which the micro-housing is a chip carrier ", that is to say a housing for a chip of semiconductor device> but example chosen to expose the invention in no way restricts the scope of the invention which covers all delicate soldering in electronics, such as soldering of active patch or of passive component on a support, soldering of connection wires on the poles of housings and the preforms of welding in general.

La technique de soudure dite "tendre" s'applique en particulier à la fixation des pastilles de semiconducteur actif sur des embases, et à la fermeture des boîtiers : il faut donc dans la suite de ce texte exclure tout rattachement aux soudures par ultrasons ou par thermo-compression, avec écrasement de fil ou écrasement de-boule, qui sont en dehors du domaine de l'invention. Les Eoudures concernées par l'invention sont celles dans lesquelles est rapporté un alliage ou eutectique à bas point de fusion, tels que par exemple les alliages plomb-étain à 37 - 63 % en poids, ou or-étain à 80 - 20 % en poids
Selon les techniques de soudure connues, la fusion-d'un métal ou d'un alliage, oxydable par l'air ou corrod ble par différents agents gazeux qui peuvent zetre créés au cours de la soudure, tels que sulfures, nitrures ou halogênures, nécessite soit de détruire -cas composes formés et#c'est l'action des flux, soit d'empêcher leur formation et c'est ce qui est fait lors de soudures-sous atmosphères neutre ou réductrice.The so-called "soft" soldering technique applies in particular to the fixing of the active semiconductor wafers on bases, and to the closure of the housings: it is therefore necessary in the following of this text to exclude any attachment to the ultrasonic or thermo-compression, with wire crushing or ball crushing, which are outside the scope of the invention. The Eoudures concerned by the invention are those in which an alloy or eutectic with low melting point is reported, such as for example lead-tin alloys at 37 - 63% by weight, or gold-tin at 80 - 20% by weight
According to known welding techniques, the fusion of a metal or an alloy, oxidizable by air or corrodible by various gaseous agents which can be created during welding, such as sulphides, nitrides or halides, requires either to destroy -compounds formed and # this is the action of fluxes, or to prevent their formation and this is what is done during welds-in neutral or reducing atmospheres.

Les flux sont des composés liquides à température ambiante, qui ont pour -fonction d'empêcher la formation de composés néfastes à la qualité de la soudure. Fluxes are compounds which are liquid at room temperature, which have the function of preventing the formation of compounds harmful to the quality of the weld.

Les flux sont très difficiles à enlever complètement après l'opération de soudure. La soudure sous atmosphère réductrice n'est pas toujours compatible avec les composants manipulés : c'est le cas par exemple des condensateurs multi-couches à armature en palla dium qui ne peuvent pas titre soudés en présence daune atmosphère contenant de l'hydrogène.Fluxes are very difficult to remove completely after the welding operation. Welding in a reducing atmosphere is not always compatible with the components handled: this is the case, for example, of multi-layer capacitors with palladium frame which cannot be welded in the presence of an atmosphere containing hydrogen.

La po ésente invention concerne une nouvelle solution consistant à éviter que le métal ou l'alliage ne soit au contact de l'atmosphère ambiante, au moins avant et pendant la fusion. The present invention relates to a new solution consisting in preventing the metal or alloy from being in contact with the ambient atmosphere, at least before and during the fusion.

Cet objectif est atteint au moyen d'une protec-tion de ia préforme de soudure par une fine pellicule constituée d'un métal ou d'un alliage non oxydable et non corrodable, et ne conduisant pas à la formation de composés inter-métalliques#rragilisants. Ainsi, selon l'invention, la soudure constitue-l'un des composants à assembler et elle se présente comme un objet en préforme, c'est-à-dire un objet découpé selon la forme définitive de l'assemblage.  This objective is achieved by means of a protection of the welding preform by a thin film made of a metal or of a non-oxidizable and non-corrodible alloy, and not leading to the formation of inter-metallic compounds # irritants. Thus, according to the invention, the weld constitutes one of the components to be assembled and it appears as a preform object, that is to say an object cut according to the final shape of the assembly.

De façon plus précise, l'invention consiste en un procédé d'assemblage de pièces par soudure sans flux, dans lequel les pièces sont soudées entre elles au moyen d'une préforme d'un composé métallique à bas point de fusion et oxydable, caractérisé en ce que la surface de la préforme est protégée contre l'oxydation au moyen d'une pellicule métallique non oxydable et non corrodable à la température de fusion de la préforme. More specifically, the invention consists of a method of assembling parts by fluxless welding, in which the parts are welded together by means of a preform of a metallic compound with a low melting and oxidizable point, characterized in that the surface of the preform is protected against oxidation by means of a non-oxidizable metallic film which is not corrodable at the melting point of the preform.

L'invention sera mieux comprise au moyen de la description, laquelle s!appuie sur des figures d'un exemple de réalisation, qui représentent
- figure 1, une préforme de soudure ;
- figure 2, un boîtier d'encapsulation#, vu en coupe, montrant le procédé d'asseg
- figure 3, un détail agrandi de la figure 2 montrant la protection de la préforme pendant la phase de fusion.The invention will be better understood by means of the description, which is based on figures of an exemplary embodiment, which represent
- Figure 1, a weld preform;
- Figure 2, an encapsulation box #, seen in section, showing the asseg
- Figure 3, an enlarged detail of Figure 2 showing the protection of the preform during the melting phase.

La figure 1 représente une préforme telle qututi- lisée pour la soudure des-micro-boitiers appelés "chip carrier
Ces micro-boitiers sont des boîtiers de forme généralement carrée ou rectangulaire, utilisés entre autre dans le domaine des circuits hybrides pour manipuler et tester les pastilles de semi-conducteurs. Ils sont constitués d'une embase sur laquelle sont soudées la pastille semi-conductrice et une grille de connexion ; il est nécessaire de rapporter sur le tout un couvercle de protection mécanique soudé au moyen d'une préforme de soudure. C'est pourquoi la préforme représentée figure 1 a une forme carrée, évidée en son centre.FIG. 1 represents a preform as used for the welding of micro-boxes called "chip carrier"
These micro-boxes are boxes of generally square or rectangular shape, used inter alia in the field of hybrid circuits for handling and testing the semiconductor wafers. They consist of a base on which the semiconductor chip and a connection grid are welded; it is necessary to add on the whole a mechanical protection cover welded by means of a welding preform. This is why the preform shown in FIG. 1 has a square shape, hollowed out at its center.

Il existe d'autres préformes, pleines, ou rondes selon l'usage qui doit en être fait, par exemple souder la pastille semi-conductrice sur l'embase. L'intérêt de cette figure 1 est de montrer, grâce à un écorché dans un coin du dessin, que l'Ame de l'objet est constituée par un ruban de-soudure 1 à proprement parler ; cette soudure peut être par exemple, comme-il -l'à déjà été dit, un alliage plomb-étain à 37 - 63 ss en poids ou un alliage or-étain à 80 - 20 % en poids.There are other preforms, full or round depending on the use to be made of it, for example soldering the semiconductor chip on the base. The interest of this figure 1 is to show, thanks to a cut-away in a corner of the drawing, that the Soul of the object is constituted by a welding tape 1 strictly speaking; this solder can be for example, as it has already been said, a lead-tin alloy at 37 - 63 ss by weight or a gold-tin alloy at 80 - 20% by weight.

Sur cette âme 1 est déposée par voie chimique, -électro- chimique, ou par pulvérisation sous vide, une couche d'un métal non oxydable, tel que de l'or par exemple, d'épaisseur inférieure à 1 micron. C!est cette couche 2 qui forme une "peau" de protection à la surface de la préforme de soudure.On this core 1 is deposited by chemical, -electrochemical, or by vacuum spraying, a layer of a non-oxidizable metal, such as gold for example, of thickness less than 1 micron. It is this layer 2 which forms a protective "skin" on the surface of the welding preform.

Le rapport des masses entre le métal non oxydable et le métal ou l'alliage de soudure est faible et ne modifie pas d'une façon générale la température de fusion, ou plus-précisément la température du liquidus et du solidus de l'alliage dans des proportions élevées. The mass ratio between the non-oxidizable metal and the metal or the solder alloy is low and does not generally modify the melting temperature, or more precisely the temperature of the liquidus and the solidus of the alloy in high proportions.

S'il se faisait que la dissolution de la "peau" de métal non oxydable dans le métal ou l'alliage de soudure atteigne des concentrations dangereuses, ou tende vers la formation de composés intermétalliques fragilisants, il suffirait d'appauvrir l'alliage de soudure en l'un de ses constituants, par exemple en or s'il s'agit d'un alliage or-étain.If the dissolution of the "skin" of non-oxidizable metal in the metal or the welding alloy were to reach dangerous concentrations, or tended towards the formation of embrittling intermetallic compounds, it would suffice to deplete the alloy of solder in one of its constituents, for example in gold if it is a gold-tin alloy.

La préforme étant déposée entre les deux pièces à assembler, des qu'elle fond, sa "peau" en métal inoxydable l'emprisonne dans une g#aine qui la protège de toute oxydation en corrosion externe pendant une durée égale à la durée de dissolution dans l'alliage du métal constituant la gaine. Les dimensions et la masse de la préforme, et les forces de tensions superficielles, sont suffisantes pour maintenir la préforme fondue à l'intérieur d'une pellicule homogène qui la protège de l'oxydation. Dans le cas pris à titre d'exemple, une soudure tendre plomb-étain recouverte d'une pellicule d'or, la durée de protection avant dissolution de l'or dans le plomb-étain atteint 10 à 15 sec, c 'est-à-dire un temps nettement suffisant pour effectuer une soudure.Lorsqu'il y a eu dissolu- tion, il convint de refroidir#afin de limiter l'oxydation en phase solide. The preform being deposited between the two parts to be assembled, as soon as it melts, its "skin" in stainless metal traps it in a sheath which protects it from any oxidation in external corrosion for a period equal to the duration of dissolution. in the alloy of the metal constituting the sheath. The dimensions and mass of the preform, and the surface tension forces, are sufficient to keep the molten preform inside a homogeneous film which protects it from oxidation. In the case taken by way of example, a soft lead-tin solder covered with a film of gold, the duration of protection before dissolution of the gold in the lead-tin reaches 10 to 15 sec, that is that is to say a time clearly sufficient to carry out a weld. When there has been dissolution, it is advisable to cool # in order to limit the oxidation in solid phase.

La figure 1 représente une préforme constituée par un objet distinct des autres objets à assembler cependant appartint au domaine de l'invention le cas où l'une des deux pièces à assembler a été localement recouverte de l'alliage de soudure, par trempé par exemple, la soudure étant ensuite elle-même recouverte d'une pellicule protectrice par voie chimique par exemple. FIG. 1 represents a preform constituted by an object distinct from the other objects to be assembled, however, belonged to the field of the invention, the case where one of the two parts to be assembled has been locally covered with the welding alloy, for example by dipping , the weld then being itself covered with a protective film by chemical means for example.

La figure 2 représente un boîtier d'encapsulation du type "chip carrier" vu en coupe et montre le procédé d'assemblage selon l'invention. FIG. 2 represents an encapsulation box of the "chip carrier" type seen in section and shows the assembly method according to the invention.

Un boîtier ttchiF carrier" est essentiellement constitué par une embase 3, généralement en céramique, sur laquelle il faut souder un couvercle 4, en céramique également, par l'intermédiaire d'une préforme 5. A ttchiF carrier "housing essentially consists of a base 3, generally made of ceramic, on which a cover 4, also made of ceramic, must be welded, by means of a preform 5.

La préforme 5 est du type de celle montrée en figure 1 et est recouverte d'une pellicule inoxydable.The preform 5 is of the type shown in FIG. 1 and is covered with a stainless film.

L'embase 3 supporte une pastille semi-conductrice 6, ou un composé passif, relié par des fils de connexion 7 à une grille de sortie ou à des métallisations repliées sous l'embase. Un joint intercalaire 9 est, avant l'opération de fermeture du boîtier, fixés sur le pourtour de l'embase 3 : ce joint intercalaire est en matériau isolant, sa fonction est d'empêcher que la soudure ne court-circuite entre elles les connexions de sortie 8, mais sa face supérieure 10 a été métallisée de façon à permettre une soudure ultérieuse. The base 3 supports a semiconductor patch 6, or a passive compound, connected by connection wires 7 to an outlet grid or to metallizations folded under the base. An intermediate seal 9 is, before the closing operation of the housing, fixed on the periphery of the base 3: this intermediate seal is made of insulating material, its function is to prevent the solder from short-circuiting the connections between them. outlet 8, but its upper face 10 has been metallized so as to allow a subsequent weld.

De la même façon, la partie 11 du couvercle sur laquelle sera effectuée l'opération de soudure a été précédemment métallisée, par exemple par trempage ou par sérigraphie. Le procédé d'assemblage consiste donc à#réunir l'embase 3 et tous les accéssoires qu'elle supporte au eouverele 4 par l'intermédiaire d'une préforme de soudure 5, laquelle est protégée par une pellicule inoxydable selon ltinvention. In the same way, the part 11 of the cover on which the welding operation will be carried out has been previously metallized, for example by dipping or by screen printing. The assembly process therefore consists in # joining the base 3 and all the accessories that it supports to the cover 4 by means of a welding preform 5, which is protected by a stainless film according to the invention.

La figure 3 est un détail agrandi de la figure 2 et montre la partie du couvercle 4 sur laquelle est effectuée l'opération de soudure. La face 11 du couvercle 4 est métallisée de façon à permettre l'adhé- reste de la-s-oudure, chose qui ne serait pas possible si cette mame face il était en céramique.La soudure à proprement parler, c'est-à-direpar exemple un alliage plomb-étain > constitue pendant la phase de fusion un ménisque representé en 12. Sans la précaution prise au titre de l'invention, ce ménisque stoxyderaXt en surface et l'assemblage serait de mauvaise qualité, ou bien alors il faudrait faire intervenir soit un flux, soit une atmosphère réduc- trice, ce que l'on veut éviter La fine pellicule le métal inoxydable 13 constitue une protection contre l'oxydation de la soudure, protection qui dure suffisamment longtemps avant dissolution de ce métal dans la masse de soudure pour que l'opération ait le temps entre achevée. Figure 3 is an enlarged detail of Figure 2 and shows the part of the cover 4 on which the welding operation is carried out. The face 11 of the cover 4 is metallized so as to allow the adhesion of the remainder, something which would not be possible if this same face were made of ceramic. The welding proper, that is to say - say for example a lead-tin alloy> constitutes during the melting phase a meniscus represented at 12. Without the precaution taken under the invention, this meniscus stoxyderaXt on the surface and the assembly would be of poor quality, or else it either a flux or a reducing atmosphere should be brought into play, which is to be avoided. The thin film of the stainless metal 13 constitutes protection against oxidation of the weld, protection which lasts long enough before this metal dissolves in the solder mass so that the operation has the time between completed.

Les applications-de ce procédé d'assemblage concernent en particulier les préformes de soudure plomb-étain rev#tues d'or pour souder sans flux des fils de connexions sur des poteaux de boîtiers métal liques du type semi-conducteur discret, ou ou préformes or-étain telles qu'utilisées pour fermer des boîtiers céramiques du type "chip carrier". Cependant, d'autres applications de soudure entre des éléments utilises en micro-électronique et notamment dans le domaine des circuits hybrides sont possibles et appartiennent au domaine des revendications ci-après.  The applications of this assembly method relate in particular to lead-tin solder preforms coated with gold for soldering without flux the connection wires on metal housing poles of the discrete semiconductor type, or preforms gold-tin as used to close ceramic boxes of the "chip carrier" type. However, other applications of soldering between elements used in microelectronics and in particular in the field of hybrid circuits are possible and belong to the field of claims below.

Claims (9)

REVENDICATIONS 1. Procédé d'assemblage de pièces par soudure, sans flux, dans lequel les pièces sont soudées entre elles par apport d'une préforme d'un composé métallique à bas point de fusion et oxydable, caractérisé en ce que la surface de la préforme est protégée contre l'oxydation au moyen d'une pellicule métallique non oxydable et non corrodable à la température de fusion de la préforme. 1. A method of assembling parts by welding, without flux, in which the parts are welded together by providing a preform of a metallic compound with low melting point and oxidizable, characterized in that the surface of the preform is protected against oxidation by means of a metal film which cannot be oxidized and cannot be corroded at the melting point of the preform. 2. Procédé selon la revendication 1, caractérisé en ce que la pellicule métallique est constituée par un métal pur. 2. Method according to claim 1, characterized in that the metallic film consists of a pure metal. 3. Procédé selon la revendication 1, caractérisé en ce que la pellicule métallique est constituée par un alliage de composition voisine de l'eutectique. 3. Method according to claim 1, characterized in that the metallic film is constituted by an alloy of composition close to the eutectic. 4. Procédé selon la revendication 1, caractérisé en ce que la pellicule métallique est déposée sur la plateforme par voie chimique. 4. Method according to claim 1, characterized in that the metallic film is deposited on the platform by chemical means. 5. Procédé selon la revendication i, caractérisé en ce que la pellicule métallique est déposée sur la préforme par voie électrochimique. 5. Method according to claim i, characterized in that the metallic film is deposited on the preform by electrochemical means. 6. Procédé selon la revendication 1, caractérisé en ce que la pellicule métallique est déposée sur la plateforme par vaporisation sous vide. 6. Method according to claim 1, characterized in that the metal film is deposited on the platform by vacuum spraying. 7. Préforme de soudure à bas point de fusion, caractérisé en ce que sa surface est protégée par une pellicule selon l'une quelconque des revendications 2 à 6. 7. Low melting point welding preform, characterized in that its surface is protected by a film according to any one of claims 2 to 6. 8. Composant micro-électronique, caractérisé en ce que ses constituants sont assemblés par soudure selon l'une quelconque des revendications 1 à 6 du procédé d'assemblage.  8. Microelectronic component, characterized in that its constituents are assembled by welding according to any one of claims 1 to 6 of the assembly process. 9. Composant micro-électronique, caractérisé en ce que ses constituants sont assemblés par soudure au moyen d'une préforme selon la revendication 7.  9. Microelectronic component, characterized in that its constituents are assembled by welding by means of a preform according to claim 7.
FR8003412A 1980-02-15 1980-02-15 Joining workpieces by solder preforms without using flux - where preform is shielded from oxidn. by thin coating of non:corrodible metal such as gold Granted FR2475960A1 (en)

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FR8003412A FR2475960A1 (en) 1980-02-15 1980-02-15 Joining workpieces by solder preforms without using flux - where preform is shielded from oxidn. by thin coating of non:corrodible metal such as gold

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FR8003412A FR2475960A1 (en) 1980-02-15 1980-02-15 Joining workpieces by solder preforms without using flux - where preform is shielded from oxidn. by thin coating of non:corrodible metal such as gold

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8359740B2 (en) 2008-12-19 2013-01-29 3D Plus Process for the wafer-scale fabrication of electronic modules for surface mounting

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB734195A (en) * 1952-05-19 1955-07-27 John Cockbain Briggs Improvements in and relating to solders
US4020987A (en) * 1975-09-22 1977-05-03 Norman Hascoe Solder preform for use in hermetically sealing a container

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB734195A (en) * 1952-05-19 1955-07-27 John Cockbain Briggs Improvements in and relating to solders
US4020987A (en) * 1975-09-22 1977-05-03 Norman Hascoe Solder preform for use in hermetically sealing a container

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8359740B2 (en) 2008-12-19 2013-01-29 3D Plus Process for the wafer-scale fabrication of electronic modules for surface mounting

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