FR2840850A1

FR2840850A1 - Support system for printing screen unit, has tensioning mechanism for tensioning printing screen to one tension in printing phase in printing medium onto workpiece and another tension lower than the former one

Info

Publication number: FR2840850A1
Application number: FR0207241A
Authority: FR
Inventors: Francis Bourrieres; Clement Kaiser
Original assignee: Novatec SA
Current assignee: Novatec SA
Priority date: 2002-06-13
Filing date: 2002-06-13
Publication date: 2003-12-19
Anticipated expiration: 2022-06-13
Also published as: FR2840850B1

Abstract

The system has a printing screen (5) with printing apertures (6) through which printing medium is printed onto a workpiece. A mechanism (18) is provided for tensioning the screen to a tension in a printing phase in a printing medium onto the workpiece and another tension, which is lower than the former tension, in a separation phase to separate the printing screen unit and the workpiece. Independent claims are also included for the following: (a) a method of supporting a printing screen unit in a screen printing machine (b) a printing screen unit.

Description

partir de la vis (11).from the screw (11).

PROCEDE DE MISE EN CEWRE D'UN POCHOIR DE SERIGRAPHIE PROCESS FOR FIXING A SCREEN STENCIL

PERMETTANT DE DISSOCIER LE TRAITEMENT DES PHASES DE FOR DISSOCIATING THE TREATMENT OF PHASES OF

REMPLISSAGE ET DE DEMOULAGEFILLING AND DEMOLDING

CHAMP D'APPLICATION DE L'INVENTIONSCOPE OF THE INVENTION

La presente invention trouve son application pour le transfert de produit visqueux a travers un pochoir. Ce type de depot appele serigraphique est particulierement courant dans le domaine de la fabrication electronique ou l'on est amene a deposer des cremes a braser, des colles ou des encres sur un substrat a ['aide d'un pochoir en vue d'y interconnecter des composants ou de creer des bossages 0 d'interconnexion. The present invention finds its application for the transfer of viscous product through a stencil. This type of deposit called screen printing is particularly common in the field of electronic manufacturing where it is necessary to deposit soldering creams, glues or inks on a substrate using a stencil in order to interconnect components or create 0 interconnect bosses.

DESCRIPTION DE L'ART ANTERIEURDESCRIPTION OF THE PRIOR ART

Les pochoirs utilises vent constitues d'une feuille metallique ou plastique pleine, tendue par ses quatre cotes sur un cadre et dans laquelle vent pratiquees des ouverture s aux endro its o u un dep ot do it etre real i se. La s erigraphie consi ste done a apposer le pochoir tendu sur le substrat et a forcer le produit a travers les ouvertures du pochoir a ['aide d'un organe de transfert qui peut etre une racle inclinee ou un dispositif d'injection ferme deplace en appui sur la surface du pochoir, puis le substrat et le pochoir vent separes en vue de ['evacuation du substrat serigraphie et de son remplacement par un autre a traiter. On distingue deux modes de serigraphie au pochoir, le premier qui est aussi le plus utilise, consiste a travailler en contact, ce qui signifie que le pochoir repose sur toute la surface du substrat durant la phase de remplissage des ouvertures puts, lorsque toutes les ouvertures vent remplies, on procede a un demoulage de tous les depots en eloignant le masque tendu selon un mouvement perpendiculaire au substrat. Le deuxieme mode de serigraphie consiste a travailler hors contact, c' est a dire que le pochoir est approche a une distance de quelques dixiemes de millimetres du substrat. Puis lorsque l'organe de transfert est amene en appui sur le pochoir, il pousse le pochoir en contact avec le substrat dans la zone d'appui au fur et a mesure de son deplacement et simultanement il s'opere un mouvement de separation du pochoir et du substrat a l'arriere de l'organe de transfert. Les deux modes de serigraphie presentent un certain nombre d'avantages et d'inconvenients. Le mode hors contact est unanimement utilise pour la serigraphie d'encres liquides a ['aide d'ecrans tisses telle que pratiquee pour ['impression d'affiches ou de tissue. En effet, dans ce cas, il n'est pas fait usage de pochoirs mais d'ecrans constitues d'une maille tissee bouchee aux endroits ne devant pas recevoir d'encre. Les ecrans a maille se present bien a la serigraphie hors contact car leur flexibilite associee a leur elasticite permettent d'obtenir un contact intime entre le masque et le substrat sans mouvement lateral, selon une droite definie par l'appui de la racle sur l'ecran. A ['avant et a l'arriere de cette droite de contact selon le sens de deplacement de la racle, l'ecran ne touche pas le substrat ce qui permet d'obtenir une separation parfaitement controlee progressive et homogene entre le substrat et l'ecran alors que la finesse de la maille et la rheologie des encres vent choisies de telle maniere que le transfert a travers l'ecran ntaie lieu qu'au niveau de la droite de contact entre le o substrat et ledit ecran. Par contre, lorsque l'on cherche a appliquer la serigraphie hors contact a un pochoir constitue par exemple d'une feuille metallique de 150 microns d'epaisseur tendue sur un cadre et dans le but de serigraphier un produit visqueux, la problematique est differente. En effet, dans ce cas, le contact entre le pochoir et le substrat ne se limite pas a une droite mais a une surface mal controlee, car contrairement a un ecran a maille tisse, ce type de pochoir admet une certaine flexibilite mais aucune elasticite, ce qui se traduit par un rayon de courbure tres grand assimilable a un plan et ceci a pour consequence une separation entre le pochoir et le substrat qui s'effectue pendant une duree et un mouvement non contr81e done non reproductible. De plus, ce mauvais contact entre le pochoir et le substrat cree une pollution de la face inferieure du pochoir par du produit qui est transfere sur ['avant de la zone de contact a travers les ouvertures du pochoir. Du fait de sa non-elasticite, le pochoir est soumis a des contraintes et a des deplacements lateraux. Ceci conduit a la formation de depots partiels et a des courts-circuits. D'autre part, comme le pochoir est tendu dans le cadre a ['aide d'une liaison elastique constituee soit d'une maille en polyester ou en acier inoxydable 2s ou encore de ressorts, il sten suit que ['image imprimee est decalee selon que l'on imprime dans un sens ou dans le sens oppose. Les inconvenients de la serigraphie hors contact ont quasiment conduit a l'abandonner et a creer un consensus pour la serigraphie en contact lorsqutil est fait usage de pochoirs metalliques. Par contre, il apparait que la serigraphie en contact bien qu'elle limite les problemes de pollution de la face inferieure du pochoir, ne regle en rien les problemes de demoulage des plots de produit et de decalage d'image. En effet, ['adhesion des produits visqueux sur le pochoir et le substrat genere un mouvement de separation qui demarre en general sur les bords du substrat pour finir au centre. La tension importante du pochoir se traduit par des efforts lateraux considerables ainsi qu'a des micro-deplacements du pochoir par rapport au substrat qui tendent a cisailler les plots en cours de demoulage. De plus, la partie centrale du substrat est soumise a un decollement brutal et incontrble qui conduit de fac,on aleatoire a re s entramer du produit dans le pochoir. Dans certains cas ce decollement brutal conduit a mettre le pochoir en vibration a la maniere d'une peau de tambour et celui-ci peut done revenir en contact avec le substrat apres la separation, ce qui a pour effet de deteriorer certains depOts qui avaient ete demoules de maniere satisfaisante. Pour eviter cela, et tenter de generer un demoulage plus simultane, on peut augmenter la vitesse de o separation entre le pochoir et le substrat. Mais ceci genere un effet pervers car on ne laisse pas le temps a l'air de passer sous le pochoir et par consequent le pochoir est plaque sur le substrat par une depression qui va etre annulee brutalement et contribuer The stencils used are made up of a solid metal or plastic sheet, stretched by its four sides on a frame and in which wind makes openings at locations where a deposit must be made. Screen printing therefore consists of affixing the stretched stencil to the substrate and of forcing the product through the stencil openings using a transfer member which may be an inclined doctor blade or a closed injection device moved in place. press on the surface of the stencil, then the substrate and the stencil are separated for the purpose of removing the screen-printed substrate and replacing it with another to be treated. There are two types of stencil screen printing, the first which is also the most used, consists of working in contact, which means that the stencil rests on the entire surface of the substrate during the filling phase of the put openings, when all the openings when the wind is full, all the deposits are removed from the mold by moving the stretched mask away in a movement perpendicular to the substrate. The second mode of screen printing consists in working without contact, that is to say that the stencil is approached at a distance of a few tenths of a millimeter from the substrate. Then when the transfer member is brought to bear on the stencil, it pushes the stencil in contact with the substrate in the support area as it moves and simultaneously there is a movement of separation of the stencil and substrate at the back of the transfer member. Both modes of screen printing have a number of advantages and disadvantages. The non-contact mode is unanimously used for serigraphy of liquid inks using woven screens as practiced for printing posters or tissue. Indeed, in this case, use is not made of stencils but of screens made up of a woven mesh blocked in places which should not receive ink. Mesh screens look good on non-contact screen printing because their flexibility combined with their elasticity allow intimate contact between the mask and the substrate without lateral movement, along a line defined by the support of the doctor blade on the screen. At the front and at the rear of this contact line according to the direction of displacement of the doctor blade, the screen does not touch the substrate, which makes it possible to obtain a perfectly controlled gradual and homogeneous separation between the substrate and the screen while the fineness of the mesh and the rheology of the inks are chosen in such a way that the transfer through the screen takes place only at the level of the line of contact between the substrate and said screen. On the other hand, when one seeks to apply screen printing without contact to a stencil consisting for example of a metal sheet 150 microns thick stretched over a frame and for the purpose of screen printing a viscous product, the problem is different. Indeed, in this case, the contact between the stencil and the substrate is not limited to a straight line but to a poorly controlled surface, because unlike a screen with woven mesh, this type of stencil admits a certain flexibility but no elasticity, which results in a very large radius of curvature comparable to a plane and this results in a separation between the stencil and the substrate which takes place for a period of time and an uncontrolled movement therefore non reproducible. In addition, this poor contact between the stencil and the substrate creates pollution of the lower face of the stencil by product which is transferred to the front of the contact zone through the openings of the stencil. Due to its non-elasticity, the stencil is subjected to stresses and lateral displacements. This leads to the formation of partial deposits and to short circuits. On the other hand, as the stencil is stretched in the frame using an elastic connection made up either of a polyester or 2s stainless steel mesh or of springs, it follows that the printed image is offset depending on whether one prints in one direction or in the opposite direction. The disadvantages of non-contact screen printing have almost led to abandoning it and creating a consensus for contact screen printing when metallic stencils are used. On the other hand, it appears that screen printing in contact, although it limits the problems of pollution of the lower face of the stencil, does not in any way solve the problems of demolding of the product pads and image shifting. In fact, the adhesion of viscous products to the stencil and the substrate generates a separation movement which generally starts at the edges of the substrate and ends up in the center. The significant tension of the stencil results in considerable lateral forces as well as micro-displacements of the stencil relative to the substrate which tend to shear the studs during demolding. In addition, the central part of the substrate is subjected to a brutal and uncontrollable detachment which leads in a random manner to re-enter the product in the stencil. In some cases this abrupt detachment leads to the stencil vibrating in the manner of a drum skin and it can therefore come back into contact with the substrate after separation, which has the effect of deteriorating certain deposits which had been molds satisfactorily. To avoid this, and to try to generate a more simultaneous demolding, one can increase the speed of separation between the stencil and the substrate. But this generates a perverse effect because we do not allow time for the air to pass under the stencil and therefore the stencil is plated on the substrate by a depression which will be abruptly canceled and contribute

ainsi a une separation subite et totalement aleatoire. thus to a sudden and totally random separation.

I1 appara^t que la tension importante qu'il faut appliquer au pochoir, afin de minimiser les mouvements lateraux de ce dernier en cours de serigraphie, sans toutefois les supprimer completement, genere des variations de tension importantes en It appears that the significant tension which must be applied to the stencil, in order to minimize the lateral movements of the latter during screen printing, without however completely eliminating them, generates significant variations in tension in

cours de demoulage et entrane des micro-deplacements parasites. demoulding course and causes parasitic micro-displacements.

Dans le cas d'une serigraphie a ['aide d'un pochoir metallique monte tendu sur un cadre selon ses quatre cates, il appara^t un probleme lie a la non-elasticite du pochoir ainsi qu'a sa rigidite. De maniere generale, pour un pochoir metallique tendu par deux ou par quatre cotes, la moindre force qui ntest pas appliquee selon le plan du pochoir a ltetat tendu, conduit a des deplacements lateraux aleatoires et a des ondulations du pochoir, done a une non matrise du depat ainsi realise. Ces ondulations et deplacements aleatoires vent egalement liees au caractere hyperstatique de la liaison 2s pochoir/cadre. De par la nature du materiau, les seules deformations non permanentes ma^trisables qu'il est possible d'appliquer a un clinquant metallique vent des deformations selon une surface reglee, comme par exemple, une surface cylindrique. Par consequent, le fait d'appliquer une tension sur deux ou quatre cOtes selon un plan et d'appliquer une force ayant une composante perpendiculaire a ce plan par le biais de la racle dans le cas d'une serigraphie hors contact, ou lors du demoulage par ['adhesion du produit serigraphie sur le pochoir dans le cas d'une serigraphie en contact, cree immanquablement des ondulations et des micro-deplacements du pochoir. Comme cela a ete dit precedemment, ces ondulations se traduisent par un defaut de contact entre le po choir et le substrat vo ire meme a des deformations permanentes du pochoir et par un demoulage aleatoire et non ma^trisable. La realisation de circuits electroniques de plus en plus heterogenes et de plus en plus denses ou les plus gros composants cotoient les plus petite, conduit a la necessite de deposer des plots de creme a braser ou de colle dont ['amplitude dimensionnelle et la densite de depot staccroisent sans cesse. Dans le cas de la creme a braser cela pose un reel probleme car pour pouvoir traiter les plus petite depots qui parfois ne representent qu'un falble pourcentage du total, on do it utili ser des cremes a braser de granulometrie inferieure car le demoulage s'effectue d'une fa,con tres o aleatoire sur les plus petite depOts. L'utilisation d'une granulometrie plus faible ameliore le demoulage des plus petite depots, mais rend plus vulnerable ['ensemble du procede de brasage du fait du developpement d'une surface plus grande pour le meme volume d'alliage depose augmentant ainsi ltoxydation et conduisant a de mauvaises brasures. A ce jour, le procede de serigraphie de creme a braser sur les cartes electroniques est responsable de 60 % des defauts rencontres en fabrication, il est la premiere cause de defaillance dans ['ensemble du procede conduisant a la Fabrication de cartes electroniques. La mise en tension homogene d'une feuille metallique est delicate et des dispositifs, du type de celui decrit dans le brevet US6,067,903 ou le principe couramment utilise par l'homme de l'art qui consiste a tendre le pochoir sur le cadre par le biais d'une maille, cherchent a assurer une tension la plus importante et homogene possible en intercalant une liaison elastique entre le cadre et le pochoir, mais ne reglent en rien les problemes precedemment evoques. De plus, cette liaison elastique bien que favorable a l'homogeneisation de la tension, induit un autre inconvenient qui devient critique lors de ['operation de remplissage et de demoulage qui est un deplacement lateral du pochoir et par consequent a des depots non ma^trises et imparfaits Comme cela a ete dit precedemment, contrairement a un ecran a maille, un pochoir metallique ne presente aucune elasticite. Par consequent, lorsque lors du demoulage, le masque est entra^me par le substrat, on cree immanquablement un mouvement lateral du pochoir. Ce mouvement lateral selon les dispositions du pochoir et du substrat peut atteindre plusieurs dizaines de microns. Ainsi, en cours de demoulage, les plots non demoules subissent un mouvement lateral qui a pour effet de cisailler le plot a l' interface du substrat et du pochoir, ce qui va se traduire par un re-entramement In the case of a serigraphy using a metal stencil mounted stretched on a frame according to its four sides, there appears a problem linked to the non-elasticity of the stencil as well as to its rigidity. Generally, for a metal stencil stretched by two or by four sides, the slightest force which is not applied according to the plan of the stencil in the stretched state, leads to random lateral displacements and to undulations of the stencil, therefore to an uncontrolled of the depat thus realized. These ripples and random movements are also linked to the hyperstatic nature of the 2s stencil / frame connection. By the nature of the material, the only non-permanent controllable deformations which it is possible to apply to a metallic foil are deformations according to a set surface, such as for example a cylindrical surface. Consequently, the fact of applying a tension on two or four sides along a plane and of applying a force having a component perpendicular to this plane by means of the doctor blade in the case of a screenprinting without contact, or during the demolding by adhesion of the product screen printed on the stencil in the case of a screen printing in contact, inevitably creates undulations and micro-displacements of the stencil. As has been said previously, these undulations result in a lack of contact between the stencil and the substrate or even in permanent deformations of the stencil and in a random and non-controllable demolding. The realization of increasingly heterogeneous and increasingly dense electronic circuits where the largest components are next to the smallest, leads to the need to deposit pads of soldering cream or glue whose dimensional amplitude and density depot are constantly increasing. In the case of soldering cream this poses a real problem because to be able to treat the smallest deposits which sometimes represent only a small percentage of the total, we have to use soldering creams of lower particle size because the demolding is performed in a con, very random fashion on the smallest deposits. The use of a smaller particle size improves the demolding of the smallest deposits, but makes the whole brazing process more vulnerable due to the development of a larger surface for the same volume of alloy deposited, thereby increasing oxidation and leading to poor soldering. To date, the process of screen printing of soldering cream on electronic cards is responsible for 60% of faults encountered in manufacturing, it is the first cause of failure in the whole process leading to the manufacturing of electronic cards. The homogeneous tensioning of a metal sheet is delicate and devices, of the type described in patent US Pat. No. 6,067,903 or the principle commonly used by those skilled in the art which consists in stretching the stencil on the frame by through a mesh, seek to ensure the greatest possible and homogeneous tension possible by interposing an elastic connection between the frame and the stencil, but in no way resolve the problems previously mentioned. In addition, this elastic link, although favorable for the homogenization of the tension, induces another drawback which becomes critical during the filling and demolding operation which is a lateral displacement of the stencil and consequently at unmodified deposits. trises and imperfect As has been said above, unlike a mesh screen, a metal stencil has no elasticity. Consequently, when during the demolding, the mask is entrained by the substrate, an lateral movement of the stencil is inevitably created. This lateral movement according to the arrangements of the stencil and the substrate can reach several tens of microns. Thus, during demolding, the unmolded pads undergo a lateral movement which has the effect of shearing the pad at the interface of the substrate and the stencil, which will result in a re-entraming

aleatoire du produit dans le pochoir. random product in the stencil.

DESCRIPTION DE L'INVENTIONDESCRIPTION OF THE INVENTION

De cette description de l' art anterieur et des problemes qu' il en ressort la From this description of the prior art and the problems which arise therefrom

presente invention vise a apporter une solution en traitant separement les phases de remplissage et de demoulage. L' invention se caracterise essentiellement en une dissociation du traitement de ces deux operations dans la facon dont s'opere la mise en ccuvre du pochoir pour chacune de ces deux phases. Par rapport a l'art anterieur ou la structure de mise en aeuvre est commune pour les phases de remplissage et de 0 demoulage, dans la presente invention, la structure de mise en ccuvre permet d'adapter sequentiellement une structure specifique a la phase remplissage et une structure present invention aims to provide a solution by separately treating the filling and demolding phases. The invention is essentially characterized by a dissociation of the processing of these two operations in the way in which the stencil is implemented for each of these two phases. Compared to the prior art where the implementation structure is common for the filling and demolding phases, in the present invention, the implementation structure makes it possible to sequentially adapt a specific structure to the filling phase and a structure

specifque a la phase de demoulage.specific to the demolding phase.

De facon generale le remplissage du pochoir s'effectue en contact plan et le demoulage s'effectue de facon progressive sans contrainte laterale. L' invention se caracterise essentiellement en ce que le pochoir est maintenu et bloque lateralement en contact plan sur le substrat durant la phase de remplissage des orifices du pochoir et que la separation du pochoir et du substrat est realisee de facon progressive par soulevement du pochoir sans appliquer de tension laterale sur le pochoir de part ses extremites. Ceci ameliore significativement la qualite du depot. L' invention consiste done a dissocier le Generally the filling of the stencil is done in plan contact and the demoulding is done in a progressive way without lateral constraint. The invention is essentially characterized in that the stencil is maintained and laterally blocked in plane contact on the substrate during the filling phase of the stencil orifices and that the separation of the stencil and the substrate is carried out gradually by lifting the stencil without apply lateral tension to the stencil from its ends. This significantly improves the quality of the deposit. The invention therefore consists in dissociating the

kaitement de la phase de remplissage du pochoir et celui de la phase de demoulage. treatment of the filling phase of the stencil and that of the demolding phase.

Selon une autre caracteristique de ['invention durant ['operation de remplissage, le pochoir est tendu par ses extremites de facon a ce qu'il forme un plan parallele au plan du substrat, la tension doit etre suffisante pour que ['effort transversal genere par l'organe de remplissage ne provoque pas de glissement du pochoir par According to another characteristic of the invention during the filling operation, the stencil is stretched by its ends so that it forms a plane parallel to the plane of the substrate, the tension must be sufficient for the transverse force generated by the filling member does not cause the stencil to slip by

2s rapport au substrat.2s compared to the substrate.

Afin de garantir un blocage transversal complet du pochoir en cours de remplissage, au moins deux elements de maintien vent disposes a ['avant et a l'arriere de la zone de transfert. Lorsque le remplissage est effectue et selon une autre caracteristique de ['invention, pour pouvoir proceder a ltoperation de demoulage, on reduit, voire on annule la tension sur les exkemites du pochoir en leur laissant la possibilite de se deplacer lateralement. Ainsi, au fur et a mesure de l'eloignement du substrat par rapport au pochoir, on genere un demoulage progressif sans contrainte laterale par In order to guarantee a complete transverse blocking of the stencil during filling, at least two wind holding elements arranged at the front and at the rear of the transfer zone. When the filling is carried out and according to another characteristic of the invention, in order to be able to carry out the release of the mold, the tension on the ends of the stencil is reduced, or even canceled, leaving them the possibility of moving laterally. Thus, as the substrate moves away from the stencil, a progressive demoulding is generated without lateral stress by

accompagnement du substrat par le pochoir. support of the substrate by the stencil.

Selon une autre caracteristique de ['invention, afin d'eviter que le pochoir ne flechisse de fa,con trop importante lors du demoulage, il est judicieux de maintenir les extremites du pochoir sans les bloquer et/ou de supporter le pochoir au moins a ['avant et a l'arriere de la zone a serigraphier de maniere a soulever le pochoir According to another characteristic of the invention, in order to prevent the stencil from flexing too much, con too large during demolding, it is advisable to maintain the ends of the stencil without blocking them and / or to support the stencil at least a ['front and back of the area to be screen printed so as to lift the stencil

perpendiculairement relativement au substrat. perpendicular to the substrate.

Selon une autre caracteristique de ['invention, en cours de remplissage et jusqu'a ['operation de demoulage, afin d'eviter tout mouvement de glissement parasite entre le pochoir et le substrat, en particulier au moment de relacher la tension sur les extremites du pochoir celui-ci peut 8tre bloque de maniere complete au niveau du plan du substrat par le biais d'elements de maintien sans generer d'effort lateral sur le pochoir, par exemple, par pincement et/ou aspiration du pochoir au moins a ['avant et a According to another characteristic of the invention, during filling and until the demolding operation, in order to avoid any parasitic sliding movement between the stencil and the substrate, in particular when releasing the tension on the ends. the stencil can be blocked completely at the level of the substrate plane by means of holding elements without generating lateral force on the stencil, for example, by pinching and / or aspiration of the stencil at least at [ before and a

l'arriere de la zone a serigraphier. the back of the area to be screen printed.

Le dispositif selon la presente invention permet done non seulement d'effectuer un remplissage sans mouvement lateral du pochoir, mais egalement un demoulage de meilleure qualite car il s'effectue selon un mouvement de soulevement du pochoir par rapport au substrat, ce qui diminue les surfaces de contact. Le mouvement de separation est ainsi non seulement parfaitement controle et ma^trise mais de plus le demoulage est effectue dans des conditions optimum pcisqu'il est realise sans contrainte laterale. Comme cela a ete explique precedemment dans les dispositifs de l'art anterieur, le mouvement de separation entre le substrat et le pochoir est obtenu en combinant l'eloignement de l'un par rapport a l'autre et la tension du pochoir. Or ['effort lateral genere sur le pochoir par le cadre sur lequel ce dernier est monte tendu provoque 2s immanquablement des contraintes laterales sur les depots et par consequent, des demoulages imparfaits. Un objet de la presente invention est done de minimiser au maximum voire d'annuler toutes les contraintes laterales en cours de demoulage. A cet effet, le mouvement de demoulage est obtenu, apres annulation de la tension exercee sur le pochoir et par soulevement de ce dernier relativement au substrat a ['aide d'un support de pochoir qui est dispose sous le pochoir au moins a ['avant et a l'arriere de la zone a serigraphier. Ainsi la separation entre le pochoir et le substrat s'opere de fa,con progressive selon une ligne de separation qui se deplace de la peripherie vers le centre du substrat. Dans la mesure ou l'on ntapplique pas de tension sur le pochoir et que ses extremites peuvent se deplacer lateralement, on ne genere pas de contraintes laterales sur la zone du pochoir qui demeure en contact avec le substrat a cet instant. En fait localement, le demoulage s'opere selon un mouvement de rotation autour de la ligne de s separation, sans contrainte laterale sur le plot de produit a deposer. Les seuls efforts sur le plot au moment du demoulage vent done ['adherence du plot sur le substrat et sur le pochoir. Ces deux forces vent done opposees et ont une direction perpendiculaire au substrat. Selon une autre caracteristique de ['invention, elle peut fonctionner de o facon alternative dans les deux sens d'avance du dispositif de transfert et a cet effet il est extremement avantageux de la mettre en oeuvre sur une machine a serigraphier comme par exemple celles utilisees en assemblage electronique pour le depot de produits visqueux. Il est entendu egalement que selon l'equipement de serigraphie utilise, la separation relative du pochoir et du substrat peut etre obtenue soit en abaissant le The device according to the present invention therefore makes it possible not only to perform a filling without lateral movement of the stencil, but also a better quality release from the mold because it is carried out in a lifting movement of the stencil relative to the substrate, which reduces the surfaces of contact. The separation movement is thus not only perfectly controlled and controlled, but also the demolding is carried out under optimum conditions as it is carried out without lateral stress. As has been explained previously in the devices of the prior art, the separation movement between the substrate and the stencil is obtained by combining the distance from one with respect to the other and the tension of the stencil. Now the lateral force generated on the stencil by the frame on which the latter is mounted stretched 2s inevitably causes lateral stresses on the deposits and consequently, imperfect mold release. An object of the present invention is therefore to minimize as much as possible or even to cancel all the lateral stresses during demolding. To this end, the demolding movement is obtained, after the tension exerted on the stencil has been canceled and by lifting the latter relative to the substrate using a stencil support which is placed under the stencil at least at [' front and back of the area to be screen printed. Thus the separation between the stencil and the substrate takes place in a progressive fashion along a separation line which moves from the periphery towards the center of the substrate. Insofar as one does not apply tension to the stencil and its ends can move laterally, one does not generate lateral stresses on the area of the stencil which remains in contact with the substrate at this instant. In fact locally, the demoulding takes place in a rotational movement around the separation line, without lateral stress on the pad of product to be deposited. The only efforts on the pad at the time of demolding are therefore done by the adhesion of the pad to the substrate and to the stencil. These two forces are therefore opposite and have a direction perpendicular to the substrate. According to another characteristic of the invention, it can operate in an alternative way in both directions of advance of the transfer device and for this purpose it is extremely advantageous to use it on a screen printing machine such as those used in electronic assembly for the deposit of viscous products. It is also understood that depending on the screen printing equipment used, the relative separation of the stencil and the substrate can be obtained either by lowering the

substrat par rapport au pochoir, soit en soulevant le pochoir par rapport au substrat. substrate relative to the stencil, or by lifting the stencil relative to the substrate.

Evidemment les deux modes de fonctionnement vent couverts par la presente invention. Obviously the two wind operating modes covered by the present invention.

D'autres caracteristiques de la presente invention appara^tront a la lecture Other characteristics of the present invention will appear on reading

de la description des figures qui representent des exemples de realisation non limitatifs. of the description of the figures which represent nonlimiting exemplary embodiments.

En figure 1, est represente schematiquement une operation de demoulage In FIG. 1, a demolding operation is represented diagrammatically

selon l'art anterieur.according to the prior art.

En fgure 2, est represente schematiquement une operation de demoulage In figure 2, a demolding operation is represented diagrammatically

selon ['invention.according to the invention.

En figure 3 est represente l'avantage donne par le mouvement de In Figure 3 is represented the advantage given by the movement of

soulevement prouvant une diminution des surfaces en contact. lifting proving a decrease in contact surfaces.

En figure 4, est represente en coupe un exemple de dispositif avec In Figure 4, is shown in section an example of a device with

soulevement des deux cOtes.lifting of both sides.

En figure 5, est represente un pochoir selon la presente invention. In Figure 5, there is shown a stencil according to the present invention.

En figure 6, est represente une autre forme de mise en ccuvre du dispositif In Figure 6, is represented another form of implementation of the device

avec soulevement d'un seul cote.with lifting on one side.

La figure 1 represente schematiquement dans un plan les forces induites Figure 1 shows schematically in a plane the induced forces

sur une portion elementaire A du pochoir (1), lors d'un demoulage selon l'art anterieur. on an elementary portion A of the stencil (1), during demolding according to the prior art.

Comme on peut le voir en figure la, apres remplissage, A subit deux forces T1 et T2 de modules et de direction identique mais de sens opposes. Ces forces T1 et T2 vent liees a la tension du pochoir generee par la liaison (14) avec le cadre (13). Lorsqu'en figure lb, le pochoir (1) est eloigne relativement au substrat (4), le pochoir est entrame par ce dernier par [' adherence du produit serigraphie, ce qui a pour effet d' augmenter le module de T1. Puis lorsque la tension T1 devient suffisamment importante et que sa composante verticale est equivalente aux forces d' adherence, le pochoir est arrache a la surface du substrat. En fait, lors de la separation, le module de T1 augmente alors que sa direction s' incline d' un angle 0 par rapport a l'horizontale. T 1 augmente car lors d'un 0 demoulage la distance entre le cadre (13) et le point A a tendance a augmenter et que la liaison (14) n'est pas un ressort a effort constant. Pour conserver l'equilibre, il faut done forcement que le substrat applique une reaction R. telle que la somme geometrique des , _ vecteurs T1, T2 et R soit nulle. Comme on peut le constater, la reaction R du substrat presente une composante verticale qui correspond sensiblement aux forces d'adherence du produit sur le substrat pour la portion de pochoir consideree. Par contre, R comporte egalement une composante horizontale qui a tendance a provoquer un mouvement de glissement du pochoir sur le substrat. Le deplacement horizontal du pochoir va dependre de ['adherence du produit sur le substrat ainsi que de la position de la portion de pochoir consideree, mais elle atteint facilement une valeur superieure a lOIl, ce qui est extremement important pour des ouvertures de l'ordre de 20011. Ce deplacement relatif entre le po choir et le sub strat genere deux effete nefastes qui sont, d'une part une pollution de la face inferieure du pochoir et de la surface du substrat, et d'autre part, un cisaillage des plots au moment de la separation du pochoir et du substrat, ce qui se traduit par un re-entramement total ou partiel de produit dans le pochoir. On peut constater egalement que les efforts qu'il faut mettre en aeuvre pour parvenir a creer une composante verticale de R suffisante pour provoquer l'arrachement du pochoir par rapport au substrat, vent extremement importants. A titre d'exemple, pour un angle de 0,5 et pour vaincre un effort d'adherence de 1 g, il faut appliquer une traction T1 de 115 g. Sachant que pour ['ensemble d'un pochoir ['effort d'adherence peut atteindre une valeur de l'ordre du kilogramme, on s'aper,coit que les efforts de traction en jeu vent enormes par rapport au besoin reel qui est uniquement la composante verticale. De plus, [' effort d' adherence global sur le pochoir varie tres rapidement lors d' un demoulage en fonction du nombre d' ouvertures en cours de demoulage a un instant donne ce qui implique des variations brutales des efforts lateraux sur le pochoir et done a des efforts lateraux sur les dep8ts en cours de As can be seen in Figure la, after filling, A undergoes two forces T1 and T2 of modules and identical direction but opposite directions. These forces T1 and T2 are related to the tension of the stencil generated by the connection (14) with the frame (13). When in FIG. 1b, the stencil (1) is moved away relative to the substrate (4), the stencil is opened by the latter by the adhesion of the screen-printed product, which has the effect of increasing the modulus of T1. Then when the tension T1 becomes sufficiently large and its vertical component is equivalent to the adhesion forces, the stencil is torn off from the surface of the substrate. In fact, during separation, the module of T1 increases while its direction is inclined by an angle 0 with respect to the horizontal. T 1 increases because during a demolding 0 the distance between the frame (13) and the point A tends to increase and that the connection (14) is not a spring with constant force. To maintain equilibrium, the substrate therefore necessarily has to apply a reaction R. such that the geometric sum of the vectors _, T1, T2 and R is zero. As can be seen, the reaction R of the substrate has a vertical component which corresponds substantially to the adhesion forces of the product on the substrate for the portion of stencil considered. On the other hand, R also has a horizontal component which tends to cause a sliding movement of the stencil on the substrate. The horizontal displacement of the stencil will depend on the adhesion of the product to the substrate as well as the position of the portion of stencil considered, but it easily reaches a value greater than 10, which is extremely important for openings of the order of 20011. This relative displacement between the stencil and the sub strat generates two harmful effects which are, on the one hand a pollution of the lower face of the stencil and the surface of the substrate, and on the other hand, a shearing of the studs at the time of separation of the stencil and the substrate, which results in a total or partial re-entraming of product in the stencil. It can also be seen that the efforts that have to be made to succeed in creating a vertical component of R sufficient to cause the stencil to be torn away from the substrate, are extremely important. For example, for an angle of 0.5 and to overcome an adhesion force of 1 g, it is necessary to apply a traction T1 of 115 g. Knowing that for the set of a stencil the adhesion effort can reach a value of the order of a kilogram, we realize that the traction efforts in play are enormous compared to the real need which is only the vertical component. In addition, the overall adhesion force on the stencil varies very quickly during demolding depending on the number of openings being demolded at a given time which implies sudden variations in lateral forces on the stencil and therefore to lateral forces on the dep8ts during

s demoulage.s mold release.

La figure 2 represente schematiquement dans un plan, les forces induites sur une portion elementaire A du pochoir (1) en cours de demoulage sur un pochoir et son dispositif de mise en acuvre selon la presente invention. Dans ce cas, apres remplissage les efforts appliques sur A vent nuls, abstraction faite de la pesanteur. Puis o lorsque le pochoir est eloigne relativement au substrat (4) sous ['action du support de pochoir (15), A est soumis a un effort de soulevement S et a la reaction du substrat R directement oppose. Comme on peut le voir, dans ce cas, aucun effort lateral parasite ntest applique ce qui permet une separation progressive sans mouvement de glissement du pochoir sur le substrat. Les efforts mis en jeu ici correspondent aux efforts Figure 2 shows schematically in a plane, the forces induced on an elementary portion A of the stencil (1) being demolded on a stencil and its implementation device according to the present invention. In this case, after filling the forces applied to zero wind, apart from gravity. Then, when the stencil is moved away relative to the substrate (4) under the action of the stencil support (15), A is subjected to a lifting force S and to the reaction of the substrate R directly opposite. As can be seen, in this case, no parasitic lateral force is applied which allows a gradual separation without sliding movement of the stencil on the substrate. The efforts put into play here correspond to the efforts

s d' adherence du produit dans le pochoir. s adhesion of the product in the stencil.

La figure 3 montre l'avantage qu'il y a a effectuer un demoulage selon un mouvement de soulevement et sans imprimer une tension au pochoir. Comme on peut le voir, l'enlevement du pochoir (1) par soulevement selon une surface plus ou moins cylindrique permet de reduire la surface d' adherence entre les plots (6) du produit (7) et les orifices (5) du pochoir. En effet, pour que le demoulage puisse avoir lieu, il faut que la surface occupee par le plot (6) sur le substrat (4), divisee par la surface des parois de ['orifice (5), soit superieure a une certaine valeur. Par exemple, pour un depOt de creme a braser selon un mode de serigraphie en contact, on s'accorde a dire que ce rapport doit etre superieur a 0,66 pour avoir un demoulage acceptable et repetitif. Selon le mode de 2s dep8t de la presente invention, le demoulage d'un plot (6) n'est pas fait de fa,con simultanee mais par soulevement progressif du pochoir sans appliquer de contrainte laterale au depot. En fait, on commence par decoller un cOte du plot, pcis progressivement le plot complet. Cette facon de faire revient done a diminuer la surface d' adherence du produit (7) dans ['orifice (5), or la force de reentramement du produit par le pochoir est precisement proportionnelle a cette surface d' adherence. Ainsi, des essais de mise en oeuvre de la presente invention ont permis de montrer que le rapport surface occupee par le plot (6) divisee par la surface des parois de ['orifice (5) pouvait Figure 3 shows the advantage that there is to perform a demolding according to a lifting movement and without imparting tension to the stencil. As can be seen, the removal of the stencil (1) by lifting along a more or less cylindrical surface makes it possible to reduce the surface of adhesion between the pads (6) of the product (7) and the orifices (5) of the stencil . In fact, for demolding to take place, the surface occupied by the stud (6) on the substrate (4), divided by the surface of the walls of the orifice (5), must be greater than a certain value. . For example, for a deposition of soldering cream according to a contact screen printing mode, it is agreed that this ratio must be greater than 0.66 in order to have an acceptable and repetitive demolding. According to the mode of 2s dep8t of the present invention, the demoulding of a pad (6) is not done in a simultaneous manner, but by progressive lifting of the stencil without applying lateral stress to the deposit. In fact, we start by taking off one side of the plot, then gradually the complete plot. This way of doing therefore amounts to reducing the surface area of adhesion of the product (7) in the orifice (5), but the force of reentramation of the product by the stencil is precisely proportional to this surface area of adhesion. Thus, tests of implementation of the present invention have made it possible to show that the ratio of area occupied by the stud (6) divided by the area of the walls of the orifice (5) could

etre reduit de 25 % sans nuire a la qualite et a la repetitivite des depOts ainsi obtenus. be reduced by 25% without affecting the quality and repetitivity of the deposits thus obtained.

La figure 4 represente un exemple non limitatif de dispositif conforme a la presente invention. En figure 4a est represente la phase de remplissage du pochoir (1) s a ['aide d'un organe de transfert (2), qui ici est un dispositif d'injection ferme mais qui peut egalement etre une racle connue par lthomme de ['art, celui-ci est deplace dans le FIG. 4 represents a nonlimiting example of a device according to the present invention. In Figure 4a is shown the filling phase of the stencil (1) sa ['using a transfer member (2), which here is a closed injection device but which can also be a doctor blade known by the man of [' art, this one is moved in the

sens (D 1) et remplit les ouvertures (5) du pochoir au fur et a mesure de son avancement. direction (D 1) and fills the openings (5) of the stencil as it progresses.

Pendant cette phase de remplissage, le pochoir (1) est maintenu fixe dans le plan forme par le substrat (4) par un dispositif donne a titre d'exemple non limitatif. La force de o maintien laterale est assuree par les actionneurs pilotables qui ici vent des verins (9) qui provoquent une tension du pochoir (1) suffisante afin d'eviter tout mouvement de glissement du pochoir (1) par rapport au substrat (4) lie a l'avancement du dispositif de transfert (2). En 4b, est representee ['operation de demoulage durant laquelle on procede a la separation progressive du subskat relativement au pochoir. Pour ne pas generer d'efforts lateraux sur les depOts (6) en cours de demoulage et ainsi permettre un demoulage optimum, la tension appliquee par le biais des verins (9) est diminuee, voire supprimee, de maniere a liberer les extremites du pochoir (1). Ainsi le demoulage des depOts (6) correspondent aux orifices (5) steffectue progressivement par soulevement en diminuant les surfaces d'adherence grace a un mouvement angulaire du pochoir qui accompagne le substrat dans son mouvement vertical. Evidemment le dispositif peut During this filling phase, the stencil (1) is kept fixed in the plane formed by the substrate (4) by a device given by way of nonlimiting example. The force of lateral support is provided by the controllable actuators which here wind cylinders (9) which cause a sufficient tension of the stencil (1) in order to avoid any movement of sliding of the stencil (1) relative to the substrate (4). linked to the advancement of the transfer device (2). In 4b, is represented the demolding operation during which one proceeds to the progressive separation of the subskat relative to the stencil. In order not to generate lateral forces on the deposits (6) during demolding and thus allow optimum demolding, the tension applied by means of the jacks (9) is reduced, or even eliminated, so as to release the ends of the stencil. (1). Thus the release of the deposits (6) correspond to the orifices (5) steffectue gradually by lifting by decreasing the adhesion surfaces thanks to an angular movement of the stencil which accompanies the substrate in its vertical movement. Obviously the device can

egalement fonctionner dans le sens (D2). also work in direction (D2).

Dans le cas represente, la tension en cours de remplissage est assuree par quatre actionneurs pilotables ou verins situes dans les quatre angles du pochoir (1) et fixes par les trous (10); leur fonction est de maintenir lateralement le pochoir en cours de remplissage, mais egalement de le positionner lateralement en vue de son alignement avec le substrat a serigraphier. A cet effet, des butees non representees permettent de repositionner le pochoir systematiquement dans la meme position. D'autres dispositions des actionneurs vent envisageables sans sortir du champ d' application de la presente invention. De plus, selon une autre caracteristique de ['invention, afin d'eviter tout mouvement lateral du pochoir en cours de remplissage, le maintien lateral en cours de transfert, est complete par un blocage complet obtenu par deux elements de maintien par aspiration (12) solidaires du cadre et disposes a la surface du pochoir (1) au moins a l' avant et a l'arriere de la zone de transfert. Lorsque le vice est applique dans les elements de maintien a ['aide d'un dispositif non represente, le pochoir (1) est plaque contre lesdits elements de maintien. Ainsi le pochoir est maintenu en position sans induire de contrainte laterale au moment de ['activation de ce maintien ou au moment de sa desactivation. Les elements de maintien (12) permettent done de garantir un blocage lateral complet du masque durant ['operation de remplissage, mais egalement d'empecher tout mouvement lateral du pochoir avant l'etape de demoulage au moment de relacher la tension du pochoir. Ainsi ce n'est qu'apres avoir relache la tension du o pochoir (1) que les elements de maintien vent desactives de maniere a liberer les extremites du pochoir de toute contrainte laterale. A cet effet, il peut etre avantageux de creer une surpression au niveau des elements de maintien de maniere a creer un coussin d'air entre ces derniers et le pochoir et minimiser ainsi les forces laterales parasites sur le pochoir au moment de lteloignement relatif du substrat par rapport au pochoir. Le support de pochoir (15), qui est ici realise a ['aide de deux barres fixees sur les elements de maintien, permet a la fois de maintenir le pochoir (1) contre les elements de maintien mais egalement comme on peut le voir en 4b, de soulever le pochoir (1) non tendu afin In the case shown, the tension during filling is provided by four controllable actuators or jacks located in the four corners of the stencil (1) and fixed by the holes (10); their function is to laterally maintain the stencil during filling, but also to position it laterally for alignment with the substrate to be screen printed. To this end, stops not shown make it possible to reposition the stencil systematically in the same position. Other arrangements of wind actuators can be envisaged without departing from the scope of the present invention. In addition, according to another characteristic of the invention, in order to avoid any lateral movement of the stencil during filling, the lateral support during transfer is completed by a complete blocking obtained by two suction holding elements (12 ) integral with the frame and arranged on the surface of the stencil (1) at least at the front and at the rear of the transfer zone. When the defect is applied in the holding elements using a device which is not shown, the stencil (1) is pressed against said holding elements. Thus the stencil is kept in position without inducing lateral stress at the time of activation of this maintenance or at the time of its deactivation. The holding elements (12) therefore make it possible to guarantee complete lateral locking of the mask during the filling operation, but also to prevent any lateral movement of the stencil before the demolding step when releasing the tension of the stencil. Thus it is only after having released the tension of the stencil o (1) that the wind holding elements are deactivated so as to free the ends of the stencil from any lateral stress. For this purpose, it may be advantageous to create an overpressure at the level of the holding elements so as to create an air cushion between the latter and the stencil and thus minimize the parasitic lateral forces on the stencil at the time of the relative removal of the substrate. compared to the stencil. The stencil support (15), which is produced here by means of two bars fixed on the holding elements, makes it possible both to hold the stencil (1) against the holding elements but also as can be seen in 4b, lift the non-stretched stencil (1) so

de le separer progressivement par soulevement relativement au substrat. to gradually separate it by lifting relative to the substrate.

La mise en ceuvre de ['invention consiste en un procede de depot d'un produit visqueux (7) sur un substrat (4) a travers un pochoir (1), a ['aide d'un organe de transfert (2), caracterise en ce qu'il comporte les etapes suivantes: - mise en tension du pochoir (1) par le biais de verins (9), - blocage transversal complet du pochoir (1) par le biais d' au moins deux elements de maintien (12), 2s - alignement et mise en contact du pochoir (1) par rapport au substrat (4), - remplissage du pochoir (1) a ['aide de l'organe de transfert (2), - liberation de la tension du pochoir (1) par la desactivation des verins (9), - desactivation du blocage par les elements de maintien (12), - separation du substrat et du pochoir par soulevement et accompagnement du pochoir The implementation of the invention consists of a method of depositing a viscous product (7) on a substrate (4) through a stencil (1), using the transfer member (2), characterized in that it comprises the following stages: - tensioning of the stencil (1) by means of jacks (9), - complete transverse blocking of the stencil (1) by means of at least two holding elements ( 12), 2s - alignment and contacting of the stencil (1) with respect to the substrate (4), - filling of the stencil (1) using the transfer member (2), - release of the tension of the stencil (1) by deactivating the jacks (9), - deactivation of the blocking by the retaining elements (12), - separation of the substrate and the stencil by lifting and accompanying the stencil

relativement au substrat.relative to the substrate.

Afin d' adapter le dispositif de mise en ccuvre aux differentes largeurs de substrat a traiter, ['element de maintien (12) et le support de pochoir (15) situe en vis a vis, constitue un ensemble reglable en position sur le cadre (13). In order to adapt the implementation device to the different widths of substrate to be treated, the holding element (12) and the stencil support (15) located opposite, constitutes an adjustable assembly in position on the frame ( 13).

En figure 5, est represente un pochoir (1) selon la presente invention. Les s ouvertures (5) correspondent aux zones a imprimer se situant dans la partie centrale du pochoir. Pour son positionnement lateral, son maintien et sa mise sous tension sur le cadre (13), le pochoir (1) est pourvu de trous de fixation (10). Afin de ne pas abmer le pochoir, les verins (9) vent prolonges de mors (11) qui permettent le pincement du In Figure 5, there is shown a stencil (1) according to the present invention. The openings (5) correspond to the areas to be printed located in the central part of the stencil. For its lateral positioning, its maintenance and its tensioning on the frame (13), the stencil (1) is provided with fixing holes (10). In order not to damage the stencil, the jacks (9) wind extended jaws (11) which allow the pinching of the

pochoir (1).stencil (1).

o En figure 6, selon une autre caracteristique de ['invention, le soulevement du pochoir peut etre realise sur un seul cote tandis que le cote oppose est maintenu bloque. Dans ce cas de figure, le dispositif de transfert est situe au plus proche du cote bloque. Le mouvement du pochoir doit s'effectuer sans tension par liberation o In FIG. 6, according to another characteristic of the invention, the lifting of the stencil can be carried out on one side only while the opposite side is kept blocked. In this case, the transfer device is located as close as possible to the blocked dimension. The movement of the stencil must be carried out without tension by release

progressive et sans contrainte, au fur et a mesure de la separation du substrat. progressive and without constraint, as the substrate separates.

is Selon une autre caracteristique de ['invention et pour faciliter le blocage complet du pochoir (1) durant la phase de remplissage, il peut etre judicieux de disposer les elements de maintien (12) en vis a vis des supports de pochoirs (15) et de pratiquer des ouvertures dans le pochoir dans ces zones. Ainsi, lorsque la depression est appliquee, le pochoir va etre piece entre les supports de pochoir (15) et les elements de is According to another characteristic of the invention and to facilitate complete blocking of the stencil (1) during the filling phase, it may be advisable to arrange the holding elements (12) opposite the stencil supports (15). and make openings in the stencil in these areas. Thus, when the vacuum is applied, the stencil will be part between the stencil supports (15) and the elements of

maintien.maintenance.

La description ci-dessus a ete redigee en considerant que le substrat etait The description above was written considering that the substrate was

dispose sous le pochoir. Il va de soit que le dispositif selon la presente invention peut egalement fonctionner dans d'autres configurations sans sortir du champ d'application de la presente invention. Par exemple, le pochoir peut etre dispose verticalement ou a lay out under the stencil. It goes without saying that the device according to the present invention can also operate in other configurations without departing from the scope of the present invention. For example, the stencil can be placed vertically or

2s l'envers.2s upside down.

Ainsi, le dispositif de mise en ccuvre du pochoir selon ['invention permet d'ameliorer de facon significative le demoulage en le mettant sous controle. Il permet de reduire le rapport de la surface de l'ouverture par la surface des parois de l'ouverture d'environ 25 % sans nuire a la qualite du demoulage, ce qui permet d'une part de repousser les limites de demoulage connus selon les procedes de l'art anterieur, et d'autre part d'utiliser des cremes a braser de granulometrie superieure pour le meme circuit electronique. La qualite des depots, meme les plus delicate a realiser est constante Thus, the device for implementing the stencil according to the invention makes it possible to significantly improve the mold release by putting it under control. It makes it possible to reduce the ratio of the surface of the opening by the surface of the walls of the opening by approximately 25% without harming the quality of the demolding, which allows on the one hand to push back the known demolding limits according to the processes of the prior art, and on the other hand to use soldering creams of higher particle size for the same electronic circuit. The quality of deposits, even the most delicate to achieve is constant

queues que soient leurs dispositions geographiques sur le pochoir. tails whatever their geographic arrangement on the stencil.

La presente invention permet de realiser une economic substantielle au niveau de la realisation des pochoirs de serigraphie. En effet, le pochoir accessoire de la presente invention n'a pas a etre colle sur un cadre et ne necessite pas de realiser une multitude d'ouvertures sur toute la peripherie du pochoir tel que cela est le cas pour les The present invention allows a substantial economic to be achieved in the production of screen printing stencils. Indeed, the accessory stencil of the present invention does not have to be glued to a frame and does not need to make a multitude of openings over the entire periphery of the stencil as is the case for the

systemes auto-tendeurs utilises par l'homme de l' art a ce j our. self-tensioning systems used by those skilled in the art to date.

De fa,con generale, ce type de pochoir a traitement des operations de rempli s sage et de demoulage differencie, permet de reculer le s limites de la In general, this type of stencil with processing of filling operations and differentiated demolding, allows to reduce the limits of the

o miniaturisation en assemblage electronique. o miniaturization in electronic assembly.

r t 2840850r t 2840850

Claims

1) Method for implementing a stencil (1) for depositing viscous product (7) on a substrate (4) using a transfer member (2) characterized in that the filling phase of the stencil (1) by the product (7) and the demolding phase to said product is two operations, the treatment of which is dissociated so that the stencil is kept laterally in plane contact on the substrate during the filling phase and that the separation of the stencil and the substrate is made progressively by lifting the stencil relative to the substrate without applying lateral stress

on its ends during the molding phase.

0

2) Method for using a stencil (1) for depositing viscous product (7) on a substrate (4) using a transfer member (2) according to claim 1, characterized in that the lateral holding of the stencil in planar contact on the substrate during the filling phase is completed by a blocking obtained by at least two pressure holding elements (12) located at the front and at the rear of the transfer.

3) Method for implementing a stencil (1) for depositing viscous product (7) on a substrate (4) using a transfer member (2) according to claim 1, characterized in that the separation by lifting the stencil is obtained by at least two stencil supports (15) arranged under the stencil at the front and

at the back of the transfer area.

4) Method for implementing a stencil (1) for depositing viscous product (7) on a substrate (4) using a transfer member (2) according to claim 1, characterized in that the separation of the stencil is obtained by

tension-free lifting on one side while the other side is held blocked.

5) Method for depositing a viscous product (7) on a substrate (4) through a stencil (1), using a transfer member (2), characterized in that it comprises the steps following: - tensioning of the stencil (1) by means of jacks (9), - complete transverse blocking of the stencil (1) by means of at least two holding elements (12), - alignment and contacting of the stencil (1) relative to the substrate (4), filling of the stencil (1) using the transfer member (2) release of the tension of the stencil (1) by deactivation of the jacks (9), - deactivation of the blocking by the retaining elements (12), separation of the substrate and the stencil by lifting and accompanying the stencil

relative to the substrate.

6) Method for depositing a viscous product (7) on a substrate (4) through a stencil (1), using a transfer member (2) according to claim 5, characterized in that after deactivation of the blocking by the retaining elements (12), an overpressure is applied by means of the elements (12) so as to create an air cushion between said retaining elements and the stencil in order to release the latter from the

o lateral constraints.

7) Device for depositing a viscous product on a substrate (4), using a transfer member (2) on a screen printing machine characterized in that it combines a stencil (1) provided with fixing holes (10) for maintaining and energizing it on a frame (13) and controllable actuators (9) for tensioning or respectively releasing the voltage depending on whether one is respectively in the

filling phase or in the demolding phase to said stencil.

8) Device for depositing a viscous product on a substrate (4), using a transfer member (2) on a screen printing machine according to claim 7, characterized in that locking elements by depression (12) of the stencil (1) wind arranged at least at the front and at the rear of the zone to be screen-printed and that the blocking is

active during the filling phase.

9) Device for depositing a viscous product on a substrate (4), using a transfer member (2) on a screen printing machine according to claim 7, characterized in that a stencil support ( 15) is arranged under the stencil (1) at least at the front and at the rear of the zone to be screen-printed so as to lift the stencil