MXPA97000202A - Stored for the deposit and the dosage decaps more or less thicken, based on points of a visc product - Google Patents

Abstract

The present invention relates to a stencil for depositing and dosing more or less thick layers based on dots, or in the form of dots of a viscous product on a substrate, this stencil being constituted by a solid and homogeneous sheet made of synthetic material, and provided with holes that are made by perforations, characterized in that: - the thickness of the sheet is determined as a function of the greater height of deposit that is made in the substrate, - because the sheet has different perforation diameters depending on of the height of the different tanks that must be made, said diameters being also conditioned by the thickness of the sheet, and in which the perforations constitute a deposit that is loaded in each step carried out by a doctor blade with a quantity of product of which All or part of it will be deposited on the substrate on a regular basis by close contact between the stencil and the substrate at the place where the Squeegee exerts a linear pressure and remains in front of the opening of the perforations, which allows dosing the quantities of the deposited product and controls the height of the deposits, being here different the doses of the product deposited, as well as the heights of deposit that is obtained by a step of the scratch

Description

STORED FOR THE DEPOSIT AND THE LAYER DOSAGE MORE OR * "'LESS THICKEN, BASED ON POINTS OF A VISCOSE PRODUCT.

The present invention relates to a stencil for the depositing and dosing of more or less thick layers, based on dots, of a viscous product. The present invention is situated within the technologies of surface mounting, of electronic components in printed circuit boards and in microelectronics. ^ 0 In electronic manufacturing, deposits of so-called thick layers, creams or solder pastes and dough or glue in particular, are carried out, whether by syringe or by screen printing. The deposit by syringe is a risky procedure and its productivity is limited. The the precision of its layout, the duration of its practical application and the fineness of the lines and networks that are formed, ? _4 separate this first medium from current industrial applications. Although the paste or glue can be deposited thus equipment distributors of liquids, the preferred method is silkscreen printing, using a metallic screen or screen made by chemical cutting, by laser cutting or electro-shaping. These three methods are valuable for dimensions up to 300 microns, without However, even smaller dimensions are necessary.

The use of a stencil through which "" * deposits a product, cream or solder paste that then form desired contact traces, is the most widely used procedure at industrial level. 5 At present, three types of stencils are known: the screen-woven metallic woven fabric, the silk screen woven polyester fabric and the metallic stencil. Its technical qualities are appreciated according to its performance or percentage of opening, the zone without contact and the force of j.0 applied voltage. The performance corresponds to the degree of obturation of the stencil holes, which is a function of the presence of threads in the case of woven screen. The area out of contact, or without contact, is the angle 5 that can be formed by the stencil with the support surface in working position when the doctor blade is supported. The higher this angle, the better the detachment of the viscous product from the screen. The obtaining of the zone 0 without contact, supposes a force of considerable tension of the stencil and a good coefficient of elastic deformation. According to the non-contact zone, the metallic screen printing fabric will be less good than the polyester screen printing fabric and better than a metallic screen.

The invention is essentially characterized in that the stencil for depositing and dosing the more or less thick layers based on dots or in the form of dots of a viscous product on a substrate, is constituted by a solid and homogeneous sheet of synthetic material and It has holes made by drilling. The thickness of the sheet is determined in function of the greater height of deposit that is made on the substrate, and is also characterized because the sheet has different drilling diameters depending on the height of the different deposits that are made, being conditioned these diameters also by the thickness of the sheet. Said perforations constitute a deposit that is loaded during each step by means of a scraper of a quantity of product of which all or part will be deposited on the substrate in regular form by means of close contact between the stencil and the substrate in the place where the scraper exerts a pressure linear and in front of the opening of the perforations, which allows dosing the quantities of deposited product and controlling the height of the deposits, being different the doses of the product deposited and the heights of the deposit that is obtained by means of a single step of a doctor blade. The thickness of the stencil sheet is determined according to the highest height of the workable deposit, and it has perforations of different diameter according to the doses of 2b. product that must be placed on the substrate and the tank heights, the smallest diameter being able to be of a dimension smaller than the thickness of the stencil sheet. To remedy the problems encountered in the screen screen of polyester fabric or metallic material and for the metallic stencil itself, the present invention proposes to use a ... polyester or analogous fabric, in which the fabric is no longer made up of threads, but is itself a solid sheet. This solid sheet of polyester is mechanically punched at the desired sites. The polyester fabric, since it is solid, 5 admits tensile forces superior to the metallic wire cloths and these forces are at least equal to the metallic stencils. The following description, which is presented with reference to the appended drawings for explanatory purposes and of, or in no way limiting, allows to better understand the advantages, objectives and characteristics of the present invention. Figure 1 presents the textures of masks and stencils of known types. Figure 2 presents stencil cuts and their respective qualities. • -, Figure 3 presents a view of a deposit of a thick layer. Figure 4 presents two stencils, the first having been made according to the present invention, while the other is the result of the prior art. Figure 5 shows a sectional view of a stencil according to the invention on the printed circuit board that the tanks must receive. Figure 6 represents a seen example of a plant and a simultaneous described cut of pasta or tail points with different height and diameters, depending on the type of component. Figure 7 represents a plan view with an example of constitution according to the invention of physical barriers between the 5 zones where there is a risk of bridging during the passage of the welding wave of the components. Figure 8 represents exemplary embodiments for the application of the invention, continuous lines or solid surfaces. * iQ Figure 9 represents the stenciling schematically according to the different cases of the Figures. In Figure 1 the mask and stencil textures of known types are presented. In Figure 1 we find a mesh 1 of a net 2 that is made of a weave of stainless steel wires 3, and a mesh 4 of a net 5 that is made of a weave of yarns of r r-? polyester 6. Meshes 1 and 4 have identical surfaces. On the other hand, the efficiency of the network 2 is greater than that of the network 5, since the diameters of the threads 3 are lower than the diameters of the threads 6. The voltage value is identical for networks 2 and 5 Finally, the zone out of contact is better for the network 5 than for the network 2. Figure 2 presents cuts of stencils and their respective qualities.

In Figure 2, sections of silk-screening screens 7, 8, 9, 10, 11 and 12 are shown, each passing through an opening whose flanks 13 and 14 for the screen 7, 15 and 16 for the screen 8, 17 and 18. for screen 9 and 19 and 20 for screen 10, 21 and 22 for screen 11, 23 and 24 for screen 12, they have different shapes. These forms correspond to different qualities of screen printing. The screens are considered to be made of the same material and are used for filling at the top and the deposit at the bottom, as shown in Figure 3.

The flanks 13 and 14 correspond to a good filling, since the flanks 13 and 14 are closer to each other in the lower area than in the upper zone. The flanks 15 and 16 correspond to a good demoulding since the flanks 15 and 16 are closer to each other, in the upper part than in the lower part. The flanks 17 and 18 correspond to a usual compromise in these two forms and these two qualities. The flanks approach each other at equal distance from the two surfaces of the screen 9. The flanks 19 and 20 correspond to a compromise that favors demolding as they approach each other with a smaller distance than the upper face than the lower face. of the screen 10. The four forms presented above correspond to the chemical realization of the cuts. * ~ The flanks 21 and 22 correspond to an ideal shape.

They are parallel to each other and perpendicular to the screen 11. 5 The flanks 23 and 24 correspond to the shape obtained by laser cutting. Their forms are very similar to those of the flanks 21 and 22, however, they are rough. Silkscreen uses as a support, a metal or polyester fabric. A mask made with the help of a film \ 0 photosensitive to ultraviolet light, allows the realization of stencils. The polyester fabric allows a certain elasticity, which authorizes an area out of contact that can go up to 3 or 4 millimeters without distorting the image. The out-of-contact zone favors the demolding, since the lateral surfaces in contact decrease. This zone out of contact is very important and since it > it allows the detachment of the way to be deposited, from the hole of the fabric, not obstructed during the step of the scraper. The greater the tension force of the fabric, the better the detachment of the fabric and the better the deposit will be. In the case of a polyester fabric, the tension may be greater the greater the number of threads per unit length. Now, a greater number of threads allows a lower yield (the yield being the ratio between the free surface and the total surface of the mesh). The opening percentage being lower, the pasty and / or viscous product will be more difficult to pass and it becomes impossible for very small openings. The metallic mesh, generally made of stainless steel mesh, due to its superior strength, allows to offer an opening percentage higher than polyester (70% maximum). Thus, the size of the deposits can be reduced. On the other hand, the zone out of contact, that is, the possible zone, without contact, will be inferior to the polyester and the detachment may be more delicate, which creates the risk of dragging the product into the screen (Note: The strong tension is near the breaking point). When the size of the required deposits must be even smaller, it is necessary to resort to a metallic stencil. In this case, the opening percentage is 100%. Now, the biggest defect of the metallic stencil is not to admit practically any zone without contact. The metal is not extensible, it is rigid and its permissible bending angle is very small. In practice, a non-contact pseudo-zone is achieved by suspending the metallic screen on a screen of polyester threads. With the metal the contact zone is very wide.

With the synthetic material, made in the form of a sheet according to the invention, which is flexible and extensible, and with the permissible bending angle of large size, a contact surface of little width is obtained. Here is a major problem, as it often happens, for small openings that the adhesive forces of the product to be deposited on the side face of the hole are greater than the adhesive forces of the product on the support. In this case, the deposit can not be made and the product is dragged over the stencil. Figure 3 presents a view of a deposit of a thick layer. Figure 3 shows a stencil 25 carrying threads 26 and a material 27 on which a doctor blade 28 which applies a solder paste 29 or a glue or any other viscous material in the holes 30, 31 and 32, is supported. that the solder paste passes the holes and is deposited in the form of dots 34 on a printed circuit 33, when the stencil 25 moves away from a printed circuit 33. The stencil 25 is made according to the methods known to the expert. It carries threads 26 that ensure solidity and a material 27 that ensures the impermeability of the stencil 25. The squeegee 28 is of known type. It is of a hardness adapted to prevent the paste passing between it and the stencil 25. The solder paste 29 is a viscous paste that carries various components, between / which exist conductive materials of electricity. The material is expanded in the holes 30, 31 and 32. In Figure 3, the hole 31 is much smaller than the hole 30. The hole 30 is empty and the orifice 32 is in the process of being filled. The screen is stretched upwards, to move away from the printed circuit 33 before and after the step of the squeegee 28. It supports the solder paste at the same time * t? 0 29 on the stencil 25 and the stencil itself 25 on the printed circuit 33. When the squeegee moves from the right in Figure 3 to the left. The solder paste enters the holes 30, 32 and then 31 and comes out of these holes when the stencil of the printed circuit 33 moves away. Then the solder paste 29 constitutes points 34 on the circuit .A printed 33. It is easily understood in this Figure why the shape of the flanks of the holes, 30, 31 and 32 made in the stencils correspond to the qualities presented in Figure 2. It is also understood that the qualities of the stencil 25 depend on the threads 26 possibly inserted in the material 27, the elasticity of the stencil 25, its thickness and the way it makes its holes. In accordance with the present invention, the stencil or the Screen screen 25 is constituted by a solid sheet of synthetic material, extensible and flexible, such as polyester or plastic derivatives or similar materials, preferably configured by mechanical cutting to make the circular holes. According to the invention, the material used for the realization of the stencil is apt to undergo a local conformation by means of plastic deformation for example, to allow the passage of over-thicknesses. The present invention also relates to the stencil itself 25, as the deposit intended to perform the process. To remedy the problems encountered in the screen screen of polyester or metallic fabric and with metallic screen, the present invention proposes to use a polyester or derivative screen screen in the form of a solid sheet. This solid sheet of polyester is drilled mechanically or thermally at the desired sites. The polyester fabric, since it is a solid type, accepts tensile forces superior to fabrics with metallic threads and at least equal to metallic stencils. In Figure 4 a stencil 42 is shown carrying a hole 35, whose flanks 36 and 37 constitute a classic compromise in the electronics industry and a stencil 38 according to the invention which carries a hole 39, the orifice 39 of which flanks 40 and 41 are made of mechanical means. Stencil 42 is metallic. It has an orifice 35 whose flanks 36 and 37 were presented in Figure 2 as the compromise, that is the usual eclectic solution in the electronics industry. Stencil 42 badly accepts areas without contact, has a very limited angle of folding because of its base material and has high friction coefficient. The stencil 38 according to the present invention is constituted by a solid sheet of polyester, made "0 by mechanical trimming. It has a hole 39, whose flanks 40 and 41 are made by drilling, and therefore, have an almost ideal shape, as shown in Figure 2. Stencil 38 accepts areas without high contact, has a very high angle of folding and a reduced coefficient of 15 rubs. The precision of the clipping shape is very high. "" 'Figure 5 presents a screen made according to the present invention. In Figure 5 the embodiment of a deposit on a substrate surface 33 through a stencil according to the invention is represented by a squeegee 28. The printed circuit that will receive the deposits of the viscous or pasty and / or sticky products, presents an enhancement, that is roughness with different thicknesses. These highlights are due to the presence of runways and reception beaches. The rule that must be respected so that there is a transfer of the product depositable in the substrate is that there is contact between the stencil and the substrate in place precise where the doctor blade exerts a linear pressure and in front of an opening. If there is no contact in front of the opening, the product will be guided through the hole, but will be received randomly with expansions and burrs. ^ 0 In the case of the use of a stencil in the form of a sheet according to the invention (FIG. 5), the criteria of flexibility and extensibility of the stencil associated with reduced values of the admissible bending radius, give rise to a deformation of the screen. it allows you to enter into 15 contact with the substrate, including the lowest points. Different manufacturing processes can be foreseen, however, it turns out that the perforation of the circular holes was the most adapted for the polyester stencil made of a sheet according to the invention.If the cutting parameters are well adapted, the edge is clear and clean with possibilities of drilling diameters that can go up to 0.001 mm The great advantage of the mechanical manufacture by means of 25 bits resides in the fact that for a same perforation diameter, it is the same bit that works, it does not matter - what is the number of holes or holes of the diameter in question that must be practiced The bit, that is, the bit, is a tool with a constant diameter and profile and with a cutting speed calculated as a constant value. with constant thickness and character, all this leads to constant hole diameters with an identical surface state in all holes of the same hole diameter The holes are smooth with a roughness of the order of 0.001 μ (by 0.1 μ, with laser cutting). The constancy of these parameters applied to the stencil in sheet form according to the invention, as well as the fact that the holes made for the same diameter are rigorously identical, allows to make deposits rigorously similar. The modification of the surface condition of the • - • * perforations allow different results to be obtained, particularly in terms of the dosing of the products deposited and the height of the points made in relation to with the diameter of the perforations. In this Figure 9, to facilitate its understanding, the stencil 25 has been represented on the one hand, applied on the substrate 33 (printed circuit) and on the other hand, the elevation course to represent the elevation of the queue for stenciling and the action it can take on the formation of tail points. Figure 6 shows a plan view and section, as an example of depositing tail points of different heights to fix different components in the circuit. Figure 7 shows an example for the constitution of physical barriers by tail points between zones where there is a risk of bridging during the passage to the welding wave. In Figure 8 the embodiment is represented by points of continuous lines and solid surfaces. The material that sticks to the side walls of the holes with the same diameter is strictly identical to one another. The solid sheet of polyester has no insert, nor any particular formation. Its thickness is constant and it is homogeneous. In addition, the polyester used is transparent. The reference of the respective positions of the stencil and of the printed circuit, turns out to be therefore better. The deposited height is a function of the diameter of the hole, the viscosity of the product, its density, the thickness of the stencil and the forces that oppose runoff (roughness). In the case of polyester, with constant roughness and the other parameters also constant, the result will also be constant, that is, for a same hole diameter, we will always have the same deposit height. With a metallic stencil and with variable roughness, deposits are not constant. Viscosity is the factor that most influences the height of the deposit. The lower the viscosity the more, the deposited height will approach the thickness of the stencil, all this regardless of the diameter of the hole. For high viscosities (eg, with deposit of adhesives), the deposited height is a function of the diameter and thickness of the stencil. For very small diameters (from 200 to 400 μ), the deposited height is well below the stencil thickness. The hole serves as a reservoir and is recharged with each step of the doctor blade with a quantity of viscous product equivalent to that which was deposited in the circuit. The adherence of the glue on the flanks of the hole generates a part with the stencil and only leaves another part on the substrate. The part rearrastrada by the stencil is controlled perfectly well and is of repetitive character due to the constancy of the roughness of the orifice. For the same thickness and for the same perforation diameter or dimension (from 800 to 1200 μ), the partial re-drag of the very viscous glue, during the separation, causes the systematic realization of a dome whose height can go up to 1.8 times the diel thickness stenciled. For diameters greater than 2000 μ and for the same thickness, the deposited heights are identical to the stencil thickness. If you want to deposit higher heights, you have to choose a thicker stencil and select the appropriate perforation diameter, knowing that for the smallest diameters, the deposited height will be identical whatever the thickness of the stencil. The properties of the invention allow cohabitation / - the one in juxtaposed condition (there is no shape limit) of the very high tail lines and the very low tail lines. The ratio of 1 to 20 is possible. It is possible to glue from side to side, that is in juxtaposition, microcomponents and thick pavements. Its considerable advantage over metallic stenciling is that, in spite of its equivalent tension, stenciling performed according to the present invention, it also admits an elasticity that allows having a non-contact zone during the deposit, while ensuring a contact intimate with substrate. With an opening percentage equivalent to 100%, the possible deposit size becomes even smaller. For deposits of a solder cream, it is preferable to deposit circular shapes even in reception areas of various shapes, such as a square or a rectangle. The circle will be deposited better since it is the largest 17 surface for the smallest perimeter, maximum adhesion force in the support for a drag force by means of a minimum stencil. The deposition of glue micro-points or cream of solder through a use of the device that is the object of the present invention, achieves limiting diameters of approximately 100 μ with a limit height of 50 μ. Other advantages are added to these qualities of the polyester stencil in the form of a perforated solid sheet, ie: - the sale price is divided at least by 3; - the means to apply the system for manufacturing are less than for the metallic stencil; - the polyester is inalterable to acids and solvents; 15 - the life span is longer than that of the metallic stencil. - the polyester stencil may undergo, if necessary, a permanent practical deformation to avoid certain areas of the circuit, if necessary.

Claims (17)

1. CLAIMS: 1. A stencil (25), (38) for depositing and dosing more or less thick layers based on dots or in the form of dots of a viscous product on a substrate, this stencil consisting of a solid sheet and homogeneous made of synthetic material, and provided with holes that are made by perforations, characterized in that: the thickness of the sheet is determined in function of the greater height of deposit that is made in the substrate. - because the sheet has different perforation diameters depending on the height of the different deposits that must be made, said diameters being also conditioned by the thickness of the sheet, and in that the perforations constitute a deposit that is loaded in each step made by a doctor blade with a quantity of product of which all or part will be deposited on the substrate in a regular way by close contact between the stencil and the substrate at the place where the doctor blade exerts a linear pressure and faces the opening of the perforations , which allows dosing the quantities of the deposited product and controls the height of the deposits, the doses of the deposited product being different here, as well as the deposit heights obtained by one step of the doctor blade.
2. 2. The stencil according to claim 1, characterized in that: the smaller perforation diameter of the stencil can go to have a dimension smaller than the thickness of the stencil sheet.
3. 3. The stencil according to claim 1, characterized in that each of the perforations, whatever their size, has a constant diameter over the entire thickness of the sheet.
4. 4. The stencil according to claim 1 and claim 3, characterized in that the holes of "7" or perforation made for any of the different diameters, are strictly identical for the same diameter, which allows to make rigorously similar deposits
5. 5. The stencil according to claim 3, characterized in that the walls of the perforations are 15 relatively smooth with a surface roughness of the order of 0.001 miera.
6. 6. The stencil according to claim 1, , < ** - characterized in that the flanks of the perforations are parallel to each other., 7.
7. The process for depositing and dosing viscous products in more or less thick layers based on dots or in the form of dots on a substrate, this method comprising placing a flat stencil above the substrate and applying the viscous product 25 on the substrate through stencil perforations, 20 performed by the action of a doctor blade that exerts a linear pressure on the screen plan perpendicularly to the stencil and to the substrate, in the opposite direction to the substrate, this linear pressure being enough to deform the stencil and to put it in contact with the substrate at the exact point of the linear pressure, in which the perforations of the stencil correspond to the deposit that is made on the substrate, characterized in that the stencil below is constituted by a solid and extensible homogeneous sheet made of an elastic synthetic material that has a high angle of folding with perforations of transfer whose flanks are parallel to each other and perpendicular to the stencil, and in which the tension is enough to create a zone without contact between the stencil and the substrate on the side opposite the squeegee and because the amount of viscous product deposited at each point and the height of the deposited point are determined according to the of the stencil sheet and the corresponding transfer perforation diameter, so that each of the deposits emerging from the perforation, which have the same diameter and the same surface roughness, will have the same height.
8. The method according to claim 7, characterized in that the stencil is provided with perforations of at least two different diameters to make deposits of different heights on the substrate.
9. 9. The process according to claims 7 and 8, characterized in that the viscous product is a glue or solder paste. The method according to any of claims 7, 8 or 9, characterized in that the perforations are circular. The method according to any of claims 7, 8, 9 and 10, characterized in that the stencil sheet is made of polyester. ** "0, 12. The method according to any of claims 7, 8, 9, 10 and 11, characterized in that the stencil perforations are relatively smooth and have a surface roughness of the order of 0.001 mire. according to any of claims 7 to 12, characterized in that the perforations of the stencil are made by means of drills 14. The method according to any of claims 7 to 13, characterized in that the perforations are performed with laser. of claims 7 to 14, characterized in that the thickness of the stencil sheet is chosen in such a way that a perforation diameter of 200 to 400 microns achieves a deposit height less than the stencil thickness and a perforation diameter 5 greater than 2000 microns makes a deposit height clearly equal to the thickness of the stencil sheet. (/ 16. The procedure for the manufacture of screens of screen printing from a solid and homogeneous sheet, made of synthetic material, equipped with holes made by 5 perforations, characterized in that it consists in determining the thickness of the sheet in function of the greater height of deposit that must be made in the substrate, and in making perforations with different diameters, depending on the height of the different deposits that must be made, .0 The diameters mentioned by the thickness of the sheet are also conditioned. 17. The method according to claim 16, characterized in that it consists in using a mechanical equipment to effect the cuts of the sheet made of synthetic material.