FR2837345A1 - Method of refilling the hollow grid of the printed circuit boards during the manufacture of IC chips, uses a mesh which rests on the substrate without any deformation, and which acts as a guide for the injection unit - Google Patents

Abstract

The method includes injection of liquid or paste product (8) along a metallic mesh screen in contact with the top plane (3) of the substrate. The screen tension is associated to the intextensibility of the metallic mesh (4) forming a non-deformable plane under the effect of the force of the transfer of the product in the zones situated in the hollow. This mesh (4) presents, an opening having a ratio greater than 50% of the injector opening, to minimise overflow of the product when the screen is lifted to separate the mask from the substrate.

Description

of the heat conductor (12).

  METHOD FOR FILLING ZONES LOCATED IN A HOLLOW AREA

SUBSTRATE

  FIELD OF APPLICATION OF THE INVENTION

  The present invention consists of a method which makes it possible to fill hollow areas on a subskat. As an example, it finds its application in electronics for the realization of printed circuits when it is a question of placing on the same level of s p arties in sail li e which generally wind of s p i ste s s conductors with s

  hollow parts which generally sell insulating inter-tracks.

DESCRIPTION OF THE PRIOR ART

  0 Generally when it is a question of filling zones located in hollow on a substrate, one proceeds to a coating of all the substrate followed by a polymerization or a drying according to the product concerned, then one proceeds to a brushing to Eliminate the undesirable excess thickness of product which has polluted the pedestals and allow it to be exclusively

  product between tracks. The coating can be done using a doctor blade or a roller.

  This process is problematic when the area to be filled is relatively large. In fact, when the area to be filled exceeds 2 mm in width, the coating element, which moreover must have a certain flexibility so as not to deposit significant thicknesses, tends to hollow out the deposit previously made. This problem is further accentuated when the hollow area is parallel to the coating device, because in this case, the latter sinks into the hollow at the risk of even clinging to the tracks during its advancement. Those skilled in the art also know the screen printing using polyester mesh screens or sole, but it is only applicable for deposits on relatively flat substrates and thin thickness which the wind valleys less than 30 p, the thickness being given by the thickness of the emulsion, the mesh size and the wire diameter. This type of screen printing is not applicable in the present case, because it involves depositing thicknesses of large products (greater than 100 p) in areas located in a hollow so as to bring the conductive part and the same level to the same level. insulating part. However, a polyester or sole mesh is used precisely for its characteristics of extensibility in order to conform to the substrates and thus to ensure intimate contact with the latter. Metallic mesh screens, for example made of stainless steel, are also known and make it possible to obtain higher opening percentages at equivalent screen tension. In fact, there again, these wind screens used on flat substrates which must come into intimate contact over their entire surface with the mask so as to obtain a perfect seal between the mask and said substrate. A major drawback of stainless steel mesh screens is that they do not conform

  s not good at variations in height.

DESCRIPTION OF THE INVENTION

  In the present invention, it is precisely sought to exploit this drawback to play the mask a role which is to form a perfect and undeformable plane which is supported on the highest surfaces of which the emulsion of 0 masking is no longer thicker but only in the mesh and whose surface

  open is only an injection zone located opposite the hollows to be filled.

  In the present invention, the screen is no longer used to allow a volume of liquid or pasty product deposit to be perfectly controlled in thickness, but on the contrary to allow a liquid or pasty product to pass freely through the least mesh thick possible knowing that the thickness to be deposited is regulated by the thickness of the trenches or hollow to be filled. In fact, the screen plays a role here

  for guiding the transfer tool and defining the upper filling plane.

  The present invention aims to provide a solution for filling hollow areas also called slices due to their significant depth (greater than 100) on a substrate relative to an upper plane. Wile consists in affixing a screen with a metallic mesh, preferably in stainless steel, and having a percentage of opening greater than 50% and a thickness less than 150p, in contact with the upper plane and performing an injection operation at [ using a

  transfer, then separate the mask from the subskat.

  2s According to a first characteristic the mesh is metallic therefore inextensible unlike a polyester or sole mesh. This non-extensibility of the material associated with the tension of the screen prevents the sinking of the mesh in the areas located in the hollow which allows complete filling under the effect of the transfer device which can be a doctor blade or a direct injection device. . Indeed, for the kansfert of a more or less viscous product to take place through a mask, it is imperative to impart a force to the product to be transferred which has a component perpendicular to the mask. This component is called kansfer force and causes not only a passage of the product through the mask but also a support of the mask against the substrate located below. This support is favorable when screen printing a flat substrate, because it allows by plating to ensure the seal between the mask and the substrate and thus obtain well-defined deposits. Moreover, to further improve this sealing, the skilled person uses polyester mesh or sole screens so that the extensibility of the material thus allows a perfect conforming of the mask on the subskat. By conke, this extensibility becomes harmful for the filling of a hollow area because the shaping of the mask goes against the filling

total of these areas.

  lo According to another characteristic of the invention, the mesh used for the production of the mask has a percentage of opening greater than 50% so as not to re-entrain the product previously deposited in the hollow areas. The percentage of opening of a mesh is determined in the following way: Percentage of opening = (opening) 2 1 opening + ó wire - opening being the open distance between two wires of the mesh,

  - wire being the diameter of the wire constitute the mesh.

  For example, an 80 mesh mesh gives very good filling results since it has an opening percentage of 70% (ó opening = 265 and

  of wire = 5OIl, mesh thickness of lOOIl).

  The percentage of opening greater than 50% makes it possible to limit the contact surface between the mesh and the product transferred. Thus, during the separation of the mask and the substrate, the product is not reentered by the mask and therefore remains in the hollow area. A mesh thickness of less than 150p makes it possible to minimize the excess of kansfere product during the removal of the screen, [ideal being to have a volume of

s mesh as small as possible.

  According to another characteristic of the invention, the process can be made selective if the mask is closed at the places where the product should not be deposited. For example, if we do not want to pollute the upper plane of the subskat which can be constituted by conductive tracks and fill only the inter-track or sliced areas, we will use a mouth mask at the right of the tracks and skictely on the thickness mesh

and open in the areas to be filled.

  Other characteristics of the invention will appear in the description

  figures given by way of nonlimiting example.

  Figure 1 shows a sectional view of the process.

  As can be seen in figure (la) (lb) and (lc) the method according to the invention consists in affixing a mask made of a mesh (4) of stainless steel and having an opening ratio greater than 50% on a substrate (1) having recessed areas (2) relative to an upper plane (3). The mesh (4) is stretched over a frame (5) and is blocked with the aid of an emulsion (6) at the locations of the substrate which must not be polluted by the product (8). As the transfer device (7) advances in direction (S), the product is injected through the mask into the areas where the mesh is not blocked. At the end of movement, the mask is moved away from the substrate with a view to its replacement by another to be treated and thanks to the opening rate

  important in the mesh, the product () deposited in the recessed areas (2) is not re-

  driven by the mask. As shown in (lb), the 1S stainless steel mesh stretched over the frame (5) is not extensible, it is not pressed into the areas

  hollow (2) under the effect of the transfer force FT.

s

Claims (2)

claims:   1) Method for filling a liquid or pasty product (8) with hollow areas (2) on a substrate with respect to an upper plane (3) by injection through a screen with metallic meshes in contact with said upper plane ( 3) s characterized in that the tension of the screen associated with the non-extensibility of the metal mesh (4) forms a non-deformable plane under the effect of the force of transfer of the product in the areas located in the hollow. Said mesh (4) has an opening ratio greater than 50% so that it does not re-entrain the product during the separation of the mask and the substrate and a thickness of less than 150u so,   lo minimize the overshoot of the product to be transferred (8) when removing the screen.   2) Method for filling a liquid or pasty product (8) with hollow areas (2) on a substrate with respect to an upper plane (3) by injection through a screen with metallic meshes in contact with said upper plane ( 3) according to claim 1, characterized in that the mesh (4) is plugged locally and strictly on the thickness of the mesh (4) so, con to avoid areas not in front