JP4770679B2 - Method for forming conductive bump - Google Patents

Description

  The present invention relates to a method for forming a conductive bump.

  Conventionally, as a method of manufacturing a multilayer wiring plate, a conductive paste is screen-printed on a conductive layer to form a substantially conical conductive bump, and another conductive layer is stacked on top of this through an insulating layer. A method of forming electrical conduction between conductive layers on both sides of an insulating layer by pressing is known.

  The conductive bump needs to be high enough to penetrate the conductive bump in the thickness direction of the insulating layer. In addition, if the fine pitch required as a wiring board is further advanced, it may be a shape having a relatively high height relative to the bottom area while maintaining the height, that is, a shape having a so-called high aspect ratio. It has been demanded.

  However, in the current method for forming conductive bumps, since the bump formation height by the conductive paste per screen printing (squeegee process) is not sufficient, printing is generally repeated many times. Therefore, every time the conductive paste is printed, a drying step and an alignment step are required, and these steps have to be repeated until a sufficiently high conductive bump is formed. .

Therefore, it has been difficult to efficiently manufacture a high-accuracy substrate that meets the demand for fine pitch and to reduce the manufacturing cost due to the large number of man-hours.
JP-A-6-342977 JP-A-6-350258 Japanese Patent Laid-Open No. 2004-6577

  The present invention provides a method of forming a sufficiently high conductive bump with fewer steps than in the prior art.

  The method for forming a conductive bump according to the present invention includes (a) a step of filling a mold material having a recess for forming a bump shape with a conductive paste in the recess, and (b) a conductive paste filled in the recess. A step of shrinking, (c) a step of superimposing a base material on the filling in the recess, and (d) a step of separating the mold material and the base material and transferring the filling to the base material, It is characterized by including.

  Such a method for forming a conductive bump according to the present invention includes, as a preferred embodiment, one in which the step (b) is performed by heating the conductive paste filled in the recess.

  Such a method for forming a conductive bump according to the present invention includes, as a preferred embodiment, one in which the step (b) is performed by cooling the conductive paste filled in the recess.

  Such a method for forming a conductive bump according to the present invention includes, as a preferred embodiment, one in which the step (A) is a step of filling the concave portion with a conductive paste exceeding the volume in the concave portion.

  Such a method for forming a conductive bump according to the present invention includes, as a preferred embodiment, (e) after the step (d), (e) performing a step of curing the conductive paste transferred to the substrate. .

  The method for forming a conductive bump according to the present invention is different from the method of forming a conductive bump by repeatedly applying a conventional conductive paste many times and accumulating a coating layer until a desired height is reached. A sufficiently high conductive bump can be formed with a small number of steps.

  Therefore, according to the present invention, conductive bumps can be formed more efficiently and at a lower cost than in the past. The reduction in the number of processes is advantageous also in producing a highly accurate conductive bump and wiring board.

  The method for forming a conductive bump according to the present invention includes (a) a step of filling a mold material having a recess for forming a bump shape with a conductive paste in the recess, and (b) a conductive paste filled in the recess. A step of shrinking, (c) a step of superimposing a base material on the filling in the recess, and (d) a step of separating the mold material and the base material and transferring the filling to the base material, It is characterized by including.

  1A to 1D show a particularly preferable specific example of the method for forming a conductive bump according to the present invention.

  In the step (a) of the present invention, for example, as shown in FIG. 1A, a mask 3 having an opening at a position corresponding to the recess 1 is placed on a mold 2 having a recess 1 for forming a bump shape. The squeegee 4 is moved along the surface of the mask 3 while applying pressure to the cross-sectional method of the mask 3 to fill the concave portion 1 of the mold 2 having the concave portion 1 with the conductive paste 5. preferable. As the mask 3, for example, a screen mask and a metal mask are preferable. The shape, size, arrangement, and the like of the recess 1 can be determined so as to obtain desired conductive bumps and a wiring board.

  As the conductive paste, an appropriate one can be selected and used from conventionally used conductive pastes. Moreover, it can change and use suitably as needed. Particularly preferable conductive pastes in the present invention include those in which conductive fine particles are dispersed in a resin binder in an amount of 300 to 1100 parts by mass with respect to a total of 100 parts by mass of a resin component, and if necessary, further comprise a solvent. be able to. Preferred resin binders include polyester resin, phenol resin, polyimide resin, polycarbonate resin, polysulfone resin, melamine resin, epoxy resin, and the like. Preferred conductive fine particles include metal fine particles such as copper, gold, and silver. Can be mentioned.

  After filling the conductive paste with the squeegee 4 once or a plurality of times, the mask 3 is peeled from the mold material 2 before the conductive paste is solidified. Since the conductive paste has a predetermined viscosity at the time of peeling, the conductive paste 5b side of the recess 1 where a part of the conductive paste 5a existing in the opening of the mask 3 is located below is provided. As a result, as shown in FIG. 1B, a raised portion of the conductive paste is formed on the surface of the conductive paste 5b filled in the recess 1. That is, the concave portion 1 of the mold material 2 is filled with the conductive paste exceeding the volume in the concave portion 1 to form a raised portion of the conductive paste.

  The height and shape of the raised portion are the opening diameter, thickness, material, and components and properties of the conductive paste (for example, the type of resin binder, the type and amount of conductive fine particles, the viscosity), It can be controlled by the temperature, the peeling speed of the mask 3, and the like. When the formation of the raised portion is insufficient, the conductive paste 5b filled in the recess 1 in the step (b) is excessively contracted, and the transfer to the base material in the step (d) is good. Difficult to do.

  In addition, in this invention, it is preferable to provide a mold release agent to the inner wall surface in the concave part of the mold material 2 having the concave part for forming the bump shape, if necessary, before the step (A). Specific examples of preferable release agents include silicone resins, Teflon, fluorine resins, and the like. Of these, silicone resins and fluorine resins are particularly preferable. The application of the release agent is preferably performed over the entire inner wall surface of the recess 1 (that is, the side wall surface and the bottom surface inside the recess 1). The mold need not be applied to the entire inner wall surface of the recess 1 but can be applied only to a portion of the inner wall surface of the recess 1. Further, the release agent does not need to be applied uniformly over the entire inner wall surface of the recess 1, and a partially thick portion or a thin portion may exist. Here, “applying a release agent to the inner wall surface of the recess” means that the release agent is pre-mixed in the conductive paste, and the conductive paste is filled in the recess 1 and at the same time the mold 2 The aspect given to an inner wall surface is also included.

  The step (b) in the present invention is a step of shrinking the conductive paste 5b filled in the recess 1. This step (b) is performed by heating the conductive paste filled in the recess 1 (first method) and by cooling the conductive paste filled in the recess 1 (second method). ) And can be classified into two methods.

  The method (first method) performed by heating the conductive paste filled in the recess 1 mainly uses the shrinkage accompanying semi-curing of the conductive paste and evaporation of the solvent component, while the recess The method (second method) performed by cooling the conductive paste filled in 1 mainly uses an increase in viscosity and a decrease in volume due to cooling of the conductive paste.

  The heating temperature in the first method is 40 to 200 ° C, preferably 60 to 180 ° C, and the cooling temperature in the second method is -10 to 20 ° C, preferably 0 to 15 ° C. Means or apparatus for heating or cooling is optional. In the present invention, it can be preferably performed using, for example, an electric heater or an electronic cooling element utilizing the Peltier effect.

  In this step (b), the filling (conductive paste 5b) in the recess 1 shrinks, the adhesion force between the filling and the inner wall surface of the recess 1 is reduced, and in some cases, the filling and the recess. Separation from the inner wall surface of 1 occurs.

  Next, in the present invention, the step (c) of superimposing the substrate 6 on the filler in the recess 1 is performed (FIG. 1C). Since this substrate 6 functions as a conductive layer of the multilayer wiring substrate after being assembled into the multilayer wiring substrate, it is usually formed of a material having good conductivity. In the present invention, a substrate that has been used as a wiring layer material in a conventional general multilayer wiring substrate can be used as the substrate 1. As the particularly preferable substrate 6 in the present invention, a substrate made of a metal foil such as copper can be cited.

  In the present invention, next, the step (d) of separating the mold material 2 and the base material 6 and transferring the filler to the base material is performed (FIG. 1D). In the present invention, as described above, in the step (b), the adhesion strength between the filler (conductive paste 5b) and the inner wall surface of the recess 1 is reduced or peeled off, and the conductive paste 5a. Since the filler and the base material 6 are surely brought into contact with each other due to the presence of the raised portion above, and a sufficient bonding strength is obtained between the filler and the base material 6, Transfer to the substrate can be ensured.

  Although not shown, in order to make the conductive paste transferred to the base material sufficiently hard to penetrate the insulating layer (prepreg) when assembling the multilayer wiring board, A curing step can be performed. The heat treatment temperature and treatment time for curing can be determined as appropriate.

  Such protrusions transferred to the substrate 6 have sufficient hardness and height, and have a function as conductive bumps.

  In the present invention, since the conductive bump having a desired height can be formed by performing the above steps (a) to (d), the conductive bump can be formed efficiently and at low cost.

<Example 1>
50 parts by mass of phenol resin, 50 parts by mass of melamine resin, 700 parts by mass of silver powder, 10 parts by mass of extender pigment, 45 parts by mass of butyl carbitol acetate as a solvent, kneaded sufficiently with three rolls, and conductive paste A composition was prepared. This conductive paste composition had a viscosity of 250 Pa · s / 25 ° C. and a thixo index of 0.50.

  On the other hand, a mold made of SUS was prepared in which a large number of recesses having an opening diameter of 220 μm, a depth of 200 μm, and a bottom diameter of 50 μm were formed at intervals of 600 μm (center distance between the recesses). A mold release agent (silicone resin) was applied to the side wall surface and the bottom surface portion in each recess of the mold material.

  An aluminum metal mask plate having a plate thickness of 0.2 mm having holes with a diameter of 220 μm is placed on the mold material so that the positions of the holes of the metal mask and the openings of the recesses of the mold material coincide with each other. Superimposed.

  Then, the conductive paste composition prepared as described above was used in an atmosphere condition of a temperature of 20 ° C. and a humidity of 50%, using a urethane resin squeegee with a hardness of 80 °, and the holes of the metal mask and the It filled in the recessed part of the mold material.

  The mold material was heated at 120 ° C. for 1 minute, so that the conductive paste filled in the recesses of the mold material was semi-cured and contracted.

  Thereafter, a copper foil having a thickness of 18 μm was placed on the surface of the mold material after the metal mask was peeled off and pressed with a rubber roll. After the pressing, the copper foil was peeled off. As a result, the conductive paste filled in the recesses of the mold material and the conductive paste in the raised portion were transferred to obtain a copper foil on which conductive bumps were formed. Next, a main curing treatment was performed at 160 ° C. for 20 minutes. The height of the conductive bump was 180 μm. Note that the conductive paste filled in all the concave portions of the mold material was transferred without any leakage to the copper foil, and there was no concave portion where the conductive paste remained after peeling.

The figure which shows the process of the formation method of the conductive bump by this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Recess 2 Mold material 3 Mask 4 Squeegee 5, 5a, 5b Conductive paste 6 Substrate

Claims (5)

(A) A mask having an opening at a position corresponding to the recess is placed on a mold having a recess for forming a bump shape, and the conductive paste is filled into the recess of the mold through the opening of the mask. (B) a step of shrinking the conductive paste filled in the recess, and (c) removing the mask from the mold material to form a raised portion of the conductive paste , and then filling the recess. And (d) separating the mold material and the base material, and transferring the filler to the base material, thereby forming conductive bumps. Method.   The method for forming a conductive bump according to claim 1, wherein the step (b) is performed by heating the conductive paste filled in the recess.   The method for forming a conductive bump according to claim 1, wherein the step (b) is performed by cooling the conductive paste filled in the recess.   The method of forming a conductive bump according to any one of claims 1 to 3, wherein the step (a) is a step of filling the concave portion with a conductive paste exceeding the volume in the concave portion.   The method for forming a conductive bump according to claim 1, wherein after the step (d), (e) a step of curing the conductive paste transferred to the substrate is performed.

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