JP4196126B2 - Circuit board manufacturing method - Google Patents

Description

  The present invention relates to a method for manufacturing a circuit board in which circuit patterns of a plurality of layers of a surface layer of a double-sided circuit board or a multilayer circuit board are conductively connected.

  In recent years, with the downsizing and increasing the density of electronic devices, there has been a strong demand for multilayer circuit boards not only for industrial use but also for consumer use.

  In such a circuit board, it is indispensable to newly develop a connection method for connecting inner via holes between circuit patterns of a plurality of layers and a structure having high reliability. A method of manufacturing a high-density circuit board having a configuration has been proposed. A method for manufacturing this circuit board will be described below.

  A conventional method for manufacturing a double-sided circuit board and a multilayer circuit board, here, a four-layer circuit board, will be described with reference to FIGS.

  First, a method for manufacturing a double-sided circuit board serving as a base of a multilayer circuit board will be described.

  3A to 3G are process sectional views of a conventional method for manufacturing a double-sided circuit board.

  Reference numeral 1 denotes a prepreg sheet. For example, a base material made of a composite material in which a non-woven aromatic polyamide fiber having a thickness t1 (150 μm) and a compressibility of about 35% is impregnated with a thermosetting epoxy resin is used. For the prepreg sheet 1, a porous material having pores is selected in order to obtain compressibility.

  2a and 2b are releasable films in which a Si-type release agent is applied on one side, and for example, polyethylene terephthalate is used. Reference numeral 3 denotes a through-hole, which is filled with a conductive paste 4 that is electrically connected to metal foils 5 a and 5 b such as Cu to be attached to both surfaces of the prepreg sheet 1.

  First, as shown in FIG. 3 (b), a through hole 3 is applied to a predetermined portion of the prepreg sheet 1 {FIG. 3 (a)} having the release films 2a and 2b bonded to both sides, as shown in FIG. 3 (b). Is formed. Next, as shown in FIG. 3C, the conductive paste 4 is filled into the through holes 3 by using a printing method or the like.

  Next, as shown in FIG. 3 (d), the release films 2 a and 2 b are peeled from both surfaces of the prepreg sheet 1.

  And as shown in FIG.3 (e), metal foil 5a, 5b is piled up on both surfaces of the prepreg sheet 1. FIG. In this state, the thickness of the prepreg sheet 1 is compressed (t2 = about 100 μm) and the prepreg sheet 1 and the metal foils 5a and 5b are heated and pressed by a hot press as shown in FIG. 3 (f). Are adhered, and the metal foils 5 on both sides are electrically connected by the conductive paste 4 filled in the through holes 3 provided at predetermined positions.

  Then, as shown in FIG. 3G, the metal foils 5a and 5b on both sides are selectively etched to form circuit patterns 6a and 6b, thereby obtaining a double-sided circuit board.

  4A to 4D are process cross-sectional views showing a conventional method for manufacturing a multilayer substrate, and show a four-layer substrate as an example.

  First, as shown in FIG. 4 (a), the double-sided circuit board 10 having the circuit patterns 6a and 6b manufactured according to FIGS. 3 (a) to 3 (g) and the double-sided circuit board 10 manufactured according to FIGS. 3 (a) to 3 (d). Pre-preg sheets 1a and 1b in which the through holes 3 are filled with the conductive paste 4 are prepared.

  Next, as shown in FIG. 4B, the metal foil 5b, the prepreg sheet 1b, the double-sided circuit board 10, the prepreg sheet 1a, and the metal foil 5a are positioned and stacked on the laminated plate in this order.

  Next, with the product placed on a laminated plate (not shown), the thickness of the prepreg sheets 1a and 1b is compressed (t2) as shown in FIG. The double-sided circuit board 10 and the metal foils 5a and 5b are bonded together, and the circuit patterns 6a and 6b are connected to the metal foils 5a and 5b by the conductive paste 4 and the inner via holes.

  And as shown in FIG.4 (d), a four-layer board | substrate is obtained by selectively etching the metal foil 5a, 5b of both surfaces, and forming the circuit patterns 6c, 6d.

  Here, a four-layer multilayer substrate has been described, but for a multilayer substrate having four or more layers, for example, a six-layer substrate, a four-layer substrate obtained by the manufacturing method is used instead of a double-sided circuit substrate, and a multilayer substrate manufacturing method { 3 (a) to 3 (g)} may be repeated.

  Although the temperature profile of the hot press is not described, in general, taking into account the number of stacked stages, quality, etc., as shown in FIG. A two-stage heating method is generally used in which the melt viscosity of the resin component of the prepreg sheet is maintained at around 130 ° C. near the lowest point to absorb temperature variations in the number of stacked sheets, and after molding, the temperature is raised to the curing temperature. Has been adopted.

  That is, emphasis is placed on the temperature at which the thermosetting resin component in the prepreg is cured (molded), that is, in the vicinity of the temperature at which the viscosity due to melting of the thermosetting resin is minimized and the temperature is maintained.

As prior art document information related to the invention of this application, for example, Patent Document 1 is known.
JP-A-6-268345

  However, in the conventional circuit board manufacturing method described above, the following problems arise when the through holes are made smaller in diameter and the through holes are made narrower in order to cope with finer circuit boards.

  In other words, the prepreg sheet as a porous material has pores for obtaining compressibility, but when the existence ratio of the pores is high, a part of the conductive paste enters the pores. This is not preferable in terms of the resistance value of the conduction hole and the insulation with the adjacent conduction hole. Therefore, although it is preferable to use a material with a low porosity, a material with a low porosity is a material with a low compressibility.

  As shown in FIG. 6A, when the prepreg sheet 1 having a compression rate of 35% is used, the conductive paste 4 is sufficiently compressed before the resin component in the prepreg sheet flows in the surface direction. There is no outflow of the conductive paste 4 from the through hole, and a stable connection resistance value is obtained.

  However, when a prepreg sheet having a low porosity and a low compression rate is used, that is, in the case of a prepreg sheet 1 having a compression rate of less than 10% as shown in FIG. The compressibility of the powder becomes smaller, and the pressure contact force between the conductive particles in the conductive paste also decreases.

  From this, when the resin component in the prepreg sheet 1 is melted and flows in the surface direction by heating and pressing, the conductive paste 4 flows out of the through holes as shown in the conductive paste flow 15, In some cases, the connection resistance value increases and the quality of the circuit board is degraded.

  In order to solve the above-described problems, the present invention provides a conductive paste having a through-hole formed in a prepreg sheet having a base material impregnated with a resin, and a conductive filler and a thermosetting resin as main components in the through-hole. The first heating temperature set to the softening point temperature of the resin in the prepreg sheet is maintained while pressing the prepreg sheet and the metal foil at least at a predetermined pressure. After heating and pressurizing for a certain time, the second heating temperature set to a temperature higher than the first heating temperature is maintained for a predetermined time while maintaining the second heating temperature, and then set to a temperature higher than the second heating temperature. A step of heating and pressurizing for a predetermined time while maintaining the third heating temperature, and the first heating temperature starts to soften the thermosetting resin component in the conductive paste and the viscosity is the lowest point. Reach High-quality circuit board by stabilizing the connection resistance of the through hole filled with conductive paste in the through hole, even when using a prepreg sheet with low compressibility, by the circuit board manufacturing method characterized by temperature Is to provide.

  The present invention is stepwise with a first heating temperature set to a relatively low temperature, then a second heating temperature higher than this, and a third heating temperature set to the curing temperature of the resin in the prepreg sheet. By increasing the temperature of the substrate and applying heat and pressure, the adhesion between the outermost layer and the interlayer can be improved. For circuit boards with conductive holes using conductive paste, the connection resistance is stabilized. A high-quality circuit board can be provided.

  The present invention also provides a prepreg sheet that is heated and pressurized at a predetermined pressure for a predetermined time while maintaining a first heating temperature set in the vicinity of the softening point of the impregnating resin constituting the prepreg sheet. The resin flow can be suppressed, and this is particularly effective when using a prepreg sheet having a low longitudinal compression ratio.

  The present invention also provides a double-sided circuit board in which metal foils are arranged on both sides of a prepreg sheet, or a multilayer in which metal foils are arranged on the outermost both sides after positioning and overlapping the prepreg sheets on both sides of a circuit board having two or more layers. It is effective for circuit boards and is heated and pressurized at a predetermined pressure for a certain time while maintaining the first heating temperature set at a temperature (range) near the softening point of the impregnating resin constituting the prepreg sheet. The metal foil or the conductive circuit on the circuit board and the prepreg sheet have the effect of enhancing the adhesion between different materials.

  In addition, the present invention is particularly effective in adopting a prepreg sheet having a conductive hole filled with a conductive paste, and only the conductive paste is pressed intensively and the metal foil is in contact with the prepreg sheet. As the resin component in the conductive paste increases and diffuses on the surface of the metal foil, the pressure contact force between the conductive particles increases, and the conductive paste due to resin melting of the prepreg sheet becomes difficult to flow out, so that the connection resistance value is stabilized. It has the action.

  The present invention employs a softening point of the thermosetting resin in the conductive paste that is lower than the softening point of the resin in the prepreg sheet, so that the resin component of the prepreg sheet has a high melt viscosity, that is, a resin. The prepreg sheet is easy to compress by making it soft but difficult to flow, and the pressure contact force between the conductive particles in the conductive paste can be increased, and the deformation of the prepreg sheet is reduced due to resin melting of the prepreg sheet. Thus, the resin flow can be reduced and the conductive paste can hardly flow out.

  In addition, at the first heating temperature, the softening of the resin in the conductive paste is promoted, and the viscosity of the conductive paste is set near the lowest point, so that the resin component in the conductive paste is easily diffused to the surface of the metal foil. Thus, the pressure contact force between the conductive particles can be increased.

  Moreover, this invention has the effect | action that the double-sided or multilayer circuit board adhesiveness as a copper clad laminated board can be improved in employ | adopting the prepreg sheet of the B stage state which has compressibility.

  In addition, the present invention can realize the mechanical strength and light weight of the circuit board by using a prepreg sheet employing an aromatic polyamide fiber nonwoven fabric as a constituent substrate, and in particular, the diameter of the through hole can be reduced. In this case, the connection resistance of the conduction hole using the conductive paste can be stabilized and a high-quality circuit board can be provided.

  In addition, the present invention can improve the mechanical physicochemical strength of a circuit board by using a prepreg sheet that employs a woven or non-woven fabric of glass fiber as a constituent base material, and in particular, compresses in a relatively longitudinal direction. Even when a prepreg sheet made of a material having a low rate is used and a through hole is provided in the prepreg sheet, the connection resistance of the conductive hole using the conductive paste can be stabilized and a high-quality circuit board can be provided. is there.

  As described above, according to the present invention, after placing metal foil on both surfaces of a compressible prepreg sheet having through holes filled with a conductive paste, the prepreg sheet is added while maintaining a relatively low temperature state. After compressing the pressure, the temperature of the prepreg sheet is melted and cured by increasing the temperature in a pressurized state to stabilize the connection resistance value between the conduction hole and the circuit pattern, thereby providing a high-quality circuit board. It can be done.

(Embodiment)
Hereinafter, a method for manufacturing a circuit board according to an embodiment of the present invention will be described.

  First, the manufacturing method of the double-sided circuit board in the embodiment of the present invention shown in FIGS. 2A to 2E is the same as the conventional one, and a multilayer circuit using the double-sided circuit board as a circuit board for an inner layer. Since the substrate manufacturing method is almost the same as the conventional method, the description thereof is omitted here.

  Therefore, the heating and pressing process in the hot press shown in FIG. 2 (f), which is a feature of the circuit board manufacturing method of the present invention, will be described in detail below.

  First, a prepreg sheet 1 is hot-pressed with a composite material in which a non-woven aromatic polyamide fiber of 250 mm square and a thickness of about 110 μm is impregnated with a thermosetting epoxy resin having a softening point of about 70 ° C. at a temperature rise of 3 ° C./min. It was later compressed to about 100 μm and used in a B stage (semi-cured) state.

  In addition, the conductive paste 4 filled in the through holes 3 is mainly composed of a conductive filler and a thermosetting epoxy resin (solvent-free type), and contains an acid anhydride type curing agent, each of which is 85% by weight. The one kneaded sufficiently with three rolls to be 12.5 wt% and 2.5 wt% was used.

  Moreover, although Cu powder with an average particle diameter of 2 μm is used as the conductive filler, powders of Au, Ag, and alloys thereof may be used.

  In particular, as the thermosetting epoxy resin (solvent-free type), the one having the lowest viscosity due to softening and melting at 70 ° C. or lower was selected.

  The softening point of the thermosetting epoxy resin (solvent-free type) contained in the conductive paste 4 is preferably selected to be lower than the softening point of the thermosetting epoxy resin impregnated in the prepreg sheet 1.

  FIG. 1 is a diagram showing a press profile in an embodiment of the present invention, which relates to a temperature and pressure profile of a hot press.

  The number of stacked sheets in the hot press apparatus was 10 sheets / step (not shown) through a mirror plate such as stainless steel having a thickness of about 1 mm. Further, the press profile shows only the press temperature, the press pressure, and the prepreg sheet temperature, and the vacuum pressure and the like are omitted for convenience of explanation.

  As shown in FIG. 1, the press profile of the present invention has a first heating temperature (a temperature corresponding to the compression zone of the conductive paste in the figure), a second heating temperature (a resin component in the prepreg sheet in the figure). And a third heating temperature (a temperature corresponding to the resin component curing zone in the prepreg sheet in the figure).

  In the temperature profile in the press profile, the first heating temperature zone was sharply raised from room temperature to 70 ° C., then held for 30 minutes, and the pressure was 5 MPa when the temperature reached 70 ° C.

  In the first heating temperature zone, the prepreg sheet temperature gradually rises, converges to a temperature slightly lower than 70 ° C., and is maintained for about 10 minutes.

  In the first heating temperature zone, the thermosetting epoxy resin (solvent-free) component in the conductive paste begins to soften and its viscosity reaches the lowest point. As a result, the conductive paste 4 is easily deformed by pressure and is slowly compressed. For this reason, the thermosetting epoxy resin (solvent-free type) is diffused from the through hole 3 to the metal foil, and at the same time, the pressure contact force between the Cu powders in the conductive paste can be increased.

  By the way, when the prepreg sheet after 30 minutes at 70 ° C. in the middle of the formation of the circuit board is taken out and the metal foil on both sides is peeled off and observed, the resin in the conductive paste is diffused in the metal foil, and the prepreg sheet It was confirmed that the film was slightly molded and the thickness was reduced.

  Here, the resin in the prepreg sheet having a softening point of about 70 ° C. at a temperature rise of 3 ° C./min is set to 70 ° C. heating, but the first heating temperature of the press profile of the present invention is the temperature of the prepreg sheet. May be set in the vicinity of the softening point of the resin, and may be set in the vicinity of the softening point of the resin by changing the heating method even at a temperature of 70 ° C or higher. Here, the temperature in the low temperature region is set to 70 ° C., but may be set according to the softening temperature of the resin component in the prepreg sheet.

  Next, in the temperature profile in the press profile, the second heating temperature zone is increased at 3 ° C./min to around 130 ° C., which is the resin component molding start temperature in the prepreg sheet, while maintaining the pressure. In order to reduce the temperature variation between them and form uniformly, the holding time was about 20 minutes.

  Furthermore, in the temperature profile in the press profile, after the temperature is increased at 3 ° C./min up to 200 ° C., which is the curing temperature of the resin in the prepreg sheet, in the third heating temperature zone and held for about 60 minutes for curing. The cooling (not shown) is used.

  The pressure profile was 5 MPa from the start of temperature rise in the conductive paste compression zone to the middle of cooling.

  When this press profile is used, the temperature of the prepreg sheet itself is about 70 ° C. of the first heating temperature. After the temperature of each prepreg sheet is converged and maintained for a certain time, the second heating is performed. After maintaining for a certain period of time while slightly converging around 130 ° C., the third heating temperature of 200 ° C. is maintained.

  The connection resistance value of the conduction holes of the double-sided circuit board {FIG. 2 (g)} and the four-layered circuit board (not shown) manufactured with the press profile of the present invention is compared with the circuit board manufactured with the conventional press profile. It improved about 20%.

  Moreover, even if it confirmed the periphery of the through-hole 3, it has confirmed externally that there is no outflow of an electrically conductive paste.

  In the embodiment, a base material made of a composite material in which a non-woven base material composed of aromatic polyamide fibers is impregnated with a thermosetting epoxy resin in a prepreg sheet is used. It may be a prepreg impregnated with a resin material mainly composed of a functional resin to form a B stage.

  Further, a prepreg obtained by impregnating a woven or non-woven fabric mainly composed of glass fiber with a resin material mainly composed of a thermosetting resin to form a B-stage may be used. In particular, a prepreg sheet having a low compressibility has the effect of the press profile of the present invention. For example, when using a prepreg with a compression ratio of less than 10%, which is impregnated with a thermosetting resin into a woven fabric mainly made of glass fiber and B-staged, the connection resistance value of the conduction hole is improved by about 30%. confirmed.

  In the embodiment, the multilayer circuit board having four layers is described as the multilayer circuit board. However, the same effect can be obtained by using a multilayer circuit board having four or more layers.

The figure which shows the press profile in embodiment of this invention Sectional drawing which shows the manufacturing method of the double-sided circuit board in embodiment of this invention Sectional drawing which shows the manufacturing method of the conventional double-sided circuit board Sectional drawing which shows the manufacturing method of the conventional multilayer circuit board of 4 layers Diagram showing conventional press profile The figure which shows the subject in the manufacturing method of the conventional circuit board

Explanation of symbols

1, 1a, 1b Prepreg sheet 2a, 2b Release film 3 Through hole 4 Conductive paste 5a, 5b Metal foil 6a, 6b, 6c, 6d Circuit pattern 10 Double-sided circuit board

Claims (2)

Forming a through hole in a prepreg sheet having a base material impregnated with a resin, and filling the through hole with a conductive paste mainly composed of a conductive filler and a thermosetting resin;
A step of stacking at least the prepreg sheet and a metal foil;
While pressurizing this at a predetermined pressure, while maintaining the first heating temperature set to the softening point temperature of the resin in the prepreg sheet, heating and pressurizing for a certain period of time, then a temperature higher than the first heating temperature Heating and pressurizing for a certain period of time while maintaining the second heating temperature set to 1, and then heating and pressurizing for a certain period of time while maintaining the third heating temperature set to a temperature higher than the second heating temperature; With
The method of manufacturing a circuit board, wherein the first heating temperature is a temperature at which the thermosetting resin component in the conductive paste starts to soften and reaches its lowest point. The second heating temperature is a resin component molding start temperature in the prepreg sheet,
The method for manufacturing a circuit board according to claim 1, wherein the third heating temperature is a curing temperature of a resin in the prepreg sheet.

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