JP2000286560A - Multilayer fluororesin substrate and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology for preventing a PTFE core material, constituting respective layers from softening, deforming and extending at manufacturing of a multilayer board using PTFE and preventing a bonding layer from softening and melting at mounting of parts. SOLUTION: In a multilayer fluororesin substrate, at least one stacked board, where a circuit pattern is formed on one face of a stacked body 101 where a prepreg formed of fiber and polytetra fluoroethylene resin or the prepreg and a polytetra fluoroethylene film are stacked. The stacked boards are stacked via a bonding layer whose melting point is 260 deg.C-290 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluororesin substrate having a multilayer structure characterized by an adhesive layer and a method for manufacturing the same.

[0002]

2. Description of the Related Art A substrate for an electronic circuit having a multilayer wiring structure is known.

[0003] In recent years, the frequency of signals handled by electronic circuits has been increasing, and accordingly, substrates for electronic circuits having good high-frequency characteristics, specifically, low dielectric constants at high frequencies and loss of high-frequency losses, have been developed. Less is needed. In addition, a substrate having a multilayer wiring structure has been demanded in response to the integration and complexity of high-frequency circuits.

As a material having good high-frequency characteristics, a fluorine resin, particularly a polytetrafluoroethylene (PTFE) material is used. When producing a multilayer substrate using a PTFE material, first, a sheet-like material called a prepreg in which a glass cloth is impregnated with a PTFE material is first obtained. Next, a required conductive pattern is formed on the surface of the core material in which the prepreg and the PTFE film are laminated and integrated to produce a laminate. Then, a plurality of the laminates are laminated via a fusion-type fluororesin film called a bonding film, and integrated by hot pressing to obtain a multilayer substrate.

In this method, the bonding film is melted by hot pressing, and a plurality of laminated boards on which conductive patterns are formed are adhered.

[0006] The bonding film must be melted at a temperature lower than that of the core material during bonding. Good fluidity during melting. Are required.

The above requirement is required to prevent the core material from softening during bonding. Are required in order for the adhesive layer to be present uniformly and to enhance the adhesion between the stacked laminates.

As a bonding film used for a multilayer fluororesin substrate satisfying the above requirements, US
There are # 6700 manufactured by N Company and 3001 manufactured by Rogers. For example, ARL
# 6700 manufactured by ON Company is composed of a copolymer of PCTFE (polychlorotrifluoroethylene) and PVDF (polyvinylidene fluoride).

[0009]

The above-mentioned commercially available bonding films have excellent fluidity at the time of melting, but have a problem that the melting temperature is as low as about 190 ° C.

At the stage when the multilayer board is actually used, components are naturally mounted by soldering. When soldering to a multilayer board at a production site, the parts are temporarily placed at predetermined positions on the multilayer board with the solder paste attached to the leads of the parts, and the multilayer board on which the parts are temporarily placed is placed in a heating furnace. This is done by throwing in and melting the solder paste.

In this soldering step, the multilayer board is exposed to an atmosphere in which the solder melts. Of course, the multilayer substrate is required to withstand this temperature atmosphere.

According to the soldering heat test specified in JIS C-6481, a substrate to be tested is immersed in a solder bath set at a temperature of 260 ° C. for a predetermined time. In the case of a multi-layer substrate, it is required that the substrate does not undergo swelling, peeling, peeling, or the like during this test.

[0013] Also, at the time of actual mounting of components (at the time of mounting components by soldering), the substrate is kept at 240 ° C to 260 ° C.
Heated to a temperature of Therefore, a multilayer substrate is required to withstand this temperature.

As described above, the conventional bonding film used for the laminated fluororesin substrate has a melting temperature of about 190 ° C. Therefore, there is a problem in the reliability of the multilayer board when mounting the components according to the above-described soldering process.

For example, when a bonding film having a melting point of about 190 ° C. is used, an adhesive layer formed by melting the above-mentioned bonding film material exists between the multilayered laminated plates. The adhesive layer is softened or melted by heating during the soldering process.

Actually, since the entire adhesive layer does not necessarily rise to the heating temperature, it is unlikely that the adhesive layer is completely melted by the above-mentioned heating (depending on the heating time, the dimensions of the substrate and the layer structure). I can't say for sure, though). However, softening cannot be avoided.

In the case of a multi-layer substrate, there is a great demand for positioning of a laminated plate constituting each layer in order to form wirings in multiple layers. That is, it is necessary to accurately align the positions of the respective layers in order to form a contact from the conductive pattern present on the vertically separated laminated board to the component or to connect the wiring between the vertically separated laminated boards. .

When the above-described softening (in the worst case, melting) of the adhesive layer occurs, the position of the laminated plate constituting each layer is slightly shifted. At present, the required alignment accuracy is the severest and is about 100 μm. However, when the adhesive layer is softened, such a positional shift easily occurs.

The required positioning accuracy is expected to become even more severe in the future. Therefore, it is required that the softening of the adhesive layer in the above-mentioned soldering step be as small as possible.

An object of the present invention is to solve the above-mentioned problems in a multilayer substrate using PTFE.

[0021]

According to the study of the present inventors, in order to solve the above-mentioned problems, the material constituting the adhesive layer for bonding the laminates using PTFE includes:
It has been found that it is necessary to satisfy the following requirements. The melting point must be higher than the approximate heating temperature of 260 ° C for soldering. The hot pressing temperature required for the bonding step is 290 ° C. or less. Good adhesion of PTFE. Sufficient fluidity at the time of melting to function as an adhesive layer. Those that do not degrade the high-frequency characteristics of the multilayer substrate.

That is, the present invention relates to a laminated board having a circuit pattern formed on at least one surface of a prepreg comprising a fiber and a polytetrafluoroethylene resin, or a laminate obtained by laminating the prepreg and a polytetrafluoroethylene film. Wherein the laminate has a melting point higher than 260 ° C. and 2
A multilayer fluororesin substrate characterized by being laminated via an adhesive layer having a temperature of 90 ° C. or lower.

The present invention also relates to a laminate having a circuit pattern formed on one or both sides of a prepreg comprising a fiber and a polytetrafluoroethylene resin or a laminate obtained by laminating the prepreg and a polytetrafluoroethylene film. A first step of forming, and a second step of bonding a laminate including at least one of the laminates by a hot press method, wherein in the second step, the laminate has a melting point of 2
A method for producing a multilayer fluororesin substrate, characterized in that pressure is applied at a heating temperature higher than 260 ° C. and lower than 290 ° C. using an adhesive having a temperature higher than 60 ° C. and lower than 290 ° C.

In the above, the adhesive forming the adhesive layer is:
Tetrafluoroethylene / ethylene copolymer (E / TFE) is preferred. E / TFE has a melting point of 270 ° C. and can sufficiently withstand the soldering temperature at the time of mounting the aforementioned components. Incidentally, the monomer ratio between tetrafluoroethylene and ethylene is not particularly limited.

When E / TFE is used as the adhesive layer,
Since its melting point is 270 ° C, the temperature during hot pressing is
The temperature can be lower than the melting point of PTFE, which is 327 ° C (generally, hot pressing is performed at a temperature of 280 ° C to 290 ° C). During the hot pressing, the PTFE material constituting the laminate may soften or melt. Can be prevented.

E / TFE is excellent in fluidity at the time of melting and also excellent in adhesion to PTFE, so that it can function effectively as an adhesive layer. Further, they have the characteristics of high electric resistance and low dielectric constant.

It is important that the melting temperature of E / TFE is 270 ° C. Although the melting point of PTFE is 327 ° C., it partially begins to soften at a temperature lower than that during hot pressing.

In the present invention, the melting temperature of E / TFE is 2
Since the temperature is 70 ° C., the temperature at the time of hot pressing for bonding the laminated boards constituting the respective layers can be performed at 280 ° C. to 290 ° C.

The reason why the hot pressing is performed at a temperature slightly higher than the melting point of E / TFE is that the temperature of the adhesive layer is lower than the temperature of the hot press because the adhesive layer is between the laminated plates. This is because the melting point temperature or higher is set.

Generally, the temperature at the time of the hot pressing needs to be higher by 10 ° C. to 20 ° C. than the melting point of the material constituting the adhesive layer (E / TFE or FEP in the present invention).

Therefore, when the present invention is adopted, the hot pressing temperature for bonding each laminated board to the multilayer is 280 ° C.
２290 ° C.

On the other hand, in order to prevent a laminate made of PTFE as a main constituent material from being deformed or expanded by hot pressing at the time of laminating and bonding, the temperature at the time of hot pressing should be 300 ° C.
It is necessary to set the temperature to not more than ℃, preferably not more than 290 ℃.

Therefore, while having heat resistance at a temperature required for soldering (melting point higher than 260 ° C.),
Further, as a material that can function as an adhesive layer by hot pressing at a temperature of 290 ° C. or less, a material having a melting point of 26
It is extremely important to select E / TFE, a material that is higher than 0 ° C. and equal to or lower than 290 ° C.

As an adhesive satisfying the same requirements,
A tetrafluoroethylene-hexafluoropropylene copolymer (FEP) having a melting point of 275 ° C. can be used.

The structure of the prepreg is obtained by impregnating an inorganic fiber cloth such as a glass cloth with a polytetrafluoroethylene resin, dispersing an inorganic fiber such as a glass fiber in a polytetrafluoroethylene resin, or combining these. Can be adopted. Note that organic fibers such as aramid fibers can be used instead of or in addition to the inorganic fibers. For example, as the prepreg, a non-woven fabric of aramid fiber impregnated with polytetrafluoroethylene resin, or a non-woven fabric of allied fiber dispersed in polytetrafluoroethylene resin can be used.

[0036]

[Function] The melting point is 327 as a laminated plate to be laminated in multiple layers.
By using E / TFE having a melting point of 270 ° C. or FEP having a melting point of 275 ° C. as an adhesive layer for bonding the respective laminates using PTFE at a temperature of 270 ° C., the soldering temperature (at 260 ° C. ) Can be obtained, and the hot pressing temperature at the time of bonding can be 290 ° C. or lower, which is a temperature at which the PTFE material does not deform or expand.

[0037]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a process for obtaining a multilayer substrate using the present invention.

First, a prepreg containing a predetermined amount of a fluororesin is obtained by repeating a process of impregnating a glass cloth with a PTFE dispersion and further firing, and a PTFE film is laminated thereon, and furthermore, a thickness is formed on both sides thereof. 18
The copper foils 102 and 103 of μm are stacked and heated and pressed by a vacuum hot press.

Thus, the laminate 101, the copper foils 102, 1
A copper-clad laminate 104 of No. 03 having a thickness of 200 μm is obtained (FIG. 1A). In addition, as the laminated body 101, a multi-layered structure of a plurality of prepregs via a PTFE film may be used. Further, a copper foil may be directly adhered to the surface of the prepreg.

The dielectric constant and thickness of the copper-clad laminate 104 are adjusted by changing the number of times of impregnation of the glass cloth with PTFE, the thickness of the PTFE film, and the configuration pattern at the time of lamination.

After obtaining the state shown in FIG.
And 103 are formed. This pattern processing is performed by drilling using an NC machine, surface treatment (defluorination treatment) on the inner wall surface of the through hole, copper plating, and etching.

FIG. 1C shows a state in which a pattern 105 has been formed on the copper clad laminate 104 (a partial cross section after the pattern has been formed). This state is referred to as a core material 115.

In FIG. 1 (C), the copper plating pattern 1
08, and a surface treatment layer 109 is further formed. The surface treatment layer 109 is obtained by forming a micro-rough surface for improving adhesion to a bonding film described later when a multilayer substrate is formed later.

By the through holes 107 shown in FIG. 1C, contacts of the circuit pattern 105 formed on the front and back surfaces of the laminated copper clad board 104 are formed. Reference numeral 106 denotes a conductive pattern extending from the through hole.

Next, as shown in FIG.
A copper clad laminate indicated at 20 is prepared. Figure 1 shows the fabrication process
What is necessary is just to perform according to the manufacturing process shown to (A)-(B).

For example, the single-sided board 10 shown in FIG. 1C has the same structure as the copper-clad laminate 104, and one side is etched to lose the copper foil, and the copper foil 111 is provided only on one side of the laminate 112. It has a stuck structure.

After the single-sided plates 10 and 20 are obtained, a core material 115 having a through hole shown in FIG. 1B is sandwiched between the two plates via bonding films 113 and 114.

Here, as the bonding films 113 and 114, a film-shaped E / TFE having a thickness of 50 μm is used.

In this step, the single-sided plate 10 and the core material 11
5. Positioning of the single-sided plate 20 is important. After obtaining the laminated state, hot pressing is performed at 280 ° C. and a pressure of 12 kg / cm 2. Thus, a multilayer substrate in which circuit patterns are stacked in four layers as shown in FIG. 1C is obtained. Here, four layers means
This means that four conductive pattern layers are formed.

Next, through holes 117 are formed in the obtained four-layered multilayer substrate. The formation of through holes
First, an NC process is performed, and then a copper plating layer 118 is formed. The copper plating layer 118 is also formed inside the through hole 117. Then, patterning is performed, and further, solder plating 119 is performed. Portions where solder plating is not desired are covered with a resist 120 (FIG. 1D).

In this way, a multilayer substrate in which circuit patterns are laminated in four layers as shown in FIG. 1D is obtained.

An arbitrary multilayer structure can be obtained by appropriately combining the steps described above. Further, a required through-hole structure can be manufactured. Also,
For example, as the single-sided boards 10 and 20, those having circuit patterns formed on both sides may be employed, or a structure in which a copper-clad laminate or a single-sided board is further laminated in addition to the structure shown in FIG. it can. In addition, a structure in which a core material that does not form a copper foil is sandwiched in order to increase the thickness of the multilayer substrate may be employed.

Here, an example in which core materials having the same thickness are laminated as the laminated plates to be laminated has been described, but the thickness may be changed for each layer.

Further, a structure in which a through hole 107 is not formed may be adopted.

The present invention can also be used when a laminate made of PTFE and a substrate made of another material (for example, a glass epoxy substrate) are bonded.

Further, the adhesive structure of the present invention may not be employed for all the adhesive layers of the laminated structure, but may be employed for a part thereof. Further, the dielectric constant of the core material may be different for each layer.

[0057]

According to the present invention, each layer is formed at the time of manufacturing a multilayer substrate using PTFE.
It is possible to provide a technique in which the PTFE core material is not softened and deformed or elongated, and furthermore, the softening or melting of the adhesive layer does not occur when mounting the component.

[Brief description of the drawings]

FIG. 1 is a view showing a process for manufacturing a multilayer fluororesin substrate using the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Single-sided board 20 Single-sided board 101 Laminated body 102 Copper foil 103 Copper foil 104 Copper-clad laminated board 105 Copper foil pattern 106 Copper foil pattern 107 Through hole 108 Copper plating layer 109 Surface treatment layer 111 Copper foil pattern 112 Laminated body 113 E / TFE Bonding film 114 made of E / TFE 115 Core material 117 Through hole 118 Copper plating layer 119 Solder plating layer 120 Resist layer

Claims (4)

[Claims] 1. A prepreg comprising a fiber and a polytetrafluoroethylene resin or a laminate obtained by laminating the prepreg and a polytetrafluoroethylene film on at least one side of a laminate having a circuit pattern formed on at least one surface thereof. A multilayer fluororesin substrate, wherein the laminate is laminated via an adhesive layer having a melting point higher than 260 ° C and 290 ° C or lower. 2. The multi-layer fluororesin substrate according to claim 1, wherein the adhesive layer is made of a tetrafluoroethylene / ethylene copolymer or a tetrafluoroethylene / hexafluoropropylene copolymer. 3. A first method for forming a laminate in which a circuit pattern is formed on one or both sides of a prepreg comprising a fiber and a polytetrafluoroethylene resin or a laminate obtained by laminating the prepreg and a polytetrafluoroethylene film.
And a second step of bonding a laminate including at least one of the laminates by a hot press method. In the second step, the laminate has a melting point of 260.
2 ° C using an adhesive that is higher than
A method for producing a multi-layered fluororesin substrate, comprising applying pressure at a heating temperature higher than 60 ° C. and lower than 290 ° C. 4. The method according to claim 3, wherein a tetrafluoroethylene / ethylene copolymer or a tetrafluoroethylene / hexafluoropropylene copolymer is used as the adhesive.