JP5480490B2 - Adhesive film and flexible metal-clad laminate - Google Patents

Description

  The present invention relates to an adhesive film and a flexible metal-clad laminate that is obtained by laminating a metal foil to the adhesive film, exhibits stable metal foil peeling strength, and has excellent hygroscopic solder resistance.

  2. Description of the Related Art In recent years, electronic devices have been rapidly improved in performance, function, and size, and accordingly, there is an increasing demand for downsizing and weight reduction of electronic components used in electronic devices. In response to the above requirements, semiconductor device packaging methods and wiring boards on which they are mounted are required to have higher density, higher functionality, and higher performance.

  A flexible printed wiring board (hereinafter also referred to as FPC) generally uses a thin insulating film having flexibility as a substrate (base film), and a metal foil is heated and pressure-bonded to the surface of the substrate via various adhesive materials. Thus, a circuit pattern is formed on the metal-clad laminate bonded together, and a cover layer is applied to the surface. In a flexible printed wiring board (three-layer FPC) composed of three layers of an insulating film, an adhesive layer, and a metal foil, a polyimide film or the like has been widely used as an insulating film. This is because polyimide has excellent heat resistance and electrical characteristics. Moreover, as the adhesive layer, a thermosetting adhesive such as epoxy resin or acrylic resin is generally used.

  However, in order to obtain a high-density, high-function, and high-performance FPC as described above, it is necessary to improve the performance of the above-mentioned insulating adhesive and insulating film used as the material and use them. It is necessary. Specifically, the adhesive layer and the like are required to have high heat resistance and mechanical strength, and to be excellent in workability, adhesion, low moisture absorption, electrical characteristics, and dimensional stability.

  On the other hand, thermosetting resins such as epoxy resins and acrylic resins that have been conventionally used as adhesive layers are excellent in low-temperature workability because they can be bonded at a relatively low temperature, and also from an economical viewpoint. However, at present, for example, other characteristics typified by heat resistance are insufficient.

  In order to solve the above problem, a two-layer FPC using a polyimide material for an adhesive layer has been proposed (see, for example, Patent Document 1). In addition, although it can be said that the FPC obtained by the method using a polyimide material for the adhesive layer is strictly three layers, the two polyimide layers are regarded as a single body to form a two-layer FPC. This two-layer FPC is superior in heat resistance, electrical characteristics, and dimensional stability compared to a three-layer FPC using an epoxy resin or an acrylic resin as an adhesive layer, and has attracted attention as a material that can meet the required characteristics in the future. ing.

  On the other hand, a drawback in using a polyimide material is a high water absorption rate based on the properties of polyimide. This is a problem that also applies to a two-layer FPC. When the water absorption rate of the FPC is high, it may adversely affect the mounting of components using solder. Specifically, moisture taken into the material from the atmosphere is suddenly released out of the system by heating at the time of component mounting, resulting in swelling and whitening of the FPC, and between the materials in the FPC There may be problems with adhesion and electrical properties. In order to avoid such a problem relating to moisture-absorbing solder resistance, for example, it is possible to take measures to preliminarily dry the FPC and remove moisture before the mounting process. However, since the number of processes increases, there is a problem in terms of productivity.

  In order to solve the above problems, the present inventors have found that the moisture absorption solder resistance can be improved by imparting crystallinity to the thermoplastic polyimide used in the adhesive layer. However, when a thermoplastic polyimide having crystallinity is used, a new problem occurs. As one method for producing an adhesive film for a two-layer FPC, there is a method in which a solution containing polyamic acid, which is a precursor of thermoplastic polyimide, is applied to a heat-resistant polyimide film and dried, and then the polyamic acid is imidized. However, when a thermoplastic polyimide having crystallinity is used, the adhesion between the heat-resistant polyimide film and the adhesive layer may not be sufficiently ensured.

The above-mentioned problems can be improved by performing plasma treatment or corona treatment for improving adhesion, but it is not sufficient to include variations in quality.
Japanese Patent Laid-Open No. 2-180682

  The present invention has been made in view of the above, and the purpose thereof is to ensure sufficient adhesion with a heat-resistant polyimide film as a base even when crystalline thermoplastic polyimide having crystallinity is used for an adhesive layer. Another object of the present invention is to provide an adhesive film excellent in moisture-absorbing solder resistance and a flexible metal-clad laminate obtained by using the adhesive film.

  As a result of intensive studies in view of the above problems, the present inventors control the drying temperature at the time of applying and drying a solution containing polyamic acid, which is a precursor of thermoplastic polyimide, to a heat-resistant polyimide film within an appropriate range. As a result, it was found that the adhesion between the adhesive layer and the base film layer of the obtained adhesive film can be improved, and the present invention has been completed.

  That is, in the present invention, an adhesive layer is provided by applying and drying a solution containing polyamic acid, which is a precursor of thermoplastic polyimide, on at least one surface of a heat-resistant polyimide film and then imidizing the polyamic acid. An adhesive film, wherein (i) the heat-resistant polyimide film has been subjected to corona treatment or plasma treatment; (ii) after being applied in the step of applying and drying a solution containing polyamic acid to the heat-resistant polyimide film; (Iii) The final drying temperature in the coating / drying step is “the boiling point of the solvent used in the solution containing the polyamic acid−30” ° C. or higher. iv) Adhesion characterized in that it is manufactured by satisfying that the thermoplastic polyimide having crystallinity is contained in the adhesive layer. On Irumu.

  A preferred embodiment relates to the above adhesive film, wherein the melting point of the thermoplastic polyimide is in the range of 350 to 450 ° C.

  A preferred embodiment relates to any one of the above adhesive films, wherein the thermoplastic polyimide having crystallinity is contained in a range of 85 to 100% by weight based on the thermoplastic polyimide contained in the adhesive layer. .

  In a preferred embodiment, the crystalline thermoplastic polyimide has 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 4,4′-bis ( 3-aminophenoxy) biphenyl, 4,4′-bis (4-aminophenoxy) biphenyl, units selected from 1,4-diaminobenzene, pyromellitic dianhydride as the acid dianhydride component, 3,3 ′, The present invention relates to any one of the above adhesive films, wherein the adhesive film is obtained by imidizing a polyamic acid composed of a combination of units selected from 4,4′-biphenyltetracarboxylic dianhydride.

  The present invention is obtained by laminating a metal foil to any one of the above adhesive films, and is 40 ° C., 90% R.D. H. The present invention relates to a flexible metal-clad laminate that does not cause appearance abnormalities such as blistering and whitening even if it is dipped in a 300 ° C. solder bath for 10 seconds after moisture absorption for 96 hours.

  In a preferred embodiment, when the melting point of the crystalline thermoplastic polyimide contained in the adhesive layer is T (° C.), the bonding of the adhesive film and the metal foil is any one in the range of (T-40) ° C. to T ° C. Even if it implements at temperature, it is related with the said flexible metal-clad laminated board characterized by the metal foil peeling strength being 10 N / cm or more by 90 degree | times direction peeling.

  The adhesive film obtained by the present invention and the flexible metal-clad laminate produced by bonding a metal foil thereto are excellent in adhesiveness and moisture absorption solder resistance.

  Embodiments of the present invention will be described below.

<Heat resistant polyimide film>
The “heat-resistant polyimide film” used in the adhesive film according to the present invention may be formed by containing 90% by weight or more of non-thermoplastic polyimide, and the molecular structure and thickness of non-thermoplastic polyimide are not particularly limited. . The non-thermoplastic polyimide used for forming the heat-resistant polyimide film is generally produced using polyamic acid as a precursor. However, the non-thermoplastic polyimide may be completely imidized or imide An unconverted precursor, that is, a polyamic acid, may be included in part. Here, the non-thermoplastic polyimide generally refers to a polyimide that does not soften or show adhesiveness even when heated. In the present invention, it refers to a polyimide that is heated in a film state at 450 ° C. for 2 minutes, does not wrinkle or stretch, and maintains its shape, or has substantially no glass transition temperature. The glass transition temperature can be obtained from the value of the inflection point of the storage elastic modulus measured by a dynamic viscoelasticity measuring device (DMA). Further, “substantially has no glass transition temperature” means that thermal decomposition starts before the glass transition state is reached.

  The thickness of the heat-resistant polyimide film can be appropriately selected depending on the application. In general, in a two-layer FPC, the insulating layer thickness (the thickness obtained by adding the heat-resistant polyimide film and the adhesive layer) is 1 mil (25 μm), half-mill ( Since the thickness of 12.5 μm is preferably used, the thickness of the heat-resistant polyimide film is preferably in the range of 7 to 18 μm.

  It does not specifically limit about the heat resistant polyimide film which can be used in the adhesive film which concerns on this invention, For example, it is possible to use the well-known polyimide film marketed. Examples of commercially available polyimide films include “Apical” (manufactured by Kaneka), “Kapton” (manufactured by DuPont, Toray DuPont), “Iupilex” (manufactured by Ube Industries), and the like. Of course, you may use the heat resistant polyimide film suitably produced using the conventionally well-known raw material or a manufacturing method. For example, the aromatic tetracarboxylic dianhydride and the aromatic diamine are usually dissolved in an organic solvent in a substantially equimolar amount, and the aromatic tetracarboxylic dianhydride is controlled under controlled temperature conditions. The polyamic acid varnish as a precursor is produced by stirring until the polymerization of the diamine with the aromatic diamine is completed, and a heat-resistant polyimide film can be obtained using the polyamic acid varnish.

  The heat-resistant polyimide film that can be used in the adhesive film according to the present invention is subjected to (i) corona treatment or plasma treatment from the viewpoint of improving adhesion. Corona treatment and plasma treatment are well-known techniques, and since there is a lot of knowledge about treatment on polyimide films, treatment conditions may be applied as appropriate.

<Adhesive layer of adhesive film>
The adhesive film according to the present invention is formed by providing an adhesive layer containing a thermoplastic polyimide on at least one surface of a heat-resistant polyimide film. (Iv) The thermoplastic polyimide contained in the adhesive layer It is characterized in that at least a part or all of it is a thermoplastic polyimide having crystallinity.

  In the present invention, “having crystallinity” means a clear endothermic peak (this peak temperature is defined as a melting point) due to a transition from a solid state to a molten state in differential scanning calorimetry (DSC) measurement. ). In contrast, amorphous thermoplastic polyimide is different in that it has no melting point and therefore does not show a clear endothermic peak, and only a slight endotherm is observed near the glass transition temperature.

  Amorphous thermoplastic polyimide generally exhibits a behavior in which the storage elastic modulus rapidly decreases and softens in the vicinity of the glass transition temperature. Therefore, when only amorphous thermoplastic polyimide is used as the thermoplastic polyimide contained in the adhesive layer of the adhesive film, this causes moisture in the adhesive film to suddenly pass through the adhesive layer. As a result, it may cause whitening or swelling of the adhesive film or the flexible metal-clad laminate. In order to prevent this, it is necessary to raise the glass transition temperature of the thermoplastic polyimide to near the temperature in the component mounting process on the FPC using, for example, solder. On the other hand, when manufacturing a flexible metal-clad laminate, At the temperature at which the adhesive film and the metal foil are bonded, the adhesive layer needs to be sufficiently softened in order to exhibit adhesiveness. In order to bond the adhesive film and the metal foil with high productivity, it is necessary to bond the adhesive film and the metal foil at a temperature about 80 to 150 ° C. higher than the glass transition temperature of the thermoplastic polyimide used for the adhesive layer of the adhesive film. In this way, improvement in moisture-absorbing solder resistance and workability in the production of metal-clad laminates using adhesive films are contradictory, so in order to achieve both, the glass transition temperature of thermoplastic polyimide is strictly controlled. However, in recent years, as the required temperature for moisture-absorbing solder resistance increases, it becomes increasingly difficult to obtain adhesive films and flexible metal-clad laminates that have both moisture-absorbing solder resistance and workability. there were.

  On the other hand, crystalline thermoplastic polyimide has a lower degree of storage modulus near the glass transition temperature than amorphous thermoplastic polyimide, and generally has a storage modulus suddenly near the melting point higher than the glass transition temperature. There is a tendency to decrease. For this reason, it is possible to make it easier to achieve both hygroscopic solder resistance and workability as compared with the case where amorphous thermoplastic polyimide is used for the adhesive layer. Conventionally, crystalline thermoplastic polyimide has been used for molded products such as melt extrusion molding and injection molding, but it is rarely used for electronic materials used in different technical fields as in the present invention, and is resistant to moisture absorption solder. Until now, there has been no known technique that focuses on the correlation between the crystallinity of thermoplastic polyimide.

  The adhesive film according to the present invention can exhibit excellent moisture-absorbing solder resistance when FPC is used. For this reason, the melting point of the crystalline thermoplastic polyimide contained in the adhesive layer is preferably at least a certain level. Specifically, the melting point is preferably in the range of 350 to 450 ° C, and more preferably in the range of 370 to 420 ° C. When the melting point is lower than the above range, the temperature at which the adhesive layer begins to soften also becomes low, and thus the moisture absorption solder resistance may not be improved sufficiently. Conversely, when the melting point is higher than the above range, the adhesive layer may not be sufficiently softened at the temperature at which the metal foil and the adhesive film are bonded together, and the adhesive strength of the metal foil to the adhesive film may be reduced.

  The crystalline thermoplastic polyimide contained in the adhesive layer in the adhesive film of the present invention can be obtained by imidizing the precursor polyamic acid. The method for producing the polyamic acid is not particularly limited, and a conventionally known method can be used. As a general example, there can be mentioned a method in which a diamine component and an acid dianhydride component are mixed in an organic solvent, and a polyamic acid organic solvent solution is obtained by a polymerization reaction. By appropriately selecting the structure of the diamine component and acid dianhydride component used here, it is possible to impart crystallinity to the thermoplastic polyimide obtained by imidizing the polyamic acid obtained by polymerizing them. It becomes. However, as described above, since polyimide is generally obtained by a polymerization reaction of a diamine component and an acid dianhydride component, if either one of the specific diamine component or acid dianhydride component is used, a crystalline polyimide is always produced. Although not obtained, the expression of crystallinity greatly depends on the combination of a specific diamine component and an acid dianhydride component.

  Taking into account that there is a viewpoint of the above combination, examples of the diamine component and the acid dianhydride component that can be used as a raw material for the crystalline thermoplastic polyimide contained in the adhesive layer in the present invention are as follows: As 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 4,4′-bis (3-aminophenoxy) biphenyl, 4,4′-bis ( Ether-based diamines such as 4-aminophenoxy) biphenyl and phenylene-based diamines such as 1,4-diaminobenzene are preferred because they tend to exhibit crystallinity. On the other hand, as the acid dianhydride component, pyromellitic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and the like are preferable because they tend to exhibit crystallinity. Of course, the diamine component and the acid dianhydride component used as raw materials for the thermoplastic polyimide of the present invention are not limited to these, and the heat obtained as a result of a specific combination of the diamine component and the acid dianhydride component. As long as the plastic polyimide exhibits crystallinity, a raw material having another structure may be used.

  In the present invention, a particularly preferred combination of a diamine component and an acid dianhydride component as raw materials for obtaining a crystalline thermoplastic polyimide is, for example, 1,4-bis (4-aminophenoxy) benzene, 1,3- A combination of bis (4-aminophenoxy) benzene and 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride can be exemplified.

  In the present invention, the conditions relating to the organic solvent used for the polymerization of the polyamic acid which is the precursor of the thermoplastic polyimide, the polymerization temperature, the polymerization concentration, etc. are not particularly limited, and can be produced under conventionally known conditions. is there.

  In the present invention, the thermoplastic polyimide contained in the adhesive layer is characterized in that at least a part or all of it is a crystalline thermoplastic polyimide. Especially, it is preferable that crystalline thermoplastic polyimide is contained in 85 weight%-100 weight% from a viewpoint of moisture absorption solder resistance and workability on the basis of the amount of the thermoplastic polyimide, and also 90 weight%-100. More preferably, it is contained in the range of% by weight.

  The adhesive layer of the adhesive film according to the present invention may contain organic / inorganic particles such as a filler, for example, for the purpose of controlling the linear expansion coefficient and slipperiness, in addition to the thermoplastic polyimide, if necessary. In this case, for example, the amount of filler added is preferably in the range of 0.001 to 10% by weight with respect to the adhesive layer.

<Manufacture of adhesive film>
The adhesive film according to the present invention is obtained by applying a solution containing polyamic acid, which is a precursor of thermoplastic polyimide, to at least one surface of a heat-resistant polyimide film, and then imidizing the polyamic acid after drying. is there. Here, the drying temperature in the drying step after the solution containing the polyamic acid is applied to the heat-resistant polyimide film is set to (ii) the initial drying temperature is set to 100 ° C. or higher, (iii) the final drying temperature is set to “polyamide” Necessary for improving the adhesion between the heat-resistant polyimide film (also referred to as a base film) and the adhesive layer in the resulting adhesive film, that is, the boiling point of the solvent used in the acid solution is −30 ”° C. or higher. .

  For example, when non-crystalline thermoplastic polyimide is used for the adhesive layer, the adhesiveness between the base film and the adhesive layer in the obtained adhesive film does not change even if the above drying conditions are not adopted. . However, the present inventors have found that when crystalline thermoplastic polyimide is used for the adhesive layer as described above, the drying conditions of the polyamic acid greatly affect the adhesion between the base film and the adhesive layer. A manufacturing method is known in which a polyamic acid solution of a thermoplastic polyimide precursor is applied to a heat-resistant polyimide film, dried, and then heated to imidize. However, the conventional technology uses non-crystalline thermoplastic polyimide for the adhesive layer. As described above, the polyamic acid solution is applied to the heat-resistant polyimide film and dried for the adhesion between the base film and the adhesive layer. It does not affect the drying conditions in the process. When crystalline thermoplastic polyimide is used as the adhesive layer in the adhesive film, the drying conditions of the solution containing the polyamic acid that is the precursor greatly affects the adhesion of the resulting adhesive film. It was discovered for the first time.

  Note that it is not clear why the drying temperature of the solution containing the polyamic acid as a precursor greatly affects the adhesion only when a crystalline thermoplastic polyimide is used. However, the behavior of the molecular chain of the polyamic acid precursor is different between crystalline and amorphous thermoplastic polyimides, which affects the adhesion and further affects the adhesion of the resulting adhesive film. It is thought that it is.

  The initial drying temperature in the step (ii) of applying and drying a solution containing polyamic acid on the heat-resistant polyimide film is preferably 105 ° C. or higher, more preferably 110 ° C. or higher. The upper limit of the initial drying temperature is preferably “boiling point of solvent used in polyamic acid solution−30” ° C. When the initial drying temperature is lower than the above range, the effect of improving the adhesion may not be sufficiently exhibited. On the other hand, when the initial drying temperature exceeds the above upper limit value, the solvent rapidly evaporates at the initial stage of the drying process, foaming may occur, and the appearance of the resulting adhesive film may deteriorate.

  On the other hand, the final drying temperature in the coating and drying step (iii) is preferably “boiling point of solvent used in polyamic acid solution −20” ° C. or higher, and further “used in polyamic acid solution”. More preferably, the boiling point of the solvent is −10 ”° C. or higher. The upper limit of the final drying temperature is preferably not higher than the boiling point of the solvent used in the polyamic acid solution + 20 ”° C. or lower. When the final drying temperature is lower than the above range, the effect of improving the adhesion may not be sufficiently exhibited. On the other hand, when the final drying temperature exceeds the above upper limit value, a portion where the imidization of the adhesive layer partially proceeds starts to occur, and thus the adhesive film finally obtained through the subsequent heating imidization step The characteristics may be non-uniform. In addition, when there are a plurality of solvents used in the polyamic acid solution, the drying temperature is adjusted according to the solvent having the higher boiling point.

  For the step of applying and drying the solution containing the polyamic acid to the heat-resistant polyimide film and the step of imidization by heating, it is not necessary to use a special apparatus, and conventionally known ones can be used.

  Further, the thickness of the adhesive layer in the adhesive film according to the present invention is not limited. The thickness may be appropriately selected in consideration of the thickness of the entire adhesive film, the surface roughness of the metal foil to be bonded, etc., but the range of 1 to 10 μm is preferable, and the range of 1.5 to 6 μm is more preferable. Even if the adhesive layer is made thicker than the above range, the adhesive strength is not proportionally improved, and conversely, it may be difficult to control the linear expansion coefficient of the entire adhesive film. If the adhesive layer is thinner than the above range, the adhesive layer may not sufficiently bite into the irregularities on the surface of the metal foil, resulting in poor adhesion.

<Flexible metal-clad laminate>
The flexible metal-clad laminate according to the present invention can be obtained, for example, by attaching a metal foil to the adhesive film. The metal foil to be used is not particularly limited, but when the flexible metal-clad laminate of the present invention is used for electronic equipment / electric equipment, for example, copper or copper alloy, stainless steel or its alloy, nickel Alternatively, a metal foil made of nickel alloy (including 42 alloy), aluminum, or aluminum alloy can be used. In general flexible metal-clad laminates, copper foil such as rolled copper foil and electrolytic copper foil is frequently used, but it can also be preferably used in the present invention. In addition, the antirust layer, the heat-resistant layer, or the contact bonding layer may be apply | coated to the surface of these metal foil.

  In the present invention, the thickness of the metal foil is not particularly limited, and may be any thickness as long as a sufficient function can be exhibited depending on the application.

  The method for bonding the adhesive film and the metal foil is not particularly limited, and for example, a continuous process using a hot roll laminating apparatus having a pair of metal rolls or a double belt press (DBP) can be used. Among these, it is preferable to use a hot roll laminating apparatus having a pair of metal rolls because the apparatus configuration is simple and advantageous in terms of maintenance cost. The “heat roll laminating apparatus having a pair of metal rolls” herein may be an apparatus having a metal roll for heating and pressurizing a material, and the specific apparatus configuration is particularly limited. It is not a thing.

  The flexible metal-clad laminate according to the present invention is, for example, 40 ° C., 90% R.D. H. After absorbing moisture for 96 hours under the above humidifying conditions, even if immersed in a solder bath at 300 ° C. for 10 seconds, performance that does not cause abnormal appearance such as swelling and whitening can be exhibited.

  Furthermore, when the melting point of the crystalline thermoplastic polyimide contained in the adhesive layer is T (° C.), the bonding between the adhesive film and the metal foil is any temperature within the range of (T-40) ° C. to T ° C. Even if it implements in, it is preferable that metal foil peeling strength is 10 N / cm or more by 90 degree | times direction peeling. When crystalline thermoplastic polyimide is used for the adhesive layer, the temperature required for metal foil bonding tends to be higher than when amorphous thermoplastic polyimide is used. However, if the drying temperature at the time of adhesive film production is properly controlled, not only the adhesion between the base film and the adhesive layer is ensured, but the temperature required for bonding can also be lowered somewhat. It becomes.

  The flexible metal-clad laminate according to the present invention is compatible with both physical properties of adhesiveness and moisture absorption solder resistance, and can be used for FPC compatible with lead-free solder or multilayer FPC. Of course, the application of the present invention is not limited to this, and it goes without saying that it can be used for various applications as long as it is a laminate including a metal foil.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to these. The melting point (Tm), glass transition temperature (Tg) of the thermoplastic polyimide used in the adhesive layers in the examples and comparative examples, the hygroscopic solder resistance of the flexible metal-clad laminate, and the peel strength of the metal foil are as follows: Measured or evaluated as follows.

[Melting point of thermoplastic polyimide]
The thermoplastic polyimide precursor solution obtained in the synthesis example was cast on a shine surface of 18 μm rolled copper foil (BHY-22B-T, manufactured by Nikko Metal Co., Ltd.) so that the final thickness was 20 μm. Drying was performed at 200 ° C for 2 minutes, 250 ° C for 2 minutes, 300 ° C for 2 minutes, and 350 ° C for 1 minute. After drying, the copper foil was removed by etching and dried at 50 ° C. for 30 minutes to obtain a single layer sheet of thermoplastic polyimide.

  Using the obtained thermoplastic polyimide single layer sheet, DSC220 manufactured by Seiko Instruments Inc. was used as a reference, and the temperature was increased from 0 ° C. to 450 ° C. at a temperature increase rate of 10 ° C./min and a temperature decrease rate of 40 ° C./min. The peak of the endothermic chart in the temperature raising step was taken as the melting point.

[Glass transition temperature of thermoplastic polyimide]
The measurement was performed in the same manner as the melting point measurement, and the inflection point of the endothermic chart in the temperature raising step was defined as the glass transition temperature.

[Hygroscopic solder resistance of flexible metal-clad laminate]
For the double-sided flexible metal-clad laminates obtained in the examples and comparative examples, the excess copper foil layer was removed by etching treatment so that the upper and lower copper foil layers overlap each other with a size of 1 cm × 1.5 cm. Two were produced. The obtained sample was 40 ° C., 90% R.D. H. The sample was left for 96 hours under the humidification conditions, to perform a moisture absorption treatment. After the moisture absorption treatment, the sample was immersed in a solder bath at 250 ° C., 270 ° C., and 300 ° C. for 10 seconds. For each sample after solder immersion, the copper foil layer on one side is removed by etching, and the appearance of the part where the copper foil overlaps is unchanged (good), whitening of the adhesive film layer, swelling, copper foil layer When any of the above peelings was confirmed, it was set as x (bad).

[Metal foil peel strength of flexible metal-clad laminate]
A sample was prepared according to “6.5 Peel Strength” of JIS C6471, and a 5 mm wide metal foil part was peeled off at a peeling angle of 90 degrees and 50 mm / min, and the load was measured. After the measurement, the peeling interface of the sample was confirmed, and the case of peeling at the interface between the adhesive layer and the base film was designated as A / PI, and the case of peeling at the interface between the adhesive layer and the copper foil was designated as C / A.

(Synthesis Example 1; Synthesis of thermoplastic polyimide precursor)
637.0 g of N, N-dimethylformamide (hereinafter also referred to as DMF, boiling point 153 ° C.), 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (hereinafter referred to as BPDA) in a glass flask having a capacity of 2000 ml. 28.2 g of 1,4-bis (4-aminophenoxy) benzene (hereinafter, also referred to as TPE-Q) and 1,3-bis ( 45.4 g of 4-aminophenoxy) benzene (hereinafter also referred to as TPE-R) was added and stirred at 25 ° C. for 1 hour. A solution in which 2.0 g of TPE-R was dissolved in 27.0 g of DMF was separately prepared, and this was gradually added to the above reaction solution while paying attention to the viscosity and stirred. When the viscosity reached 1200 poise, the addition and stirring were stopped to obtain a polyamic acid solution. Using the obtained polyamic acid solution, a glass transition temperature and a melting point measurement sample of thermoplastic polyimide were prepared and measured. As a result, it was confirmed that the glass transition point was 230 ° C. and the melting point was 400 ° C. It turns out to have.

(Synthesis Example 2: Synthesis of thermoplastic polyimide precursor)
While adding 632.4 g of DMF and 56.8 g of BPDA to a glass flask having a capacity of 2000 ml, stirring under a nitrogen atmosphere, 2,2-bis [4- (4-aminophenoxy) phenyl] propane (hereinafter also referred to as BAPP). 76.8 g) was added and stirred at 25 ° C. for 1 hour. A solution prepared by dissolving 2.4 g of BAPP in 31.6 g of DMF was separately prepared, and this was gradually added to the above reaction solution while paying attention to the viscosity and stirred. When the viscosity reached 1200 poise, the addition and stirring were stopped to obtain a polyamic acid solution. Using the obtained polyamic acid solution, a glass transition temperature and a melting point measurement sample of a thermoplastic polyimide were prepared and measured. As a result, a glass transition point was shown at 240 ° C., but a melting point endothermic peak was not confirmed. I found that I do not have it.

Example 1
The polyamic acid solution obtained in Synthesis Example 1 was diluted with N, N-dimethylacetamide (hereinafter also referred to as DMAc, boiling point 165 ° C.) until the solid content concentration became 8.0 wt%. The polyamic acid solution is continuously applied with a die coater so that the final single-side thickness is 4 μm while the film is fed out from a roll of a 17 μm-thick heat-resistant polyimide film (Apical 17FPP, manufactured by Kaneka). It was. The coated film was passed through a drying furnace installed with the die coater, and dried at an initial drying temperature: 110 ° C. for 20 seconds, 145 ° C. for 20 seconds, and a final drying temperature: 150 ° C. for 40 seconds. . The dried film was again wound into a roll, and the polyamic acid solution was similarly applied to the opposite surface and dried. The film was drawn out from a film roll that had been coated and dried with a polyimide acid solution on both sides, and imidized by continuously passing through a heating furnace set at a furnace temperature of 420 ° C. to obtain an adhesive film.

  12 μm electrolytic copper foil (F2-WS; manufactured by Furukawa Circuit Foil) is disposed on both sides of the obtained adhesive film, and protective materials (Apical 125 NPI; manufactured by Kaneka) are further disposed on both sides thereof. Lamination temperatures were 340 ° C. and 380 ° C., a lamination pressure of 196 N / cm (20 kgf / cm), and a lamination rate of 1.5 m / min were continuously heat laminated to produce a flexible metal-clad laminate according to the present invention.

(Example 2)
The polyamic acid solution obtained in Synthesis Example 1 was diluted with a 1: 1 mixed solvent of 1,3-dioxolane (boiling point 74 ° C.) and DMF until the solid content concentration was 6.0% by weight. While feeding the film from a roll of a 17 μm-thick heat-resistant polyimide film (Apical 17FPP, Kaneka) that has been plasma-treated, the polyamic acid solution is continuously applied with a gravure coater so that the final single-sided thickness is 4 μm. It was. The coated film was passed through a drying furnace installed with the coater, and dried at an initial drying temperature: 110 ° C. for 20 seconds, 130 ° C. for 20 seconds, and a final drying temperature: 150 ° C. for 20 seconds. The dried film was again wound into a roll, and the polyamic acid solution was similarly applied to the opposite surface and dried. The film was drawn out from a film roll that had been coated and dried with a polyimide acid solution on both sides, and imidized by continuously passing through a heating furnace set at a furnace temperature of 420 ° C. to obtain an adhesive film. Using the resulting adhesive film, the same operation as in Example 1 was performed to obtain an adhesive film and a flexible metal-clad laminate.

(Example 3)
The polyamic acid solution obtained in Synthesis Example 1 was diluted with a 1: 1 mixed solvent of 1,3-dioxolane and DMF until the solid content concentration became 8.5% by weight. A plasma-treated 17 μm-thick heat-resistant polyimide film (Apical 17FPP, manufactured by Kaneka Co., Ltd.) was cut into a size of 30 cm × 40 cm, and continuously coated using a comma coater so that the final single-sided thickness was 4 μm. The coated film was dried for 60 seconds in an oven at an initial and final drying temperature of 130 ° C. In the same manner, the polyamic acid solution was applied to the opposite surface and dried. The polyimide acid solution applied on both sides and dried were heated in an oven at 420 ° C. for 20 seconds for imidization treatment to obtain an adhesive film. Using the resulting adhesive film, the same operation as in Example 1 was performed to obtain an adhesive film and a flexible metal-clad laminate.

(Comparative Example 1)
A polyimide film not subjected to corona treatment or plasma treatment (Apical 17FP, manufactured by Kaneka) is used as a heat-resistant polyimide film, and drying after coating with a die coater is performed at an initial drying temperature of 80 ° C. for 40 seconds and 120 ° C. for 20 seconds. Second, final drying temperature: The same operation as in Example 1 was carried out except that it was carried out at 150 ° C. for 40 seconds to obtain an adhesive film and a flexible metal-clad laminate.

(Comparative Example 2)
The adhesive film was subjected to the same operation as in Example 1 except that drying after coating with a die coater was performed at initial drying temperature: 80 ° C. for 40 seconds, 120 ° C. for 20 seconds, and final drying temperature: 150 ° C. for 40 seconds. In addition, a flexible metal-clad laminate was obtained.

(Comparative Example 3)
Adhesion after coating with a gravure coater was carried out in the same manner as in Example 2 except that the initial drying temperature was 80 ° C. for 20 seconds, 100 ° C. for 20 seconds, and the final drying temperature was 130 ° C. for 20 seconds. Films and flexible metal-clad laminates were obtained.

(Comparative Example 4)
The adhesive film and the flexible metal-clad laminate were the same as in Example 3 except that drying after coating with a comma coater was performed at an initial drying temperature: 80 ° C. for 30 seconds and a final drying temperature: 130 ° C. for 30 seconds. Got.

(Comparative Example 5)
Instead of the polyamic acid solution obtained in Synthesis Example 1, the polyamic acid solution obtained in Synthesis Example 2 was used, and a polyimide film not subjected to corona treatment or plasma treatment as a heat-resistant polyimide film (Apical 17FP, manufactured by Kaneka Corporation) ) Was used in the same manner as in Example 1 to obtain an adhesive film and a flexible metal-clad laminate.

(Comparative Example 6)
An adhesive film and a flexible metal-clad laminate were obtained in the same manner as in Example 1 except that the polyamic acid solution obtained in Synthesis Example 2 was used instead of the polyamic acid solution obtained in Synthesis Example 1. It was.

  Table 1 shows the results of evaluating the melting point (Tm) and glass transition temperature (Tg) of the thermoplastic polyimide used for the adhesive layer of the adhesive film, and the characteristics of the flexible metal-clad laminates obtained in each example and comparative example. .

  As shown in Comparative Examples 1 to 4, when the initial drying temperature after application of the polyamic acid solution is lower than a specific value, the metal foil peel strength (adhesiveness between the adhesive layer and the base film) is good although the moisture absorption solder resistance is not a problem. It can be seen that it is low, particularly when the bonding temperature between the adhesive film and the metal foil is low. On the other hand, in the Example which made the initial drying temperature after polyamic acid solution application | coating 100 degreeC or more, even if the bonding temperature of an adhesive film and metal foil was low, sufficient metal foil peeling strength was shown. Note that the peeling interface is A / PI with no change between the examples and the comparative examples, and it can be understood that the adhesion between the base film and the adhesive layer is improved by optimizing the drying conditions.

  On the other hand, Comparative Examples 5 to 6 using an amorphous thermoplastic polyimide are not affected by the drying conditions and have the same adhesiveness, and the drying conditions are affected only when the crystalline thermoplastic polyimide is used. Is shown.

Claims (6)

An adhesive film provided with an adhesive layer on at least one surface of a heat-resistant polyimide film by applying and drying a solution containing polyamic acid which is a precursor of thermoplastic polyimide, and then imidizing the polyamic acid, The solvent used in the solution containing the polyamic acid includes at least one selected from the group consisting of N, N-dimethylformamide and N, N-dimethylacetamide, and includes all of the following (i) to (iv): An adhesive film characterized by being manufactured by being filled.
(I) The heat resistant polyimide film is subjected to corona treatment or plasma treatment.
(Ii) In the step of applying and drying the solution containing polyamic acid to the heat-resistant polyimide film, the initial drying temperature after application is set to 100 ° C. or higher and 130 ° C. or lower.
(Iii) The final drying temperature in the coating / drying step is “the boiling point of the solvent used in the polyamic acid-containing solution −30” ° C. or higher.
(Iv) Crystalline thermoplastic polyimide is contained in the adhesive layer.   The adhesive film according to claim 1, wherein the melting point of the thermoplastic polyimide is in the range of 350 to 450 ° C.   The adhesive film according to claim 1 or 2, wherein the thermoplastic polyimide having crystallinity is contained in a range of 85 to 100% by weight based on the thermoplastic polyimide contained in the adhesive layer.   Crystalline thermoplastic polyimide has 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 4,4′-bis (3-aminophenoxy) as the diamine component. Units selected from biphenyl, 4,4′-bis (4-aminophenoxy) biphenyl, and 1,4-diaminobenzene, pyromellitic dianhydride as the acid dianhydride component, and 3,3 ′, 4,4 The adhesive film according to any one of claims 1 to 3, wherein the adhesive film is obtained by imidizing a polyamic acid composed of a combination of units selected from '-biphenyltetracarboxylic dianhydride.   It is obtained by bonding a metal foil to the adhesive film according to any one of claims 1 to 4, and is 40 ° C and 90% R.D. H. A flexible metal-clad laminate that does not cause abnormal appearance such as blistering or whitening even if it is dipped in a solder bath at 300 ° C. for 10 seconds after moisture absorption for 96 hours under the above humidifying conditions.   When the melting point of the crystalline thermoplastic polyimide contained in the adhesive layer is T (° C.), the adhesive film and the metal foil are bonded at any temperature in the range of (T-40) ° C. to T ° C. The flexible metal-clad laminate according to claim 5, wherein the metal foil peeling strength is 10 N / cm or more when peeled in the 90 ° direction.