JP4731107B2 - Flexible metal foil laminate - Google Patents

Description

  The present invention relates to a flexible metal foil laminate. More specifically, the present invention relates to a flexible metal foil laminate that has a small dimensional change rate due to thermal shrinkage and its variation and is suitably used as a substrate material for forming a fine pitch circuit.

  2. Description of the Related Art In recent years, electronic devices with high performance, high functionality, and miniaturization are rapidly progressing, and there is an increasing demand for miniaturization and weight reduction of electronic components used in electronic devices. Along with this, improvements in various physical properties such as heat resistance, mechanical strength, and electrical characteristics are also required for the materials of electronic components, and the semiconductor element packaging method and the wiring board on which they are mounted also have higher density and higher performance. There is a growing demand for functional and high performance.

  In particular, liquid crystal displays mounted on small electronic devices such as mobile phones and digital cameras are becoming more high-definition and high-speed driving, so the driving IC has a very fine bump pitch and is mounted on it. A fine pitch is also required for flexible printed circuit boards. In order to ensure the reliability of the connection portion between the fine pitch driving IC and the flexible printed board, the flexible printed board is required to have high dimensional stability.

  Generally, a flexible printed circuit board is formed by forming a wiring by photoetching a flexible metal foil laminate consisting of a laminate of a metal foil and a resin layer, and covering and protecting the wiring with a film or liquid coverlay. Accordingly, the terminal portion is formed by plating with gold, tin, solder or the like. It is known that the dimensional stability of the flexible printed circuit board is mainly caused by the shrinkage rate of the resin layer that becomes the insulating base of the flexible metal foil laminate.

  The resin layer to be laminated on the flexible metal foil laminate is mainly made of polyimide resin, polyester resin, glass epoxy resin, polyphenylene sulfide resin, liquid crystal polymer, etc., and industrially inexpensive polyester for applications that do not require heat resistance. Polyimide resins are most often used in applications where resins are required and heat resistance is required.

  A polyimide resin obtained by polycondensation of an aromatic tetracarboxylic dianhydride and an aromatic diamine is known as a polymer having excellent heat resistance. In the process of producing a metal foil resin laminate represented by a copper-clad plate, an organic solvent solution of polyamic acid obtained by reacting these raw materials is applied to the metal foil, and then heated to evaporate the solvent. At the same time, a method for completing the polyimidation reaction or a method for evaporating the solvent after applying the polyimide resin organic solvent solution to the metal foil when the polyimide resin is soluble in the organic solvent are used. Alternatively, a method in which a thermoplastic polyimide resin film is brought into contact with a metal foil and a double-sided metal foil polyimide resin laminate is formed by heat fusion has been industrialized.

  However, in all of these methods, the resin part is always exposed to a temperature not lower than the glass transition point Tg and cooled. At this time, an unrelaxed volume due to rapid cooling inevitably remains, and shrinkage cannot be avoided due to a thermal history in the heating process in the mounting process. In particular, recently, a metal foil resin laminate having a small shrinkage due to heat is desired due to the fine patterning of a flexible printed circuit board, and at the same time, a small dimensional change due to a temperature change is also desired.

As a typical method for reducing shrinkage due to heat, many methods of performing thermal annealing as described in Patent Documents 1 to 7 are employed. What can be said in common with these methods is that the heat treatment conditions consisting of the heat treatment temperature and the heat treatment time are wide, and naturally the optimum heat treatment conditions differ for different types of resin layers. Will be. Furthermore, it is considered that the heat treatment condition is a method of tuning by trial and error depending on the molecular structure of the resin, and it cannot be said that a clear heat treatment condition that theoretically reduces the amount of heat shrinkage is specified.
JP-A-54-108272 Japanese Patent Publication No. 07-040636 Japanese Patent Application Laid-Open No. 09-055567 JP 2000-072893 A JP 2000-202966 A JP 2001-177200 A JP 2001-270035 A

  The common point of these prior arts is to reduce the dimensional change due to heat of the resin part, but in addition to the amount of heat shrinkage, as an important characteristic value in design, there is variation in the amount of shrinkage due to heat. Is mentioned. As for thermal shrinkage, if the average value of the shrinkage is constant, the dimensions as designed can be obtained by correcting the design value, but naturally if the variation in shrinkage exceeds the allowable tolerance, Since the required dimensional accuracy cannot be obtained, the variation in the thermal shrinkage rate is an important evaluation item in securing the connection reliability between the IC and the flexible printed board. However, the fact is that conventionally, attention has not been paid to variations in the heat shrinkage rate.

  An object of the present invention is to provide a flexible metal foil laminate capable of forming a flexible printed circuit board having a fine pitch circuit suitable for mounting an IC having a high density pitch with little variation in dimensional change due to heat shrinkage. It is in.

An object of the present invention is a laminate of a metal foil and a resin layer made of a polyimide resin having a glass transition point Tg of 290 to 350 ° C. , which has a differential heat in an inert gas at a temperature rising rate of 10 ° C./min. When analysis (DSC) is performed, it is achieved by a flexible metal foil laminate in which the heat value of the endothermic peak observed in the glass transition region shows a value of 0.5 J / g or more per unit weight of the resin. Such a flexible metal foil laminate can be obtained by heat treatment for 8 hours or more at a temperature 5 to 50 ° C. lower than the glass transition point Tg of the resin.

  In order to obtain the dimensional stability required in the manufacturing process and mounting process of flexible printed circuit boards, a resin in a metastable state in a glass state is heat-treated at a temperature lower than the glass transition point Tg, and volume saturation, in other words, physical aging is performed. The present invention has found that the most effective effect can be obtained.

  The heat treatment conditions for ensuring dimensional stability depend on the glass transition point Tg depending on the skeleton structure of the polyimide resin. The effect of heat treatment at a temperature lower than the glass transition point Tg is the effect of the glass during DSC measurement. The present invention has found that the size of the endothermic peak observed in the temperature range of the transition point Tg is an index of dimensional stability (variation in dimensional change rate).

  Moreover, in order to make such an endothermic peak appear, it is achieved by performing heat treatment at a temperature 5 to 50 ° C. lower than the glass transition point Tg for at least 8 hours. Depending on the type of polyimide resin, a heat treatment of about 100 hours or more may be required to obtain a sufficient effect. The longer the processing time, the greater the peak intensity in the vicinity of the DSC Tg, but the peak intensity saturates with respect to the processing time when relaxation is sufficiently advanced.

  In general, the longer the processing time, the better the dimensional stability.However, when the physical aging is performed extremely, the thermal shrinkage of the volume decreases, but the fracture energy (integrated value of the ss curve) is slightly lower. To drop. Depending on the application, it may be necessary to consider the balance with mechanical properties, but within the scope of this technology for flexible printed circuit boards, a slight decrease in mechanical properties due to physical aging will not be a problem. is there.

Although structural stabilization by physical aging of engineering plastics is generally known, in the present invention, by the heat treatment for a long time below the glass transition point Tg, the absolute value of the heat shrinkage rate. It has been found that not only becomes smaller, but also the variation in heat shrinkage rate, that is, 3σ (σ: standard deviation) also becomes smaller. In the circuit design stage of a flexible printed circuit board that requires a fine pattern, the variation is more important than the thermal shrinkage rate itself, but the present invention clears this point.
Physics and Mechanics of Amorphous Polymers p. 206 and later (1998)

  The degree of structural stabilization by physical aging can be quantified by the amount of endothermic peak that appears in the vicinity of the glass transition point Tg when DSC measurement is performed at elevated temperature. And the larger this peak, the smaller the heat shrinkage rate and the smaller the variation. The relationship between the DSC peak near the glass transition point Tg by physical aging, the dimensional stability, and the effect of reducing the variation appears regardless of the structure of the polyimide resin. Even when two or more kinds of resins having different glass transition points Tg are used, dimensional stabilization can be achieved by long-term heat treatment at a temperature about 5 to 30 ° C. lower than the glass transition point Tg. The degree of the effect depends on the processing time and the processing temperature.

  By such heat treatment, the larger the amount of heat of the peak appearing near the glass transition point Tg, the larger the dimensional stabilization effect. Conversely, even if the treatment is performed for a long time at a temperature lower than the glass transition point Tg, It may not be observed. With such a resin, a dimensional stabilization effect by heat treatment cannot be expected.

As a result of heat treatment, if the heat quantity ΔH of the endothermic peak that appears near the glass transition point Tg shows a value of 0.5 J / g or more per unit weight of the resin, preferably 2.0 J / g or more, dimensional stability and its variation are reduced. The effect is fully confirmed. It should be noted that a resin material with a small amount of heat shrinkage should be treated in such a way that a peak of the 0.5 J / g level is observed, even if it slightly deviates from the design target value before the heat treatment. It is a fact that it becomes possible to put it into the specification by performing a heat treatment. That is, it can be said that it can be adopted in parallel with other dimensional stabilization methods.

As a dimensional stabilization method other than the heat treatment method, a method of coating a polyimide resin insulating layer in multiple layers has been industrialized, and even for such a multilayer resin, the resin component having the largest shrinkage is defined in the present invention. When the heat treatment is performed under such conditions, the heat shrinkability can be reduced.
Japanese Patent Laid-Open No. 08-250860 Japanese Patent Application Laid-Open No. 09-055567

  When a fine wiring pitch is required for the flexible printed circuit board, the reliability of the connection portion can be ensured by using the dimensionally stable polyimide resin film according to the present invention. In particular, since a heating step is included in the bonding step of the anisotropic conductive resin (ACF or the like), if a polyimide resin that causes thermal shrinkage is used, the connecting portion is displaced at the end portion. The present invention can be used for a fine pitch flexible printed circuit board without such fear.

  The effect of the present invention is a basic technique that enables the thermal shrinkage of amorphous resin products to be reduced, and is not only widely applicable, but also shows the heat shrinkage characteristics of heat treatment by the peak of the glass transition point Tg portion by thermal analysis. It can be said that it is groundbreaking in that the strength can be indicated. That is, the heat treatment conditions that had to be determined by trial and error for each resin material can be set in a unified way for any material. In addition, it can be said that it is significant to reduce the critical dimensional stability variation among the product design parameters.

  Further, the conditions under which the endothermic peak near the glass transition point Tg is observed are relatively narrow, and at temperatures lower by 50 ° C. from the glass transition point Tg, the endothermic peak is often not observed after about 10 hours of processing time. From this point of view, it can be said that the present invention has found a singular point of the condition when dimensional stabilization is achieved by heat treatment.

  Thus, in the present invention, the relaxation phenomenon of the unrelaxed volume due to the heat treatment just below the glass transition point Tg of the resin material is used, and the reason why the dimensional stability is expressed here is the heat generated by heat. The shrinkage is attributed to the shrinkage of the unrelaxed volume of the amorphous phase of the resin, and it is considered that the portion that tends to shrink is eliminated by removing this by local molecular relaxation in the glass state.

  Examples of the metal foil include electrolytic copper foil, rolled copper foil, aluminum foil, stainless steel foil, and the like. Generally, electrolytic copper foil or rolled copper foil is used. As the high-density flexible printed circuit board, it is preferable to use an electrolytic copper foil because it is excellent in fine pattern formation by copper etching. Since these metal foils are for flexible printed circuit boards, those having a thickness of about 3 to 35 μm are generally used, but those having a thickness of up to about 18 μm are preferably used for forming fine pitch wiring.

  The resin layer for laminating these metal foils on one or both sides is mainly formed from a polyimide resin, a polyester resin or the like, and preferably a polyimide resin is used. These resin layers are formed with a thickness of about 5 to 50 μm, preferably about 7 to 25 μm. If the thickness of the resin layer is less than this, the reliability of circuit insulation is poor, and mechanical properties such as bending are lowered. On the other hand, if a resin layer having a thickness greater than this is formed, foaming is likely to occur during heating, and flexibility is impaired.

  Regarding polyimide resin, the effect is not particularly limited by the structure of the polyimide resin, but the lead-free solder heat resistance temperature required for flexible printed circuit boards is 270 ° C and the use of anisotropic conductive adhesive (ACF) As a premise, the glass transition point Tg of the polyimide resin is preferably 290 ° C. or higher. When solder heat resistance is not required, the glass transition point Tg may be 240 ° C. or higher. On the other hand, the glass transition point Tg is desirably 350 ° C. or lower in consideration of heat fusion, solvent drying process, thermal decomposition of resin, and the like. In the heat treatment for a long time in this temperature region, the presence of oxygen becomes a problem, and thus heat treatment in an oxygen-free state such as in an inert gas is fundamental.

  In order to set the glass transition point Tg within the range of 290 to 350 ° C., the copolymer composition of the monomers constituting the polyimide resin is a problem, and considering heat resistance, the acid anhydride may be an aromatic tetracarboxylic dianhydride. Things are used. Examples of the aromatic tetracarboxylic dianhydride include pyromellitic dianhydride, 2,3,6,7-naphthalene tetracarboxylic dianhydride, and 3,3 ′, 4,4′-diphenyltetracarboxylic acid. Dianhydride, isopropylidenebis (4-phenyleneoxy-4-phthalic acid) dianhydride, 2,2'-bis (3,4-dicarboxyphenyl) propane dianhydride, bis (3,4-dicarboxy) Phenyl) sulfone dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, bis (3,4-carboxyphenyl) ether dianhydride, naphthalene-1,2,4,5-tetracarboxylic acid Dianhydride, naphthalene-1,4,5,8-tetracarboxylic dianhydride, decahydronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 4,8-dimethyl-1,2, 3,5,6,7-hexahydronaphthalene-1,2,5,6-tetracarboxylic dianhydride, 2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2 , 7- Dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, phenanthrene-1,8 , 9,10-tetracarboxylic dianhydride, 2,2-bis (2,3-dicarboxyphenyl) ethane dianhydride, 1,1-bis (3,4-dicarboxyphenyl) ethane dianhydride, Bis (2,3-dicarboxyphenyl) methane dianhydride, bis (3,4-dicarboxyphenyl) methane dianhydride, bis (3,4-dicarboxyphenyl) sulfone dianhydride, benzene-1,2 1,3,4-tetracarboxylic dianhydride, 3,4,3 ', 4'-benzophenone tetracarboxylic dianhydride, etc. are used alone or as a mixture of two or more.

  Examples of the aromatic diamine that reacts with these aromatic tetracarboxylic dianhydrides include 4,4′-diaminodiphenyl ether, m-phenylenediamine, p-phenylenediamine, 4,4′-diaminodiphenylpropane, 4 , 4'-diaminodiphenylmethane, benzidine, 4,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, 2,6-diaminopyridine, bis (4-aminophenyl) Diethylsilane, bis (4-aminophenyl) diphenylsilane, 3,3'-dichlorobenzidine, bis (4-aminophenyl) ethylphosphine oxide, bis (4-aminophenyl) phenylphosphine oxide, bis (4-aminophenyl) ) -N-phenylamine, bis (4-aminophenyl) -N-methylamine, 1,5-diaminonaphthalene, 3,3'-dimethyl -4,4'-diaminobiphenyl, 3,4'-dimethyl-3 ', 4-diaminobiphenyl, 3,3'-dimethoxybenzidine, 2,4-bis (β-amino-tert-butyl) toluene, bis (p-β-amino-tert-butylphenyl) ether, p-bis (2-methyl-4-aminobenzyl) benzene, p-bis (1,1-dimethyl-5-aminobenzyl) benzene, m-xylylene diene Amine, p-xylylenediamine, 1,3-diaminoadamantane, 3,3'-diamino-1,1'-diadamantane, 3,3'-diamino-1,1'-diadamantane, bis (p-amino (Cyclohexyl) methane, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, 3-methylheptamethylenediamine, 4,4-dimethylheptamethylenediamine, 2,11-diaminododecane, 1,2 -Bis (3-aminopropoxy) ethane, 2,2-dimethyl Rupropylenediamine, 3-methoxy-hexamethylenediamine, 2,5-dimethylhexamethylenediamine, 5-methylnonamethylenediamine, 5-methylnonamethylenediamine, 1,4-diaminocyclohexane, 1,12-diaminooctadecane, 2 , 5-Diamino-1,3,4-oxadiazole, 2,2-bis (4-aminophenyl) hexafluoropropane, N- (3-aminophenyl) -4-aminobenzamide, 4-aminophenyl-3 -Aminobenzoate, 6-amino-2- (p-aminophenyl) benzimidazole and the like are used alone or as a mixture of two or more, and preferably 4,4'-diaminodiphenyl ether is used alone.

  A polymerization catalyst is not necessarily required for the polycondensation reaction between the two carried out at a molar ratio of 1: 1, but tertiary amines can be used to control the reactivity. Tertiary amines include, for example, trimethylamine, triethylamine, pyridine, isoquinoline, 2-ethylpyridine, 2-methylpyridine, N-ethylmorpholine, N-methylmorpholine, N, N-diethylcyclohexylamine, N, N -Dimethylcyclohexylamine, 4-benzoylpyridine, 2,4-lutidine, 2,6-lutidine, 2,4,6-collidine, 3,4-lutidine, 3,5-lutidine, 4-methylpyridine, 3-methyl Examples include pyridine, 4-isopropylpyridine, N, N-dimethylbenzylamine, 4-benzylpyridine, N, N-dimethyldodecylamine and the like.

  The polycondensation reaction can be carried out using organic solvents such as N, N-dimethylformamide, N, N-dimethylacetamide, N, N-diethylformamide, N, N-diethylacetamide, N-dimethylmethoxyacetamide, N-methylcaprolactam, dimethyl sulfoxide. N-methyl-2-pyrrolidone, tetramethylurea, pyridine, dimethylsulfone, hexamethylphosphoramide, tetramethylenesulfone, formamide, N-methylformamide, butyrolactone, etc. are used alone or as a mixture of two or more. . These organic solvents can also be used in combination with solvents having poor solvent properties such as benzene, toluene, xylene, cyclohexane, benzonitrile and dioxane.

  The primary product of the polycondensation reaction is a polyamic acid that is a precursor of a polyimide resin, and this amic acid solution (which may be the reaction product solution itself) is applied on a metal foil using a coating device. Apply to. As the coating apparatus, a gravure coater, a reverse roll coater, a bar reverse roll coater, a bar coater, a doctor blade coater, a curtain flow coater, a die coater, a multilayer die coater, and the like can be used. The polyamic acid solution can also be applied so as to have multiple layers. Or the polyimide resin film can be produced from polyamic acid and the method of sticking this on metal foil using an adhesive agent can also be taken.

In the fine pitch application, a method of directly bonding a polyimide resin to a metal foil without using an adhesive is used. Polyimide resins showing good adhesion to such metal foils as copper foil include (A) isopropylidenebis (4-phenyleneoxy-4-phthalic acid) dianhydride and (B) 3,3 ′, 4 Is a copolymer of two aromatic tetracarboxylic dianhydrides consisting of 4,4'-benzophenonetetracarboxylic dianhydride and (C) 6-amino-2- (p-aminophenyl) benzimidazole Resin etc. are mentioned.
WO 01/29136 A1

Moreover, it can also be made to adhere directly to metal foil using the polyimide resin synthesize | combined via a polyamic acid, without using an adhesive agent, The following are mentioned as this polyimide resin.
・ Two types of tetracarboxylic dianhydrides consisting of (A) pyromellitic dianhydride and (B) 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride and (C) 6-amino- Copolymer with 2- (p-aminophenyl) benzimidazole, (A) isopropylpyridenebis (4-phenyleneoxy-4-phthalic acid) dianhydride and (B) 3,3 ′, 4,4 ′ Copolymers of two types of tetracarboxylic dianhydrides consisting of 2-biphenyltetracarboxylic dianhydride and (C) 6-amino-2- (p-aminophenyl) benzimidazole, (A) isopropylpyridenebis Two tetracarboxylic dianhydrides consisting of (4-phenyleneoxy-4-phthalic acid) dianhydride and (B) 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and (C) At least one of 6-amino-2- (p-aminophenyl) benzimidazole and (D) bis (4-aminophenyl) ether (D ₁ ) and phenylenediamine (D ₂ ) Copolymers with two or three types of diamines

  On such a polyimide resin layer having good adhesion to the metal foil, it is also possible to coat a polyimide resin having low hygroscopicity or low thermal expansion or polyamic acid which is a precursor thereof. Examples of the polyimide resin synthesized via polyamic acid include those described above.

  In addition, a method in which a thermoplastic polyimide resin is brought into contact with a metal foil and a double-sided metal foil polyimide resin laminate is formed by thermal fusion is industrialized, and such a method is also applicable. The present invention can be applied to other methods as long as a laminate of a metal foil and a polyimide resin is obtained.

  In this case, for the purpose of controlling the linear expansion coefficient, adjusting the mechanical characteristics, improving the adhesion, etc., it is possible to use a blend of different polyimide resins or a blend of different resins. In addition, for the purpose of improving various properties, inorganic, organic or metallic powders, fibers, etc. can be mixed and used, and an antioxidant is added to prevent oxidation of the metal foil conductor, or adhesion A silane coupling agent or the like can be added for the purpose of improving the property.

  After producing a metal foil / resin layer laminate, preferably a copper foil / polyimide resin layer laminate (polyimide resin copper clad plate) by any of these methods, the resin layer is about 5 to 50 ° C. above the glass transition point Tg. Preferably, the heat treatment is performed at a temperature lower by about 10 to 30 ° C. in a nitrogen atmosphere for at least about 8 hours. At this time, the copper-clad plate may be in the form of a roll or a single sheet, but in view of mass productivity, heat treatment in the form of a roll is preferred. A similar effect can be obtained by using a vacuum oven instead of the inert gas atmosphere, but it is appropriate to use an inert gas oven in consideration of the heat transfer rate.

  In order to increase the heat transfer efficiency, the time for the entire product to reach the set temperature can be shortened by introducing an auxiliary heater to the column supporting the roll. If the heat treatment time is too long, the elongation at break may decrease. However, by differential thermal analysis (DSC) measurement after heat treatment, an endothermic peak appears in the Tg temperature range at the glass transition point when the temperature is raised at a rate of 10 ° C / min. This is done until If the treatment is performed at a temperature close to the glass transition point Tg, a stable structure may not be obtained. As a result of heat treatment, when the heat value of the endothermic peak occurring in the glass transition point Tg temperature region is observed at 0.5 J / g or more per unit weight of the resin at the time of temperature rise by DSC measurement, the effect of dimensional stabilization can be confirmed.

  The necessary heat treatment temperature and heat treatment time, which are the heat treatment conditions, depend on the type of resin, but the heat treatment time is generally about 8 hours or longer, preferably about 24 to 120 hours. A heat treatment time longer than this is costly, which is industrially impractical, and thermal decomposition of the resin cannot be ignored. However, when the thermal decomposition of the resin is hardly observed, the longer the processing time, the better.

  When the resin is composed of a large number of components, for example, the resin layer is a blend or a multilayer structure, which corresponds to this, but only the main component of the resin is physically aged. There are some cases where an effect can be obtained. In addition, when the glass transition points Tg of the resins are substantially equal, the dimensional stabilization effect is large. Further, multi-stage heat treatment is also effective in which heat treatment is performed in accordance with the glass transition point Tg of the higher constituent resin, and subsequently heat treatment is performed at a temperature lower than the glass transition point Tg.

  After the heat treatment is completed, the dimension of the laminate is measured as a reference value. The measurement was carried out by holding a laminate sheet of 200 × 250 mm size in a constant temperature and humidity chamber at 20 ° C. and 65% RH for 24 hours, then drilling a total of 20 holes with a diameter of 1 mm at 50 mm intervals in the laminate sheet, This is done by measuring the distance between the centers of the holes. The dimension measured in the coating direction is defined as the MD direction, and the dimension measured in the direction perpendicular to the coating direction is defined as the TD direction.

  After that, copper etching is performed using a surface treatment apparatus such as an etcher, and the dimensions are measured in the same manner after being kept in a constant temperature and humidity chamber at 20 ° C. and 65% RH for 24 hours. Next, after heating at 200 ° C. for 30 minutes and holding in a constant temperature and humidity chamber at 20 ° C. and 65% RH for 24 hours, the dimensions are measured in the same manner. When designing a product, the problem of dimensional variation after heating is important. When the terminal pitch is 40 μm or less, the value of 3σ is preferably 0.05% or less when the standard deviation σ is used.

  In the present invention, it can be used in combination with other dimensional stabilization methods. In other words, when the dimensional stability (heat shrinkage rate and its variation) obtained by other methods is slightly insufficient for the specifications, the structural stability by physical aging can be easily achieved, so that the desired dimensional stability can be easily achieved. Obtainable.

  In particular, after purchasing a commercially available copper-clad plate, heat treatment is performed at a temperature about 10 ° C. lower than the glass transition point Tg measured by DSC, and heat treatment is performed so that an endothermic peak occurs near the glass transition point Tg during DSC temperature rise measurement. , Variation in dimensional stability is suppressed.

  As a result of heat treatment, if the heat quantity of the endothermic peak that appears near the glass transition point Tg shows a value of 0.5 J / g or more per unit weight of the resin, preferably 2.0 J / g or more, the dimensional stability and the effect of reducing the variation are clear. Can be confirmed. However, if a product that has been dimensionally stabilized by heat treatment is exposed to a temperature above the glass transition point, the dimension stabilizing effect is lost.

  The calorific value (endothermic amount) ΔH of this endothermic peak is measured as a differential thermal analysis (DSC) conducted in an inert gas under conditions of a heating rate of 10 ° C./min. At this time, the glass transition point Tg temperature The base line for calculating the peak area of the endothermic peak observed in the region is used by extending the base line on the high temperature side to the glass transition point Tg temperature region and surrounded by the intersection with the DSC curve at the glass transition point Tg. It is calculated from the peak derived from the volume relaxation phenomenon. The DSC measurement sample is measured with a metal foil attached, and the weight of the resin layer is converted from the difference in weight before and after etching.

  Next, the present invention will be described with reference to examples.

Example 1
For a copper-clad plate (Nippon Steel Chemicals Espanex KE), the glass transition temperature Tg was measured by DSC at a heating rate of 10 ° C./min in a nitrogen stream, and it was 345 ° C. When this roll-shaped copper-clad plate was heat-treated at 330 ° C. for 72 hours in a nitrogen atmosphere, the endothermic enthalpy observed at the glass transition point after the heat treatment was 0.55 J / g. The weight ratio of copper to resin was determined from the weight ratio before and after etching and was converted to a value per unit weight of the resin.

After the heat treatment, the obtained copper-clad plate was cut into a sheet, and the endothermic amount ΔH at the glass transition temperature and the cumulative dimensional change rate (total shrinkage) were measured, and the average value and the dispersion value 3σ were calculated. The sample was subjected to measurement without removing the copper foil, and the dry weight after the copper was removed by etching after the measurement was taken as the weight of the resin.
ΔH: DSC7 manufactured by PerkinElmer was used, and DSC measurement was performed at a heating rate of 10 ° C / min. At this time, the baseline for calculating the peak area of the endothermic peak observed in the glass transition temperature Tg temperature range is , The base line on the high temperature side is extended to the glass transition temperature Tg temperature region, and the total heat shrinkage calculated from the peak derived from the volume relaxation phenomenon surrounded by the intersection with the DSC curve at the glass transition temperature Tg: IPC -TM-650 2.2.4 Revision C (Method C)
However, the rate of change when the exposure temperature is changed to 200 ° C

Comparative Example 1
In Example 1, the total heat shrinkage at 200 ° C. of the copper clad plate before heat treatment was measured.

Example 2
For a copper-clad polyimide film (Kanesu Chemical Product Apical NPI), the glass transition temperature Tg was measured by DSC at a heating rate of 10 ° C./min in a nitrogen stream to be 348 ° C. When this roll-shaped copper clad sheet was heat-treated at 330 ° C. for 72 hours in a nitrogen atmosphere, the endothermic enthalpy observed at the glass transition point after the heat treatment was 0.61 J / g. The weight ratio of copper to resin was determined from the weight ratio before and after etching and was converted to a value per unit weight of the resin. The total heat shrinkage at 200 ° C. after the heat treatment under this nitrogen atmosphere was measured.

Comparative Example 2
In Example 2, the total heat shrinkage at 200 ° C. of the copper clad plate before heat treatment was measured.
The results obtained in the above examples and comparative examples are shown in the following Table 1.
Table 1
ΔH Measurement total shrinkage (%)
Heat treatment condition (J / g) direction average 3 σ
Example 1 0.55 TD -0.02 0.02
330 ° C (Tg-15 ° C), 72h MD -0.03 0.02
Comparative Example 1 0.0 TD -0.05 0.03
(Unprocessed) MD -0.06 0.04
Example 2 0.61 TD -0.00 0.03
330 ° C (Tg-18 ° C), 72h MD -0.00 0.03
Comparative Example 2 0.0 TD -0.04 0.06
(Unprocessed) MD -0.04 0.06

Example 3
Isopropylidenebis (4-phenyleneoxy-4-phthalic acid) dianhydride (molar ratio 0.4), 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride (molar ratio 0.6) and 6-amino- Using a roll coater, N-methyl-2-pyrrolidone varnish solution of polyimide resin (polymer solid content concentration 14% by weight) obtained by copolymerizing 2- (p-aminophenyl) benzimidazole (molar ratio 1.00) The coating was applied to a thickness of 1/2 mil (12.7 μm) on a 1/2 ounce (18 μm) copper foil.

  This copper foil / polyimide resin (Tg 305 ° C.) laminate was dried at a maximum temperature of 390 ° C. in an environment with an oxygen concentration of 0.5% or less. The solvent content after drying was 0.4% by weight. After slow cooling, the wound roll was put into a nitrogen oven, and heat treatment was performed by changing the treatment time and temperature in various ways.

  After the heat treatment, the obtained copper-clad plate was cut into a sheet shape, and the endothermic amount ΔH at the glass transition temperature was measured in the same manner as in Example 1.

  The results obtained in Example 3 are shown in the graph of FIG. From this graph, it is shown that the endothermic amount ΔH at the glass transition temperature clearly increases in a shorter time as the processing temperature is closer to Tg, and in order to perform heat treatment in a realistic time, it is about Tg-15 ° C Has been shown to be desirable.

It is a graph which shows the relationship between (DELTA) H in Example 3, and heat processing temperature and time. It is a conceptual sectional view showing a state where an IC is mounted on an FPC.

Explanation of symbols

1 Resin layer (base film)
2 FPC
3 terminal 4 bump 5 IC

Claims (2)

It is a laminate of a metal foil and a resin layer made of a polyimide resin having a glass transition point Tg of 290 to 350 ° C., when glass is subjected to differential thermal analysis in an inert gas at a heating rate of 10 ° C./min. A flexible metal foil laminate in which the heat value of the endothermic peak observed in the transition region shows a value of 0.5 J / g or more per unit weight of the resin. The flexible metal foil laminate according to claim 1, which is a laminate of a metal foil and a resin layer, and is heat-treated at a temperature 5 to 50 ° C lower than the glass transition point Tg of the resin for 8 hours or more .

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