JP3514668B2 - Coverlay film - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coverlay film for protecting a surface of a flexible printed wiring board or the like for protecting a conductor circuit.

[0002]

2. Description of the Related Art A printed circuit board such as a flexible printed circuit board has a surface on which a precisely designed conductor circuit is formed by a printing method to protect the conductor circuit from insulation, rust prevention, damage prevention, etc. Is covered with a cover lay film.

There are two types of cover lay films, an adhesive type and a non-adhesive type. The adhesive types include polyimide (PI) and polyethylene terephthalate (PE).
It is commercially available as a thin and flexible film in which an acrylic or epoxy semi-curing type adhesive is applied to one surface of the film T) and a release film is attached thereon.

Thermoplastic PI is used for the adhesiveless type. There are two possible processes for covering the surface of the printed wiring board with the coverlay film, one of which is to make a hole in the coverlay film with an NC drill and then to cover the FPC substrate. Method and
The other is a method in which a coverlay film is coated on a substrate and then perforated with a laser. The former method has a large minimum hole diameter and has problems in hole processing accuracy and position accuracy, and is a method that cannot be applied to high density type.

Since the adhesive type coverlay film uses an adhesive in a semi-cured state, sufficient storage management is required. Moreover, since the heat resistance of the adhesive itself is poor, the solder heat resistance is poor. Further, in the case of a non-adhesive type thermoplastic polyimide cover lay film, it is necessary to press at a high temperature close to 300 ° C. when covering the substrate, so that a general-purpose pressing machine cannot be used.

[0006]

As described above, applying the adhesive to one surface of the coverlay film is a factor that increases the number of steps of manufacturing the coverlay film and increases the manufacturing cost. Also, if an adhesive with low heat resistance that is adhesively hardened at a relatively low temperature and low pressure is used, sufficient heat resistance cannot be obtained. Conversely, an adhesive with good heat resistance can only be covered with a cover layer under high temperature and high pressure conditions. There is a problem that it is difficult to bond the film.

Therefore, the object of the present invention is to solve the above-mentioned problems, to have excellent heat resistance, and to exhibit good adhesiveness to a printed wiring board under a heating condition at a low temperature of 260 ° C. or lower, that is, at a low temperature and a short time. It is an object of the present invention to provide a coverlay film for protecting a conductor circuit of a printed wiring board, which has a good insulating property and can be adhered efficiently in time.

[0008]

In order to solve the above problems, according to the present invention, a coverlay film for protecting a conductor circuit of a printed wiring board has a crystal melting peak temperature of 260 ° C. or higher. Of 65 to 35% by weight of the polyarylketone resin and 35 to 65% by weight of the amorphous polyetherimide resin. The thermoplastic resin composition is obtained by differential scanning calorimetry. The glass transition temperature measured when heated is 150 to 230 ° C., and the relationship between the heat of crystal fusion ΔHm and the heat of crystallization ΔHc generated by crystallization during temperature rise satisfies the relationship represented by the following formula (I). It was a coverlay film.

Formula (I): [(ΔHm−ΔHc) / ΔHm] ≦ 0.5 In the coverlay film of the present invention described above, the thermoplastic resin constituting the coverlay film has a glass transition temperature of 150 to 230 ° C. , And the relationship between the heat of crystal fusion ΔHm and the heat of crystallization ΔHc generated by crystallization during heating is expressed by the above formula (I).
The elastic modulus of the thermoplastic resin is appropriately reduced under the condition of a relatively low temperature of 250 ° C. or less during heat fusion by heating and pressurization, so that the fine wiring pitch of the conductor circuit can be satisfied. Is a coverlay film that is reliably filled with a thermoplastic resin and has extremely high electrical insulation reliability.

Further, since the thermoplastic resin composition appropriately advances the crystallinity of the polyarylketone resin by heating during heat fusion, the thermoplastic resin composition surely exhibits a heat resistance of 260 ° C. or more and a sufficient insulating property. And has excellent mechanical strength and electrical insulation, and forms an excellent protective layer.

Since the above-mentioned thermoplastic resin composition has a large adhesive strength with a conductor foil made of metal, a printed wiring board such as a flexible printed wiring board having a conductor circuit made of the conductor foil on the surface thereof and a printed wiring board superposed thereon. The coverlay film is firmly adhered. Normally, a conductor foil made of metal, such as a surface-roughened copper foil, whose surface is roughened, is used, but an adherend with a roughened surface is more bonded than an adherend without a roughened surface. Strength increases.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The polyarylketone resin which is the first component constituting the coverlay film in the present invention is a thermoplastic resin containing an aromatic nucleus bond, an ether bond and a ketone bond in its structural unit, that is, , A heat-resistant crystalline polymer composed of a combination structure of phenyl ketone and phenyl ether.

Typical examples of the polyarylketone resin include polyetherketone, polyetheretherketone, polyetherketoneketone, etc. In the present invention, the polyetheretherketone represented by the following chemical formula 1 is It can be used as a suitable one.

[0014]

[Chemical 1]

The amorphous polyetherimide resin which is the second component of the coverlay film is an amorphous thermoplastic resin containing an aromatic nucleus bond, an ether bond and an imide bond in its structural unit. In, the polyether imide resin represented by the following chemical formula 2 can be applied.

[0016]

[Chemical 2]

The coverlay film is composed of a composition obtained by blending the above two kinds of heat resistant resins in a predetermined ratio, that is, the thermoplastic resin composition is a polyaryl having a crystal melting peak temperature of 260 ° C. or higher. Ketone resin 6
5-35 wt% and amorphous polyetherimide resin 35-
It has a glass transition temperature of 150 to 230 ° C. when it is heated by differential scanning calorimetry.

The reason for limiting the above blending ratio is that the polyarylketone resin is blended in a large amount exceeding 65% by weight, or the polyetherimide resin is blended in a small amount less than 35% by weight. The crystallinity of the circuit board becomes too high and its crystallinity becomes too high, which makes it difficult to adhere to the surface of the printed wiring board due to heat fusion, and the volume shrinkage (dimensional change) accompanying crystallization becomes large, resulting in a circuit board. This reduces the reliability of.

If the amount of the crystalline polyallyl ether ketone resin is less than 35% by weight or the amount of the amorphous polyetherimide resin exceeds 65% by weight, the crystallization rate of the composition becomes too slow and the crystallinity of the composition becomes low. Is low and the heat resistance is low, which is not preferable.

The thermal characteristics of the coverlay film before heat fusion, which is an important control factor in the present invention, are the heat of crystal fusion ΔHm and the heat of crystallization ΔH generated by crystallization during heating.
The relation with c satisfies the relation represented by the following formula (I).

The thermal characteristics represented by the formula (I): [(ΔHm−ΔHc) / ΔHm] ≦ 0.5 (ΔHm−ΔHc) / ΔHm are JI
Measured values of two transition heats appearing in the DSC curve when the temperature is raised by differential scanning calorimetry according to SK 7121 and JIS K7122, heat of fusion of crystal ΔHm (J / g) and heat of crystallization ΔHc (J / g) It is calculated from the value of.

Although the value of the formula represented by (ΔHm-ΔHc) / ΔHm depends on the kind and molecular weight of the raw material polymer and the compounding ratio of the composition, it greatly affects the molding and processing conditions of the coverlay film. . That is, when the coverlay film is formed, the raw polymer is melted and then rapidly cooled, whereby the value of the above formula can be reduced. Further, these numerical values can be controlled by adjusting the thermal history applied in each step. The heat history as used herein refers to the temperature of the coverlay film and the time during which the temperature has been maintained. The higher the temperature, the larger this numerical value tends to be.

Regarding the thermal characteristics of the coverlay film before heat fusion, it is preferable that the value shown on the right side of the above formula (I) is as small as possible because the adhesiveness is good. The more preferable value on the right side of the formula (I) is 0.35 or less.

The thermal characteristics of the cover-lay film after heat-sealing preferably satisfy the relationship of the following formula (II).

Formula (II): [(ΔHm−ΔHc) / ΔHm] ≧ 0.
7 When the value of the above formula (II) is a low value of less than 0.7, the crystallization of the thermoplastic resin composition is insufficient, and it is particularly difficult to sufficiently exhibit the heat resistance of 260 ° C or higher.

In this way, the thermoplastic resin composition is heated to near the crystal melting peak temperature (Tc) so as to be surely heat-sealed and insulated from the surface of the conductor circuit of the printed wiring board, and the thermoplastic resin composition. Since the composition is crystallized, a printed wiring board having excellent heat resistance can be manufactured.

The coverlay film used in this invention is
The thickness is not particularly limited and can be set according to the bonding application of the adherend, and includes, for example, a film having a thickness of about 5 to 300 μm.

As the method for producing the coverlay film, a well-known method such as an extrusion casting method using a T die or a calendar method may be adopted. From the viewpoint of film forming property and stable productivity, it is preferable to adopt the extrusion casting method using a T die. The molding temperature of the extrusion casting method is appropriately adjusted depending on the flow characteristics and film forming characteristics of the composition, but is generally above the melting point of the composition and below 430 ° C.

The thermoplastic resin composition constituting the coverlay film used in the present invention may be blended with a resin other than the main component and other additives to such an extent that the effects of the present invention are not impaired. Specific examples of the additive include a heat stabilizer, an ultraviolet absorber, a light stabilizer, a colorant, a lubricant, a flame retardant, and an inorganic filler. In addition, the surface of the coverlay film may be subjected to embossing or corona treatment for improving handleability.

The printed wiring board to which the coverlay film of the present invention is adhered is usually applicable to a flexible printed wiring board, but if necessary, the base material of the insulating layer and the type of resin are not particularly limited. It can be used, for example, a glass cloth base epoxy resin, a paper base epoxy resin, a glass cloth base polyimide resin, or a printed wiring board having an insulating layer made of a known material can be coated.

[0031]

Examples and Comparative Examples Examples 1 to 3 of the coverlay film of the present invention and Comparative Example 1 for comparison therewith,
2 will be described below.

Example 1 Polyetheretherketone resin (PEEK381G manufactured by Victrex Co.) (PEEK381G in the following text or in Tables 1 and 2) 60 wt% and a polyetherimide resin (General Electric) (Manufactured by Ultem-1000) (abbreviated as PEI in the following text or in Tables 1 and 2).
40 wt% was melt mixed. This mixed composition was extruded to produce a coverlay film having a thickness of 25 μm.

[Example 2] In Example 1, the blending ratio of the mixed composition was 40% by weight of PEEK and 60% by weight of PEI.
A coverlay film was produced in the same manner except that

[Example 3] In Example 1, the blending ratio of the mixed composition was 30% by weight of PEEK and 70% by weight of PEI.
A coverlay film was produced in the same manner except that

[Comparative Examples 1 and 2] In the same manner as in Example 1, except that the mixing ratio of the mixed composition was 100% by weight of PEEK (Comparative Example 1) or 100% by weight of PEI (Comparative Example 2). Of the cover lay film was manufactured.

In order to investigate the physical properties of the coverlay films of the above-mentioned Examples and Comparative Examples, the following items (1) and (2) were measured or calculated values were calculated from the measured values. The results are summarized in Table 1.

(1) Glass transition temperature (° C), crystallization temperature (° C), crystal melting peak temperature (° C) JIS K7121
According to the above, using the sample 10 mg, the above-mentioned respective temperatures when the heating rate was raised at 10 ° C./min using DSC-7 manufactured by Perkin Elmer Co., were obtained from the thermogram.

(2) (ΔHm-ΔHc) / ΔHm According to JIS K7122, 10 mg of a sample was used, and the heating rate was 1 using Perkin Elmer DSC-7.
The heat of crystal fusion ΔHm (J / g) and the heat of crystallization ΔHc (J / g) were determined from the thermogram when the temperature was raised at 0 ° C./min, and the value of the above formula was calculated.

[0039]

[Table 1]

[Coating Test of Flexible Printed Wiring Board] A flexible printed wiring board in which a circuit pattern was formed on a double-sided copper clad laminate of a polyimide resin substrate by a subtractive method and a conductive circuit was formed by etching was used as a test object product. .

Then, a cover lay film 3 (Examples 1 to 3 and Comparative Examples 1 and 2) having a thickness of 25 μm was overlaid on the surface of the printed wiring board, and the temperature was 760 mmHg in a vacuum atmosphere, the pressing temperature was 240 ° C., and the pressing pressure was 30 kg /. Heat fusion was performed under the conditions of cm ² and a pressing time of 20 minutes.

The wraparound state of the resin in the vicinity of the circuit pattern of the obtained flexible printed wiring board with a coverlay film coating was observed with a scanning electron microscope (method (3) below), and the heat resistance was measured as shown in (4) below. ) Test method,
These results are also shown in Table 1.

(3) A flexible printed wiring board covered with a coverlay film was embedded in epoxy resin, a cross-section observation sample was prepared with a precision cutting machine, and the cut surface was observed with a scanning electron microscope (SEM). The presence or absence of delamination between the coverlay film and the copper foil conductive circuit was evaluated.

(4) Heat resistance In accordance with JIS C6481 normal solder heat resistance, 2
Floating in a solder bath at 60 ° C for 10 seconds with the copper foil side of the test piece in contact with the solder bath, taking out of the bath and allowing to cool to room temperature, and visually observing the presence or absence of swelling or peeling points,
The quality was evaluated.

The cover lay film of Comparative Example 1 could not adhere to the flexible printed wiring board at a pressing temperature of 240 ° C. because of its high crystallization rate.

The cover lay film of Comparative Example 2 is
At a pressing temperature of 240 ° C., the adhesiveness was not sufficient, peeling was observed in a part of the layers of the laminate, and the heat resistance was also insufficient.

On the other hand, the cover lay films of Examples 1 to 3 have sufficient adhesiveness at a pressing temperature of 240 ° C. and also undergo crystallization, and have a crystal melting peak temperature of 340 ° C.
It has excellent heat resistance as described above, has no delamination from the conductor circuit of the printed wiring board, and has solder heat resistance.

[0048]

As described above, the coverlay film of the present invention is a coverlay film used for a printed wiring board, which is made of a thermoplastic resin composed of polyarylketone and amorphous polyetherimide showing a predetermined heat resistance. Since such a coverlay film is formed of a resin composition and has a property in which the crystallinity of the polyarylketone resin is appropriately advanced, such a coverlay film is used for a printed wiring board when heated to a low temperature of 260 ° C. or lower. It has properties suitable for bonding to the surface, can be bonded in a relatively short time, and has heat resistance that can withstand 260 ° C after heat fusion, and also has excellent mechanical strength and electrical insulation. It has the advantage of showing.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI C09J 7/02 C09J 7/02 Z (72) Inventor Koichiro Taniguchi 5-8 Mitsuyacho, Nagahama-shi, Shiga Prefecture Mitsubishi Jushi Corporation Nagahama In-plant (72) Inventor Kaoru Nomoto 1-1, Showa-cho, Kariya city, Aichi prefecture, Denso Co., Ltd. (72) Inventor Toshihiro Miyake 1-1-chome, Showa-machi, Kariya city, Aichi prefecture (72) Inventor, Takagaki Takanari 1-chome, Showa-cho, Kariya city, Aichi (DENSO CORPORATION) (56) Reference JP-A-9-277457 (JP, A) JP-A-2-269765 (JP, A) JP-A-5-310951 (JP) , A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) H05K 1/03 H05K 1/05 H05K 3/00 H05K 3/22 H05K 3/28 H05K 3/44 H05K 3/46 C08J 5 / 18 C08L 71/10 C08L 73/00 C08L 79/08

Claims (2)

(57) [Claims] 1. A coverlay film for protecting a conductor circuit of a printed wiring board, the coverlay film comprising:
The thermoplastic resin composition comprises 65 to 35% by weight of a polyarylketone resin having a crystal melting peak temperature of 260 ° C. or higher and 35 to 65% by weight of an amorphous polyetherimide resin. , The glass transition temperature measured by the differential scanning calorimetry is 150 to 2
A cover lay film having a characteristic that the relationship between the heat of crystal fusion ΔHm at 30 ° C. and the heat of crystallization ΔHc generated by crystallization during temperature increase is a characteristic satisfying the relationship represented by the following formula (I). Formula (I): [(ΔHm−ΔHc) / ΔHm] ≦ 0.5 2. The coverlay film according to claim 1, wherein the polyarylketone resin is a polyetheretherketone resin.