JP3227874B2 - Manufacturing method of laminated board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated board used for a printed wiring board.

[0002]

2. Description of the Related Art In recent years, as electronic devices have become smaller and higher in density, components mounted on printed wiring boards have shifted from conventional insertion types to surface mounting types. Also, the surface mounting method is becoming mainstream. Accordingly, various demands have been made on copper-clad laminates used as printed wiring boards. That is, when components such as chips are surface-mounted on a printed wiring board, matching of thermal expansion coefficients becomes a problem from the viewpoint of connection reliability. For example, the thermal expansion coefficient of a thin surface-mount type TSOP (Thin Small Outline Package), which has recently become widely used, is about 5 × 10 ⁻⁶ / ° C. However, the thermal expansion coefficient of a fiber reinforced plastic substrate such as a glass cloth base epoxy resin copper-clad laminate generally widely used as a printed wiring board is about 15 to 17 × 10 ⁻⁶ / ° C. It is very high compared to that of parts. Therefore, when components with a low coefficient of thermal expansion are surface-mounted on a printed wiring board with a high coefficient of thermal expansion, cracks are likely to occur in the solder at the connection due to the large difference in coefficient of thermal expansion. Nature cannot be secured. In order to improve the connection reliability with the chip component, a substrate having a thermal expansion coefficient close to the component to be mounted, that is, a substrate having a low thermal expansion coefficient is required.

[0003]

As the substrate material having a low coefficient of thermal expansion, a ceramic substrate such as alumina or aluminum nitride, invar or 4 different from the above-mentioned organic substrate is used.
A metal core substrate using a low thermal expansion metal such as a two alloy as a core is used. However, looking at these,
Ceramic substrates are so hard that they cannot be machined by drilling or cutting like organic substrates, they are heavier than organic substrates, which is disadvantageous in weight reduction, and they have poor toughness and are easy to break due to poor toughness. There are drawbacks such as bad or complicated circuit processing and multi-layering steps, resulting in high cost. Further, a metal core substrate having a low thermal expansion metal as a core has disadvantages such as being heavy and unable to cope with a reduction in weight, and requiring an insulating coating inside a hole of the metal core when forming a through hole. Therefore, development of a conventional organic substrate having excellent workability and a low coefficient of thermal expansion is desired.

As a low thermal expansion organic substrate, a substrate using a low thermal expansion base material such as quartz fiber or aramid fiber has been studied. However, quartz fibers have not been put to practical use because of their extremely poor machinability and high cost.
On the other hand, aramid fibers have poor machinability like quartz fibers, have low adhesiveness to resin, and are apt to absorb moisture. Recently, nonwoven fabrics have begun to replace cloth in order to improve the machinability of aramid fibers. Although the machinability is improved as compared with the cloth, the problems of adhesiveness to resin and deterioration of characteristics at the time of moisture absorption are still not solved. For these reasons, aramid fiber nonwoven fabrics have not been widely used. As a solution, Japanese Patent Application Laid-Open
A method of impregnating a resin into an aramid fiber non-woven fabric previously treated with a coupling agent as described in JP-A-209836, or improving the reactivity with the resin by activating the surface of the aramid fiber with an acid, alkali treatment or plasma treatment However, at present, sufficient adhesiveness with a resin has not been obtained until practical use is possible.

The present invention has been made in view of such circumstances, and has improved heat resistance during moisture absorption using an aramid fiber nonwoven fabric as a base material, has a low coefficient of thermal expansion, and has connection reliability when a component is surface-mounted. The purpose of the present invention is to provide an excellent substrate.

[0006]

That is, the present invention relates to a method for producing an aramid fiber nonwoven fabric substrate laminate in which a thermosetting resin is impregnated into an aramid fiber nonwoven fabric, dried to form a prepreg, and hot-press molded. The thickness of the sheet after molding is set to be 70% or less of the total thickness of the aramid fiber nonwoven fabric before resin impregnation. Aramid fiber non-woven fabric
A material whose thickness is 70% or less, preferably 50% or less, of the thickness when no pressure is applied by applying pressure is used. That is, a felt-like nonwoven fabric having a low density is used. The volume content of the aramid fiber is preferably at least 40% in order to keep the coefficient of thermal expansion low. Further, when the volume content of aramid fiber is set to 50% or more, the coefficient of thermal expansion becomes 1 × 10 ⁻⁵ / ° C. or less, and high connection reliability with mounting parts that cannot be obtained with a laminate using ordinary glass fiber. It is more preferable since the property can be obtained. Examples of the resin to be impregnated into the aramid fiber nonwoven fabric include a thermosetting resin such as an epoxy resin, a polyimide resin, a phenol resin, a vinyl ester resin, a silicone resin, a melamine resin, and an unsaturated polyester resin, polysulfone, polyetherimide, polyetheretherketone, Although a thermoplastic resin such as polyphenylene oxide can be used, among these, an epoxy resin is most suitable in terms of adhesiveness to aramid fiber and other electrical characteristics.

[0007]

The aramid fiber has a negative coefficient of thermal expansion. On the other hand, the thermal expansion coefficient of the resin is positive. Therefore, the thermal expansion coefficient in the surface direction of the aramid fiber nonwoven fabric base laminate decreases as the volume content of the aramid fibers increases. If the volume content of the aramid fiber is 50% or more, the thermal expansion coefficient is 1 × 10 ^−5.
/ ° C or lower, and high connection reliability with a mounted component that cannot be obtained with a laminate using ordinary glass fibers can be obtained. However, the biggest drawback of the aramid fiber nonwoven fabric base laminate is that it is inferior in solder heat resistance when absorbing moisture. This is attributed to the above-mentioned excellent feature, that is, a low coefficient of thermal expansion in the plane direction. In the conventional aramid fiber nonwoven fabric base laminate, aramid fibers are not uniformly dispersed in the thickness direction. That is, a layer having a high volume ratio of the resin exists between the nonwoven fabrics. The thermal expansion coefficient of a layer having a low aramid fiber volume ratio is much higher than that of a layer having a non-woven fabric having a high aramid fiber volume ratio. A layer having a high thermal expansion coefficient and a layer having a low thermal expansion alternately overlap each other in a conventional aramid fiber nonwoven fabric base laminate. When a rapid temperature change occurs due to a solder heat test or the like, a large thermal stress is generated at the interface between these layers. If it is performed in a state where moisture is absorbed, the water vapor which expands rapidly peels off the interface where the thermal stress is generated in the plate thickness direction, resulting in swelling.

The present invention addresses this drawback. That is, the aramid fiber nonwoven fabric base laminate of the present invention has a layer having a high coefficient of thermal expansion and a layer having a low thermal expansion coefficient in the thickness direction alternately because the aramid fibers are uniformly dispersed in the thickness direction, All layers have the same thermal expansion coefficient in the plane direction. For this reason, there is no interface where a large thermal stress is generated unlike the conventional aramid fiber nonwoven fabric base laminate. In addition, since the density of the nonwoven fabric is low, it is considered that the wettability between the fiber and the resin is improved during the resin impregnation. Therefore, the solder heat resistance during moisture absorption is significantly improved. In the method of the present invention, the plate thickness after hot pressing is made 70% or less, preferably 50% or less of the total thickness of the aramid fiber non-woven fabric before resin impregnation, because the aramid fibers are uniformly dispersed in the plate thickness direction. The purpose of this method is to uniformly disperse aramid fibers in the thickness direction. Hereinafter, the present invention will be described with reference to examples.

[0009]

【Example】

Example 1 Using Teijin's Technora as an aramid fiber,
Thickness 0.3mm, grammage 75g / m ² Was prepared. This was impregnated with epoxy resin and dried to produce a coated cloth.
Was placed and press-molded to obtain an aramid fiber nonwoven fabric base laminate. The thickness of this laminated board was 0.4 mm (excluding copper foil), which was about 33% of the total thickness of the original nonwoven fabric. The aramid fiber volume content of this laminate is 5
0%, and the coefficient of thermal expansion in the plane direction was 8 without copper foil.
× 10 ^-6 / ° C. As a result of cross-section observation, it was found that the aramid fibers were uniformly dispersed in the thickness direction. The results of the soldering heat test after the copper foil of the laminate was removed by etching were good as shown in Table 1, and the 260 ° C after 5 hours of boiling was good.
No abnormality was observed after immersion in the solder bath for 30 seconds.

Example 2 An aramid fiber non-woven fabric was prepared in the same manner as in Example 1 except that the thickness was 0.15 mm and other conditions were the same. This was impregnated and dried with an epoxy resin to prepare a coated cloth, and four of these were further laminated, and a 35-μm-thick copper foil was placed on both sides and press-molded to obtain an aramid fiber nonwoven substrate laminate. The thickness of this laminated board is 0.
4 mm (excluding the copper foil), which was about 67% of the total thickness of the original nonwoven fabric. The aramid fiber volume content of this laminate was 50%, and the thermal expansion coefficient in the plane direction was 8 × 10 ⁻⁶ / ° C. without a copper foil. As a result of cross-sectional observation, it was found that the particles were uniformly dispersed in the thickness direction. The results of the soldering heat test after removing the copper foil of this laminated board by etching are good as shown in Table 1, and the results were 26 hours after boiling for 3 hours.
No abnormality was observed after immersion in the 0 ° C. solder bath for 30 seconds.

Comparative Example 1 An aramid fiber nonwoven fabric was prepared in the same manner as in Example 1 except that the thickness was 0.1 mm and the other conditions were the same. This was impregnated and dried with an epoxy resin to prepare a coated cloth, and four of these were further laminated, and a 35-μm-thick copper foil was placed on both sides and press-molded to obtain an aramid fiber nonwoven fabric base laminate. The thickness of this laminate is 0.4
mm (excluding the copper foil), and the plate thickness was about 100% of the total thickness of the original nonwoven fabric. The aramid fiber volume content of this laminate was 50%, and the thermal expansion coefficient in the plane direction was 8 × 10 ⁻⁶ / ° C. without a copper foil. As a result of the cross-sectional observation, it was found that there was a relatively thin layer having a small amount of aramid fibers between layers having many aramid fibers, and the layer was uniformly dispersed in the thickness direction. Table 1 shows the results of the soldering heat test after the copper foil of the laminate was removed by etching. 26 hours after boiling
Immediately upon immersion in a 0 ° C. solder bath, blistering occurred.

[0012]

[Table 1]

[0013]

As described above, according to the present invention, in the laminate having the aramid non-woven fabric as the base material, the thermal shock resistance such as the solder heat resistance, which has been the biggest problem so far, and particularly when the moisture absorption is performed. Properties can be improved. Thereby, the feature of the low thermal expansion coefficient of the aramid fiber can be fully utilized. Therefore, the laminated board of the present invention and its manufacturing method are very effective as a low-thermal-expansion substrate required for further miniaturization, high-density, or bare chip of a semiconductor element package which will be further advanced in the future.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI B29L 31:34 B29L 31:34 (72) Inventor Yutaka Yamaguchi 1500 Oji Ogawa, Shimodate-shi, Ibaraki Pref. (56) References JP-A-1-257388 (JP, A) JP-A-56-118852 (JP, A) JP-A-2-67332 (JP, A) JP-A-3-62994 (JP, A) JP-A-5-251862 (JP, A) JP-A-6-237055 (JP, A) JP-A-8-224832 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 43 / 18-43/20 B29C 43/32-43/36 B29C 70/06 B32B 15/08 C08J 5/24 H05K 1/03

Claims (3)

(57) [Claims] An aramid fiber nonwoven fabric is impregnated with a resin, dried to form a prepreg, and a plurality of the prepregs are stacked and hot-pressed. A method for producing a laminate, characterized in that the total thickness is not more than 70% of the thickness of the aramid fiber nonwoven fabric. 2. The method according to claim 1, wherein the resin is an epoxy resin. 3. The method according to claim 1, wherein the volume content of the aramid fiber is 40% or more.