JPH0688282B2 - Method for manufacturing multilayer printed wiring board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Object of the Invention" (Field of Industrial Application) The present invention is directed to a multilayer printed wiring board having a good drill smear and a good inner wall roughness without causing axial deviation of the drill when drilling a small diameter drill hole. It relates to a manufacturing method.

(Prior Art) In the field of industrial electronic equipment, the density of wiring is rapidly increasing, and recently, due to the improvement in the integration degree of LSI, the package has been changed from the conventional dual-in-line type package to a multi-terminal type. It has changed to a flat pack type package and the wiring density has become extremely high. Unlike the conventional printed wiring board for dual-in-line package mounting, the printed wiring board for mounting the flat pack type package does not require the lead of the component to be inserted into the through hole, so it should be a small diameter through hole. Therefore, the wiring density is increased.

The small-diameter drilling process required to make a small-diameter through hole requires drill smearing and drilling with good inner wall roughness, but a thick glass cloth such as the conventional 7628 type is used for copper foil. In the multilayer printed wiring board placed immediately below, the surface of the copper foil was rough, causing axial deviation of the drill, resulting in problems such as drill smear and inner wall roughness.

In order to solve this problem, a method of smoothing the copper foil surface and improving drill workability by placing one or more thin glass cloths with a thickness of 0.1 mm or less in contact with the copper foil is provided. is there. However, the thickness used in this method is 0.1mm
The following thin glass cloth is more expensive than the thick 7628 type glass cloth, and it cannot be said that the surface of the copper foil is sufficiently smoothed. There was a flaw that caused it.

There is also a method of using a copper foil with an adhesive to improve the appearance, but there is a drawback that the frequency of drill smear is increased due to an increase in the amount of resin in the adhesive, which leads to an increase in the cost of the copper foil.

(Problems to be Solved by the Invention) The present invention has been made in order to solve the above-mentioned drawbacks, without using an expensive thin glass cloth and without using an adhesive-attached copper foil. An object of the present invention is to provide a multilayer printed wiring board which has a smooth surface, has little axial deviation of the drill and drill smear when drilling a small diameter, and has good inner wall roughness.

[Structure of Invention] (Means and Actions for Solving Problems) As a result of intensive studies to achieve the above-mentioned object, the present inventors have found that a thermoplastic film having a thickness of 50 to 150 μm and a cellulose fiber are used. By interposing a cushion material that becomes between the hot platen and the stainless steel plate, the copper foil surface is smoothed,
The present invention has been completed by finding that a multilayer printed wiring board having a small inner shaft roughness and a drill smear and a good inner wall roughness when a small-diameter drill is processed can be obtained.

That is, the present invention is a method for producing a multilayer printed wiring board in which a prepreg and a copper foil are superposed on both surfaces of an inner layer board, sandwiched between stainless steel boards, and inserted between hot plates via a cushioning material, and integrally molded by heating and pressing. In the method, a cushioning material composed of a thermoplastic film having a thickness of 50 to 150 μm and a cellulose fiber is used, which is a method for producing a multilayer printed wiring board. Also,
The melting temperature of the thermoplastic film is the melting temperature of the prepreg ±
30 ℃ (100 ~ 1 for most epoxy resin prepregs)
It is a method for manufacturing a multilayer printed wiring board at 50 ° C.

The inner layer plate used in the present invention may be two or more layers that are usually used, and the materials (circuit materials, resins, base materials) and manufacturing methods used are not particularly limited, and any It can also be used as an inner layer plate.

The prepreg used in the present invention may be made of glass cloth impregnated with a thermosetting resin, coated and dried. The glass cloth used here has a thickness of
The effect of the present invention can be obtained even with a thin film having a thickness of 100 μm or less, but the effect is remarkable in the case of a thick glass cloth having a thickness of more than 100 μm, for example, 7628 type (thickness 180 μm).
Examples of the thermosetting resin used include epoxy resin, polyimide resin, and modified resins thereof,
These may be used alone or in admixture of two or more.

The copper foil used in the present invention is not particularly limited and may be any, but not too thick in terms of cost and appearance,
Moreover, it is desirable that the adhesive is not attached.

The thermoplastic film used in the present invention may be one that satisfies the following conditions. The first condition is that the thickness is 50 ~
It is within the range of 150 μm. 50μ thick
When it is less than m, the cushioning property is not effective and the appearance is not smoothly finished, which is not preferable. If it exceeds 150 μm, the cushioning property is good and the appearance is smooth, but the cost is high, which is not preferable. Preferably its cushioning properties,
From the viewpoint of cost, the thickness of 80 to 120 μm is preferable. This thermoplastic film is used as a cushioning material by alternately combining it with cellulose fibers. The number of thermoplastic films is preferably 1 to 6, and preferably 1 to 3. Alternating combinations of thermoplastic film and cellulosic fibers,
Cellulose-based fibers may be arranged on the outside as a cushioning material such as film / fiber / film and film / fiber / film / fiber / film.

The second condition is that the melting temperature is preferably the melting temperature of the prepreg used ± 30 ° C, preferably ± 10 ° C. If this difference exceeds ± 30 ° C., the predetermined effect cannot be obtained, and the molded product is liable to slip and molding is dangerous, which is not preferable. Any thermoplastic film may be used as long as it satisfies these two conditions. Specific examples thereof include biaxially stretched OPP film (polypropylene film), polyethylene film, polyester film, polystyrene film, polyvinylidene chloride film and the like, and these can be preferably used.

By using a thermoplastic film whose thickness is 50 to 150 μm and whose melting temperature is within ± 30 ° C of the melting temperature of the prepreg used, it is pressed under an effective cushioning effect and the surface of the copper foil is smoothed. It is what is converted. This method for producing a multilayer printed wiring board can be carried out very easily because the thermoplastic film is simply added between the hot platen and the stainless steel plate in the usual production method.

(Examples) Next, the present invention will be specifically described with reference to Examples.

Example 1 A 7628 type flame-retardant epoxy resin used for FR-4 was formed on the upper and lower sides of an inner layer board whose surface was blackened by forming a circuit with a copper foil having a thickness of 70 μm on a base material having a thickness of 0.4 t. Glass impregnated, coated and dried, 3 pieces of each prepreg A with 40 to 45% by weight of resin is laminated, and 18 μm thick copper foil without adhesive is laminated on top and bottom of this. Clap into a stainless steel plate. Furthermore, cushioning material (fiber / film / fiber) in which 1 sheet of linter paper is placed on the top and bottom of a biaxially oriented polypropylene film (OPP film) with a thickness of 80 μm, is placed on the top and bottom of the stainless steel plate and inserted between the heating plates, and heated. A multilayer printed wiring board molded integrally by pressure lamination was manufactured.

Example 2 In place of the cushion material in which one linter paper is arranged on each of the upper and lower sides of an OPP film having a thickness of 80 μm in Example 1,
Example 1 except that a cushioning material (fiber / film / fiber / film / fiber) obtained by alternately combining two 80 μm-thick OPP films and three linter papers was used.
A multilayer printed wiring board was manufactured in the same manner as in.

Comparative Example 1 Instead of the cushion material used in Example 1,
Except for using a cushioning material consisting of 6 sheets of linter paper,
A multilayer printed wiring board was manufactured in the same manner as in Example 1.

Comparative Example 2 In Comparative Example 1, instead of the inner layer plate having a circuit formed of a copper foil having a thickness of 70 μm on the base material having a thickness of 0.4 t and subjected to surface blackening treatment, and three prepregs A stacked above and below each of the inner layer plate, An inner layer plate with a circuit formed of 70 μm thick copper foil on a 0.5 t thick base material and surface blackened, two prepregs A each above and below and a flame retardant resin for FR-4 216 type glass A multi-layer printed wiring board was manufactured in the same manner as Comparative Example 1 except that the cloth was impregnated, coated, dried, and prepreg B having a resin adhesion amount of 40 to 45% by weight was superposed on the prepreg A one by one. did.

Comparative Example 3 In Comparative Example 1, instead of the 18 μm-thick unadhesive-coated copper foil, an 18 μm-thick copper foil was coated with the same resin as that used for impregnating the prepreg A as an adhesive. A multilayer printed wiring board was manufactured in the same manner as in Comparative Example 1 except that the foil was used.

The drill shaft deviation, inner wall roughness and drill smear were evaluated for the multilayer printed wiring boards manufactured in Examples 1-2 and Comparative Examples 1-3. The evaluation method is to stack three wiring boards and use a drill with a diameter of 0.5 mm to rotate at 70.000 rpm and feed speed.
After drilling 5000 holes at 3 m / min, and through-hole plating, 100
A cross section was performed for each 0 hole, and the drill axial deviation and inner wall roughness were evaluated. Drill smear rating is thickness 18
The following formula was used for a copper foil of μm.

Size of drill smear (%) = length of smear (μm) ×
100/18 (μm) Further, the appearance and cost were also examined, but the appearance was evaluated by visually observing the area where the intersection of the glass cloth on the substrate surface after etching was exposed from the resin surface. When the area is zero ○
Mark, 0 to less than 20% □ mark, 20 to less than 40% △
Mark, when it was less than 40-60%, it was displayed as x mark. In terms of cost, the lowest level is indicated by a circle, the middle level is indicated by a square, and the highest level is indicated by a triangle.

The results of the above evaluations are shown in Table 1. In all cases, the multi-layer printed wiring board according to the present invention showed a remarkable excellent effect.

"Effects of the Invention" As is clear from the above description and Table 1, according to the method for manufacturing a multilayer printed wiring board of the present invention, the surface of the copper foil can be formed without using expensive glass cloth or copper foil. This is industrially advantageous because it can be made smooth, and when a small-diameter drill is processed, there is little axial deviation of the drill, drill smear, and good inner wall roughness.

Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display area B29L 9:00 4F

Claims (2)

[Claims] 1. A method for producing a multi-layer printed wiring board in which a prepreg and a copper foil are superposed on both sides of an inner layer board, sandwiched between stainless steel boards, inserted between hot plates via a cushioning material, and integrally molded under heat and pressure. 3. A method for producing a multilayer printed wiring board, which comprises using a cushioning material composed of a thermoplastic film and a cellulose fiber having a thickness of 50 to 150 μm. 2. The melting temperature of the thermoplastic film is the melting temperature of the prepreg used ± 30 ° C.
A method for manufacturing a multilayer printed wiring board according to item.