JPS59201488A - Printed board - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to the layer structure of a multilayer printed circuit board, and particularly to a printed circuit board on which integrated circuit elements are directly mounted.

(b) Background of the technology It is necessary to directly mount integrated circuit elements on printed circuit boards to achieve high-density mounting of various electronic devices and to miniaturize the devices. The layer structure of the printed circuit board made it impossible to directly mount integrated circuit elements from a reliability standpoint.

FIG. 1 shows the layer structure of a conventional multilayer printed circuit board. A plurality of printed circuit boards a made of an epoxy resin or polyimide resin plate 1 covered with copper foil 2 on one side, a plurality of printed circuit boards b made of an epoxy resin or polyimide resin plate 1 covered with copper foil 2 on both sides, and insulation. Multiple sheets of adhesive C that also serve as layers
are laminated to form a multilayer print I/substrate 3. In each copper foil 2, only the parts necessary for the circuit configuration are left and the other parts are removed, and the layers are connected by through-ball plating.

FIG. 2 is a diagram in which an integrated circuit element is directly mounted on a printed circuit board. There are terminals 5 on the back surface of the ceramic substrate 4 on which the integrated circuit elements are mounted, and terminals 6 corresponding to the terminals 5 on the back surface of the ceramic substrate 4 are also arranged at the positions on the surface of the printed circuit board 3 where the integrated circuit elements are mounted. The terminals 5 and 6 are connected by remelting soldering or the like.

When an integrated circuit element is directly mounted on such a printed circuit board 3, the printed circuit board 3 and the ceramic substrate 4 of the integrated circuit element are
Due to extremely large differences in thermal expansion coefficients (printed circuit board thermal expansion coefficient 1.5 x 10 * ws/Tsuru °C, ceramic thermal expansion coefficient 0.65 x 10-5 w5 / 2 °C), due to thermal stress during operation. There was a problem in that a crank occurred at the boundary between the terminal 5 of the integrated circuit Takako and the terminal 6 of the printed circuit board.

fd+ OBJECTS OF THE INVENTION An object of the present invention is to improve the layer structure of a multilayer printed circuit board and to provide a printed circuit board on which integrated circuit elements can be directly mounted.

(el) Structure of the Invention This object is achieved by providing a layer of a resin having heat resistance and a small elastic modulus as a surface layer in a multilayer printed circuit board.

(fl Stress σ that generates a crank at the boundary between the terminal 5 of the integrated circuit element and the terminal 6 of the printed circuit board due to thermal stress during operation of the embodiment of the invention
is obtained by the following formula, where As is the coefficient of thermal expansion of the ceramic, Es is the coefficient of elasticity, Ts is the plate thickness, Ap is the coefficient of thermal expansion of the printed circuit board, E is the coefficient of elasticity, is Tp is the plate thickness, and T is the temperature difference. I can do it.

σ=(8p-As) T/ (1/Es +Ts/
Tp -1/Ep) Ts=Tp, A= (Ap
As) T, then σ=A/ (1/Es+1/E
p) In the above equation, if Es is extremely larger than Ep, σ can be considered to be equal to EpA.

In other words, even if the coefficient of thermal expansion of the surface layer material of the printed circuit board is the same, if the elastic coefficient is small, the stress σ at the boundary between the terminal 5 of the integrated circuit element and the terminal 6 of the printed circuit board will be small, and the occurrence of cranks will be reduced. .

The present invention will be explained in detail below with reference to the accompanying drawings.

FIG. 3 shows one embodiment of the present invention, and the same objects as in FIG. 1 are denoted by the same symbols. The intermediate layer of a multilayer printed circuit board is a printed circuit board a or b made of an epoxy resin or polyimide resin plate 1 covered with copper foil 2 on one or both sides, as in the past. A printed circuit board d in which a copper foil 2 is pasted on one or both sides of a plate 7 made of a resin having a small elastic modulus, such as polybutadiene resin, etc.
is used.

The coefficient of thermal expansion of polybutadiene resin is the same as that of epoxy resin or polyimide resin, but the elastic modulus is 1/10 of that of epoxy resin or polyimide resin (the elastic modulus of polybutadiene resin is 20X103kg/cl+,
The elastic modulus of epoxy base material or polyimide base material is 20
x 104kg/cal), which is 1/1 compared to ceramic's elastic modulus of 3 (lxlO" kg/cn!)
It is 50.

Therefore, from the above formula, it is thought that the stress generated at the boundary between the terminal 5 of the integrated circuit element and the terminal 6 of the printed circuit board is approximately proportional to the elastic modulus of the surface layer of the printed circuit board, and is 1/10 smaller than that of a conventional printed circuit board. can be reduced.

Effects of the Invention As described above, according to the present invention, the stress that causes cranking at the boundary between the terminal of an integrated circuit element and the terminal of a printed circuit board due to thermal stress during operation can be reduced to approximately 1/10, It is possible to provide a printed circuit board on which integrated circuit elements can be directly mounted.

[Brief explanation of the drawing]

FIG. 1 shows the layer structure of a conventional multilayer printed circuit board, FIG. 2 shows an integrated circuit element mounted directly on the printed circuit board, and FIG. 3 shows an embodiment of the present invention. In the figure, 1 is an epoxy resin or polyimide resin plate, 2 is a copper foil, 3 is a multilayer printed circuit board, 4 is a ceramic board, 5.6 is a terminal, 7 is a resin plate that is heat resistant and has a small elastic modulus, a is a printed circuit board with copper foil 2 stretched on one side of board 1, b is a printed circuit board with copper foil 2 stretched on both sides of board 1, C is an adhesive, and d is a printed circuit board with copper foil 2 stretched on one or both sides of board 7. The printed circuit board is shown.

Claims (1)

[Claims] A multilayer printed circuit board, characterized in that a layer of a resin having heat resistance and a small elastic modulus is provided as a surface layer.