JPH0793477B2 - Printed wiring board - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a printed wiring board used as a package for mounting a semiconductor.

[Prior art]

In a semiconductor mounting package used as PGA, PLDCC, PLCC, etc., a package formed of a printed wiring board is the mainstream. That is, a metal foil-clad laminate obtained by laminating a metal foil such as a copper-clad glass-based epoxy resin laminate on a laminate that is the substrate 1 is used to remove unnecessary portions as a circuit by etching the metal foil. As shown in FIG. 3, a printed wiring board A formed by providing a large number of circuits 2, 2, ... On the surface of the substrate 1 is used as a package for mounting a semiconductor. In FIG. 3, 7 is a cavity pad for mounting a semiconductor such as an IC, 8 is a lead wire for plating, and these are formed by leaving a part of the metal foil. Further, in FIG. 3, the line indicated by the symbol a is a line for the final separation, and the inside of the line a is the product (package). In the printed wiring board A as described above, the substrate 1
Each of the circuits 2, 2 ... provided on the substrate is formed in a thin line shape having only a necessary width as a circuit, and the area other than the circuits 2, 2 ... The ratio of is increasing.

[Problems to be Solved by the Invention]

However, the fact that the ratio of the area occupied by the portion other than the circuits 2, 2 ...
That is, the area of the exposed portion of the surface of the substrate 1 that is not covered by the circuits 2, 2 ... Is increased. Therefore, when the metal foil is stretched, the metal foil can block the moisture, so that the substrate 1 hardly absorbs moisture. However, the metal foil is thus etched to form the circuits 2, 2 ... When the plate A is processed, there is a problem that the substrate 1 absorbs moisture from the exposed surface which is not covered with the circuits 2 and so that the insulating performance of the substrate 1 deteriorates. In particular, as shown in FIG. 3, circuits 2,2
, Are arranged radially from the periphery of the cavity pad 7 in the substantially central portion of the substrate 1 to the peripheral portion of the substrate 1, each circuit 2
However, the distance between the end portions on the peripheral edge side becomes large, and the exposed area of the peripheral edge portion of the substrate 1 becomes extremely large, so that the above-mentioned problems occur greatly. In addition, semiconductor packages are required to have high reliability in order to mount industrial large-scale high-performance chips, and moisture absorption, which is a weak point of printed wiring boards formed from resin-based boards, and insulation deterioration due to this moisture absorption. Need to be reduced as much as possible. In particular, as shown in FIG. 3, when the circuits 2, 2 ... Are arranged radially from the periphery of the cavity pad 7 in the substantially central portion of the substrate 1 to the peripheral portion of the substrate 1, each circuit 2 has its peripheral portion. The space between the end portions on the side becomes large, and the exposed area of the peripheral portion of the substrate 1 becomes extremely large, which causes the above-mentioned problems to occur. The present invention has been made in view of the above points, and an object of the present invention is to provide a printed wiring board for a semiconductor package that can reduce moisture absorption of a substrate and does not have a possibility of deteriorating the insulation performance of the substrate. It is what

[Means for Solving the Problems]

According to the present invention, in a printed wiring board formed by providing a large number of circuits 2, 2 ... With a metal conductor on the surface of a substrate 1 mainly composed of a resin, a pad 7 for a cavity at a substantially central portion of the substrate 1 is formed.
The circuit 2 radially arranged from the entire periphery of the substrate 1 to the entire peripheral edge of the substrate 1 is provided on almost the entire surface of the substrate 1 by providing only the gaps 3 necessary for separating the circuits between the adjacent circuits 2. It is characterized by being formed.

[Work]

In the present invention, only the gaps 3 necessary for separating the circuits are provided between the adjacent circuits 2 so that the circuits 2, 2 ... Are formed on almost the entire surface of the substrate 1. It is possible to reduce the area of the exposed portion of the surface of No. 1 which is not covered by the circuits 2, 2, ..., And it is possible to reduce moisture absorption of the substrate 1.

【Example】

Hereinafter, the present invention will be described in detail with reference to examples. The printed wiring board A can be formed by processing a substrate 1 such as a laminated plate mainly made of resin and having a surface covered with a metal foil. For example, by using a metal foil-clad laminate obtained by laminating a metal foil such as a copper-clad glass-based epoxy resin laminate plate on the laminate plate that is the substrate 1, the metal foil-clad laminate plate is subjected to etching treatment or the like to form a circuit 2,2.
The printed wiring board A can be formed by forming the circuits 2, 2 ... On the substrate 1 by removing the unnecessary portions of the circuit 2 while leaving the portions that become ... In the present invention, the gap 3 between the adjacent circuits 2 insulates the circuits 2 as shown in FIG. 1 (in FIG. 1, the portions of the metal foil left unetched are shown by hatching). It is formed so as to have a narrow width necessary for That is, the circuits 2, 2 ... Are formed as wide as possible, and the gap 3 between the circuits 2 formed by etching away the metal foil is made as narrow as possible. Therefore, as is clear from FIG. 1, the area of the exposed portion of the surface of the substrate 1 which is not covered with the circuits 2, 2 ... Is small. Thus, the printed wiring board A formed by providing a large number of circuits 2, 2, ... On the surface of the substrate 1 is used as a package for mounting electronic elements. In FIG. 1, 7 is a cavity pad for mounting a semiconductor such as an IC, 8 is a lead wire for plating, and these are formed by leaving a part of the metal foil. , 2, ... Are formed radially so that one end is located near the cavity pad 7 and the other end is continuous with the plating lead wire 8. Reference numeral 9 denotes a land provided in each circuit 2. By providing a through hole in this land 9, a connecting pin can be attached. In addition, the line indicated by the symbol a in FIG. 1 is a line for final separation, and the inside of the line a is the product (package). The present invention can be applied to any type such as a double-sided printed wiring board or a multilayer printed wiring board. In the printed wiring board A formed as described above, it is possible to reduce the area of the surface of the substrate 1 which is exposed without being covered with the circuits 2, 2, ... Therefore, the substrate 1 can be prevented from absorbing moisture from the exposed surface. By the way, the one shown in FIG. 1 (example) and the one shown in FIG. 3 (conventional example)
The pressure cooker test under the conditions of 121 ° C and 2 atm, and its insulation resistance (consisting of the interlayer resistance when the interlayer thickness is 0.4 mm and the inner layer circuit resistance when the circuit distance is 0.2 mm) and the pressure cooker When the relationship with the processing time is measured, the results shown in the graph of FIG. 2 are obtained. As can be seen in the graph of FIG.
It is confirmed that the embodiment shown in the figure has a slower deterioration of the insulation performance than the conventional example shown in FIG. 3, and the speed of moisture absorption can be slowed.

【The invention's effect】

As described above, in the present invention, the circuit radially arranged from the entire periphery of the cavity pad at the substantially central portion of the substrate to the entire peripheral portion of the substrate is used to separate the circuits between the adjacent circuits. Since only the necessary gaps are provided and formed on almost the entire surface of the substrate, it is possible to reduce the gap between the circuits from the periphery of the cavity pad to the peripheral portion of the substrate. It is possible to reduce the area of the exposed part that is not covered with, and it is possible to reduce the moisture absorption of the substrate by blocking a large area of the substrate with a metal circuit, and the insulation deterioration of the substrate occurs. It can prevent that.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of the present invention, FIG. 2 is a graph showing the relationship between insulation resistance and pressure cooker processing time, and FIG. 3 is a plan view of a conventional example. 1 is a substrate, 2 is a circuit, 3 is a gap between the circuits, and 7 is a cavity pad.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toru Higuchi 1048, Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Works, Ltd. (56) References JP-A 64-59985 (JP, A) JP-A 63-140627 ( JP, A)

Claims (1)

[Claims] 1. In a printed wiring board formed by providing a large number of circuits of a metal conductor on the surface of a substrate mainly made of resin, from the entire periphery of the cavity pad in the substantially central portion of the substrate to the entire peripheral edge of the substrate. Circuits arranged in a radial pattern are provided with only the gaps necessary to separate the circuits between adjacent circuits,
A printed wiring board for a semiconductor package, which is formed on almost the entire surface of a substrate.