JPH0418748A - Lead frame for ceramic package - Google Patents

Abstract

PURPOSE:To prevent an incomplete seal which is caused by gas and to contrive the improvement of the productivity and yield of a semiconductor device by a method wherein improvements are made on a lead frame itself. CONSTITUTION:A semiconductor chip is mounted on a cavity 3 formed in a ceramic substrate 1 and after inner leads 2a and 2b of a lead frame 2 are respectively connected with each electrode pad of the chip, a cap is made to cover and the chip is hermetically sealed by melting glass to constitute a semiconductor device. When heat is applied and the chip is hermetically sealed, gas is generated from a mounting paste, but this gas inclines to flow out uniformly by making equal gaps P1, P2 and P3 which are formed between the mutually adjacent inner leads 2a and 2a, 2b and 2b and 2a and 2b of the frame 2. Thereby, the force of the gas to incline to flow out is equally dispersed, an increase in a gas pressure which is applied to each one part of the gaps formed between the inner leads is prevented by the frame 2 and an incomplete seal between the substrate 1 and the cap is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a lead frame for a ceramic package used as an external terminal when a semiconductor chip is hermetically sealed in a ceramic package.

(Prior Art) In a semiconductor device, each electrode pad provided on a semiconductor chip generally has a different vertical and horizontal arrangement depending on the design method, etc., and the pitch between adjacent electrodes in the arrangement along the length direction is different. There were variations in the pitch between adjacent electrodes in the array along the width direction. After designing the semiconductor chip, a ceramic package is designed with a lead frame as an external terminal corresponding to the placement position of each electrode pad on the semiconductor chip, and the semiconductor chip is hermetically sealed in this package. This was commonly done.

For this reason, lead frames used as the external terminals have generally been constructed as shown in FIGS. 3 and 4.

That is, for example, a glass-sealed ceramic package is constructed by printing and melting low-melting glass on the surface of a ceramic substrate 1 and fixing a lead frame 2' to the surface, as described below. In order to correspond to the positions of the electrode pads of the semiconductor chip mounted on this package, the interval P1' of the gap formed between each inner lead 2'a, 28' along the length direction of this lead frame 2' is Each inner lead 2 along the width direction
Although the distance P 2 ' formed between the inner leads 2' and 2b' was made to be uniform to some extent, the distance between the inner leads 2' and the inner leads 2'a, especially at the four corners.

The distance P3' formed between 2' and 2'b was considerably wide.

Then, a semiconductor chip (not shown) is fixed to a cavity 3 formed approximately at the center of this ceramic substrate 1 via mounting paste, and each inner lead 2r a, 2t b of the lead frame 2' and each of the semiconductor chip After electrically connecting the electrode pads with bonding wires such as Ag wires, cover with a cap (not shown) and
A semiconductor device was constructed in which a semiconductor chip was hermetically sealed in a ceramic package by melting the underlying glass in a furnace at approximately 0°C.

Here, when the semiconductor chip housed in the package is hermetically sealed by applying heat to melt the upper and lower glass as described above, gas is generated from the mounting paste that fixes the semiconductor chip. As a countermeasure against the generated gas, it has generally been the case that the mounting paste itself is used as a countermeasure.

(Problems to be Solved by the Invention) However, as the semiconductor chip size increases and the number of pins increases, the package size tends to increase and the amount of mounting paste for fixing the semiconductor chip also tends to increase. Therefore, the pressure of the gas generated from this mounting paste also gradually increases. Then, when the pressure of the gas inside the package that is generated when the package is hermetically sealed by applying heat increases, this gas spreads to the inner leads 2'a2'b in the widest areas, especially the four corners.
The glass tends to flow out from the gap P3' between them, and the glass located there sinks, causing sealing defects, causing negative effects such as preventing uniform sealing, and causing problems such as a decrease in productivity and yield. I've come to do it.

That is, as conventional ceramic packages have become larger, it has become increasingly difficult to use the mounting paste itself to deal with sealing failures caused by gases generated by the mounting paste.

In view of the above, the present invention improves the lead frame itself to prevent seal failure caused by gas.
The purpose is to provide a product that improves productivity and yield.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, a lead frame for a ceramic package according to the present invention is a ceramic package that is used as an external terminal when a semiconductor chip is hermetically sealed in a ceramic package. In a lead frame for a bankage, the intervals between the gaps formed between adjacent inner leads of the lead frame are approximately equal over the entire circumference.

(Function) According to the present invention having the above configuration, the gas generated from the mounting paste when the semiconductor chip is mounted and covered with a cap and then heat-hermetically sealed is removed from each inner lead of the lead frame adjacent to each other. The lead frame itself prevents the gas from flowing out uniformly from the equally spaced gaps formed between the inner leads, and thereby increasing the gas pressure in some of the gaps formed between the inner leads. This makes it possible to prevent seal failure between the ceramic substrate and the cap.

(Example) An example of the present invention will be described below with reference to FIGS. 1 and 2.

This figure shows a Cerve type package (Cervive type package) which is a glass-sealed ceramic package similar to the conventional example above.
The ceramic package is constructed by printing low-melting glass on the surface of a ceramic substrate 1, melting it, and fixing a lead frame 2 to the surface.

This lead frame 2 has a gap interval P1 formed between each inner lead 2a, 2a along its length direction, and a gap P1 formed between each inner lead 2b, 2b along its width direction.
The interval P2 formed between them is equal to 2 (P1=P2
), and each inner lead 2a located at the four corners,
The interval P3 formed between the intervals P1 and 2b is also the same as each interval P1. P2
(Pl-P2=P3').

That is, one of the inner leads 2a arranged along the length direction and located at the ends or the inner leads 2b arranged along the width direction and located at the ends (
In the figure, the width of the inner leads 2b) arranged along the width direction and located at the ends is widened, and the inner leads 2b) are extended in other directions so that there are no gaps in the corners. There is.

That is, the gaps between the inner leads at the relatively wide corners, which generally occur in the prior art, are closed by the inner leads 2a or 2b of the lid frame 2, so that such gaps do not occur.

Then, a semiconductor chip (not shown) is fixed to a cavity 3 formed approximately in the center of this ceramic substrate 1 via mounting paste, and each inner lead 2a, 2b of the lead frame 2 and each electrode pad of the semiconductor chip are connected to each other. Ag
After making electrical connections using bonding wires, etc., a cap (not shown) is placed on the cap, and the glass on the top and bottom is melted in a furnace at about 450°C to seal hermetically to form a semiconductor device. .

Gas is generated from the mounting paste when the semiconductor chip is mounted, covered with a cap, and hermetically sealed by applying heat.

2a, 2b, 2b and each equal gap P1 formed between 2a, 2b. P2. It will try to flow out uniformly from P3 (Pl-p2-P3).

As a result, the force of the gas trying to flow out is evenly distributed, and the inner leads 2a, 2a, 2b2b and 2a
The lead frame 2 prevents the gas pressure from increasing in a part of the gap formed between the ceramic substrate 1 and the cap, thereby preventing seal failure between the ceramic substrate 1 and the cap.

Note that the above example shows an example of use in a glass-sealed ceramic DIP type package, but it cannot be used for any ceramic package where sealing failure due to gas is a concern, including glass-sealed ceramic packages in general. Of course.

[Effects of the Invention] Since the present invention has the above-mentioned configuration, the gas generated from the mounting paste tends to flow out when the ceramic package is heated and the semiconductor chip housed inside is hermetically sealed. The bias in force is prevented by the lead frame, thereby preventing seal failure between the ceramic substrate and the cap, thereby improving productivity and yield.

Moreover, there is an advantage that a semiconductor device can be constructed using the same process as a conventional ceramic package.

[Brief explanation of drawings]

1 and 2 show an embodiment of the present invention. FIG. 1 is a plan view of a lead frame placed on a ceramic substrate, FIG. 2 is an enlarged view of the FIG. 3 is a diagram corresponding to FIG. 1 showing a conventional example, and FIG. 4 is an enlarged view of the section ■ in FIG. 1...Ceramic substrate, 2...Lead frame, 2
a, 2b...inner lead, 3...cavity.

Claims (1)

[Claims] In a lead frame for a ceramic package used as an external terminal when a semiconductor chip is hermetically sealed inside a ceramic package, the interval between each gap formed between each adjacent inner lead of the lead frame is measured around the entire circumference. A lead frame for a ceramic package, characterized in that the lead frame is approximately equal across the length.