Method for manufacturing a pressure sensor

Details Method for manufacturing a pressure sensor Method for manufacturing a pressure sensor

2000-06-26

2001-10-09

Niebling, John F. (Department: 2812)

Semiconductor device manufacturing: process

Packaging or treatment of packaged semiconductor

Encapsulating

C438S126000, C438S112000, C438S051000, C264S328140, C264S478000, C264S327000

Reexamination Certificate

active

06300169

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a pressure sensor.
BACKGROUND OF THE INVENTION
A method for manufacturing a pressure sensor is described, by way of example, from the publication “Advanced Microsystems for Automotive Applications '99, D. E. Ricken, W. Gessner, p. 126.” In that method, a semiconductor pressure sensing element, which has, applied on a base, a semiconductor chip having a pressure membrane, is applied onto a lead grid, a so-called lead frame. A planar segment of the lead grid, a so-called die pad, functions in this context as assembly segment of the semiconductor pressure sensing element. Subsequently, the semiconductor chip is connected to contact segments of the lead grid via bonding wires. In a transfer molding process referred to as “transfer molding,” which is also referred to as transfer forming, the semiconductor pressure sensing element is then embedded in a housing made of injection molding compound (mold compound). The pressure feed of the sensor, in this context, can issue from the upper side of the semiconductor pressure sensing element or through a pressure channel connected to the lower side of the semiconductor chip and provided in the base and the assembly segment. In carrying out the method, care should be taken in the injection molding of the semiconductor pressure sensing element that a pressure feed in the housing is kept free of the injection molding compound. In the method, this occurs through the use of a tool part, which is pressed, in the injection molding die, either against the upper side of the semiconductor pressure sensing element or against the assembly segment, depending on whether the pressure feed is to proceed from the side of the semiconductor pressure sensing element facing away from the lead grid or from the side facing the lead grid. After the injection molding process, the tool part is removed, as a result of which a recess remains in the injection molding compound, which functions as the pressure feed.
In the method discussed above, it is disadvantageous that the stamp must be pressed against the semiconductor sensor or the assembly segment of the lead grid. In response to the pressing of the stamp on the semiconductor pressure sensing element, the membrane of the semiconductor chip can be damaged. In response to the pressing of the stamp against the assembly segment of the lead grid furnished with a pressure channel, the assembly segment can move relative to the contact segments laid down in the injection molding die, so that between the assembly segment and the stamp a gap arises into which injection molding compound can penetrate.
SUMMARY OF THE INVENTION
As a result of the method according to the present invention, the known disadvantages are avoided. In the method according to the present invention, the stamp does not reach or touch the semiconductor pressure sensing element or the assembly segment, but rather, in the injection molding die, is separated by a gap from the semiconductor pressure sensing element or the assembly segment. By changing the temperature of the stamp relative to the temperature of the liquefied injection molding compound, the flow properties of the injection molding compound are reduced and, in the area of the stamp, as a result, at least a complete penetration is avoided of the injection molding compound into the gap between the stamp and the semiconductor pressure sensing element or into the gap between the stamp and the assembly segment. In this context, use is made of the temperature dependence of the flow properties of the injection molding compound. In the injection molding of the semiconductor pressure sensing element, injection molding compounds are used whose flow property is markedly dependent on the temperature. By altering the temperature of the stamp, the fluidity of the injection molding compound is reduced in the area of the stamp, so that the injection molding compound does not penetrate into the gap, or does so only slightly. As a result, a pressure feed in the housing can advantageously be kept free of injection molding compound without the membrane of the semiconductor pressure sensing element or the assembly segment, in the injection molding die, being touched by the stamp.
In a first exemplary embodiment, the viscosity of the injection molding compound in the area of the stamp is increased by cooling the stamp such that the injection molding compound does not penetrate into the gap, or at least does not do so completely.
In a second exemplary embodiment of the method, by heating the stamp, the injection molding compound is wetted and cured more rapidly in the area of the stamp, so that the injection molding compound can only slightly penetrate into the gap, or not all.


REFERENCES:
patent: 5368805 (1994-11-01), Motai
patent: 5672549 (1997-09-01), Minami et al.
patent: 6074195 (2000-06-01), Belous
patent: 6153141 (2000-11-01), Kim et al.
Ricken et al.,Advanced Microsystems for Automotive Applications, '99, p. 126.

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