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Flip Chip mounted gas flow sensor Disclosure Number: IPCOM000240970D
Publication Date: 2015-Mar-16
Document File: 4 page(s) / 313K

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Roland Cerna: AUTHOR [+3]


In this publication, flip chip mounted gas flow sensors in various embodiments are disclosed.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 51% of the total text.

Page 01 of 4

Flip Chip mounted gas flow sensor

R. Cerna, M. Hornung und W. Hunziker; Sensirion AG

In this publication, flip chip mounted gas flow sensors in various embodiments are disclosed.

Commonly, chips for environmental sensing are electrically connected to a substrate, e.g. PCB or leadframe, by a wire bonding process. The wire bonding process is followed by an encapsulation process to insulate and protect the wires. This can be performed e.g. by a glob top or molding process. For these sensors, encapsulation processes are needed, which protect the wires but keep the sensitive area free.

Another method for mounting chips is the flip chip method. In this method, the chip is attached with its front side, i.e. the side where the CMOS is located, to a substrate. Electrical contacts between chip and substrate are made by conductive bumps. Different types of bumps are used on chip and /or substrate side depending on used flip chip technology. For easy mounting on PCB, solder bumps are primarily used. After the soldering process, an underfill is normally applied for better mechanical stability. For sensor chips, the flip chip method is challenging since the sensitive area, which is usually placed on the front side of the chip, needs to be accessible to the environment. However, flip chip assembly is desirable since it offers many advantages, of which costs and assembly efficiency are the most important ones. A flip chip assembly process, which solves the mentioned problems for temperature and humidity sensors, is disclosed in the international patent application WO2011/060558A1.

Here, we focus on flip chip mounting for gas flow sensors. In this case, requirements for access of the environment to the sensitive area are even higher than for temperature and humidity sensors. The gas flow in the environment has to create a proportional secondary flow over the sensitive area of the chip. Therefore, inlet and outlet openings to the environment are needed. Various embodiments of flip chip mounting for gas flow sensors are illustrated in figures 1 and 2. It is inherent to the flip chip mounting process that a gap between chip and substrate arises (for a plane substrate, which is usually the case). The size of the gap is given by the height of the solder balls. Here we take advantage of this gap and use it to create a flow channel. As it is illustrated in figure 2, the solder balls can be situated on one, or both sides of the flow channel. The minimum number of solder balls is given by the necessary number of electrical contacts, however more solder balls may be used, e.g. for stability reasons. By referring to solder balls we do not exclude any other shape or material which could be used for electrical contacts.

In the case where no underfill is used, the assembly can be used for flow measurements without any further process steps as illustr...