MPXM2102AS datasheet(29/670 Pages) MOTOROLA

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Motorola Sensor Device Data

www.motorola.com/semiconductors

Interfacial Permeability

Lead leakage is a specific example of interfacial

permeability. It is pressure leakage through the polymer

housing material/metallic leadframe material interface from

the inside of the pressure sensor package to the outside of the

pressure sensor package or vice versa [22]. In addition, other

material interfaces can result in leakage. We describe another

specific example of this in the next section. Lead leakage is

like polymer swelling in that it may allow another failure

mechanism, like corrosion, to occur more readily. It also

causes a systematic pressure measurement error. Figure 8

shows the result of lead leakage measurements as a function

of temperature cycling. The polymer housing material (and its

CTE as a function of temperature), the leadframe material

(and its CTE), surface preparation and contamination, the

polymer matrix composition, and polymer processing all

contribute to this effect. It is accelerated by media,

temperature cycling, and applied pressure.

Figure 8. Pressure leakage measurements through the metallic leadframe/polymeric housing material interface on a

pressure sensor as a function of temperature cycles between –40 and 125

°C.

0.0

0.5

1.0

1.5

2.0

TEMPERATURE CYCLES

EPOXY

PPS GRADE 1

200

400

600

800

1000

PPS GRADE 2

PBT

LCP

Adhesive Strength

Packaging of the sensor relies on adhesive material to

maintain a seal but not impart stress on the piezoresistive

element. Polymeric materials are the primary adhesive

materials which can range from low modulus material such as

silicone to epoxy with a high modulus. An example of a typical

joint is shown in Figure 9. The joint has three possible failure

locations

with

the

preferred

break

being

cohesive.

Contributors to a break include whether the joint is in tension

or compression, residual stresses, the adhesive material,

surface preparation, and contamination. An adhesive failure

is accelerated by media contact, cyclic or static temperature,

and cyclic or static stress (e.g. pressure).

Figure 9. Failure locations for an adhesive bond of

dissimilar materials.

DIE TO EPOXY

ADHESIVE

STRENGTH

COHESIVE

STRENGTH

DIE TO MAT’L

ADHESIVE

STRENGTH

Strength Components

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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