Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
1999-09-01
2001-05-29
Lam, Cathy (Department: 1775)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S255000, C174S256000, C174S259000, C428S210000
Reexamination Certificate
active
06239382
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to preventing bowing of a stacked, soldered, adhesively bonded, or otherwise connected assembly, and, more particularly, to a method and device that prevent bowing of the assembly when it is exposed to change in temperature.
BACKGROUND OF THE INVENTION
Optoelectric devices and electronic components having microelectronic, optoelectronic or photonic components or devices (such as, lasers, for example), are often mounted on bases (assemblies) that consist of a plurality of stacked, dissimilar materials. In such devices, a component is typically mounted to a (first) material that is, in turn, secured to a second, dissimilar, material; such dissimilar materials being attached, using solder, an adhesive, or the like. During the attachment (e.g.,) soldering process, the electronic assembly is exposed to an elevated temperature (e.g., high enough to cause the solder to re-flow) and subsequently cooled down to a lower temperature. The different coefficients of thermal expansion (CTE) in dissimilar materials cause the materials to expand (or contract) at different rates in response to changes in temperature. As a result, the base (assembly) can experience appreciable (residual curvature). At the same time, proper operation of a photonic device requires precise optical alignment between and among the devices, lensed fibers, etc. mounted to the first material. For example, a lateral misalignment of only 0.5 &mgr;m between the lightguides (e.g., a laser and a lensed optical fiber) will render the optoelectric device inoperable.
Bowing of the base (assembly) is currently compensated for by aligning the various optical components mounted on the base after the assembly is manufactured. This procedure, referred to as active alignment, is costly and time consuming. Moreover, active alignment only addresses the misalignment before the electronic device is installed or deployed for use; after which deviation in the flatness of the base may not be corrected.
It is thus desirable to provide a method for controlling the bowing of a multi-material assembly that overcomes the above-described shortcomings of the prior art.
SUMMARY OF THE INVENTION
The present invention is directed to a method of controlling (i.e., minimizing) the bowing of an assembly by controlling the location, thickness, and characteristics of the materials of the solder (adhesive) layers used to construct the base.
In a first embodiment, the present invention comprises a method of controlling the bowing of an electronic assembly, where the base (assembly) is comprised of a plurality of stacked, dissimilar materials. The inventive method formulated in application to a soldered bi-material assembly, comprises the steps of providing a first material, having a thickness h
1
, and providing a second material that is different from the first material and having a thickness h
2
. The method further comprises the step of providing a third (“adhesive”) material that is different from the first and second materials, secures the first and second materials together in stacked relation to each other, and is located between the first and the second materials at a position determined by the equation:
T
1
h
1
+T
2
h
2
=0,
where T
1
and T
2
are thermally induced forces due to thermal expansion (contraction) mismatch caused by the dissimilar materials in the assembly.
In a second embodiment, the method of the present invention comprises the steps of providing a first material, having a thickness h
2
, and providing a second material that is different from the first material and having a thickness h
1
. The inventive method also includes the step of providing a third material that is different from the first and second materials and that has a thickness h
3
adequate to prevent bowing of the assembly. The third material acts as an adhesive and secures the first and second materials together in stacked relation to each other and is located between the first and the second materials.
In a third embodiment, the method of the present invention comprises the steps of providing a first material having a thickness h
1
and providing a second material that is different from the first material and having a thickness h
2
. The inventive method further comprises the step of providing a third material that is different from the first and second materials and that has a Young's modulus and/or a coefficient of thermal expansion adequate to prevent bowing of the assembly. The third material acts as an adhesive and secures the first and second materials together in stacked relation to each other and is located between the first and second materials.
The three embodiments may be used separately, or in any combination to control the bowing of the base of an assembly.
The present invention is also directed to an assembly comprising a base having a first component and a second component, each mounted to the base and in operable alignment with each other. The base comprises a plurality of stacked, dissimilar materials, including a first material that has a thickness h
1
, and a second material that is different from the first material and that has a thickness h
2
, and a third material that is different from the first and second materials, that secures the first and second materials together in stacked relation to each other, and that is located between the first and second materials at a position determined by the equation
T
1
h
1
+T
2
h
2
=0,
where T
1
and T
2
are thermally induced forces caused by the thermal expansion (contraction) mismatch caused by the different first and second materials. The location of the third material in the assembly with respect to the first and second materials prevents the bowing of the assembly beyond a predetermined amount so as not to impair operation of the electronic or photonic component or device.
The present invention is further directed to an assembly comprising a base having a first component and a second component, each mounted to the base and in operable alignment with each other. The base comprises a plurality of stacked, dissimilar materials, including a first material that has a thickness h
1
, and a second material that is different from the first material and that has a thickness h
2
, and a third material that is different from the first and second materials and that has a thickness h
3
that is sufficient to prevent bowing of the base. The third material secures the first and second materials together in stacked relation to each other and is located therebetween.
The present invention is also directed to an assembly comprising a base having a first component and a second component, each mounted to the base and in operable alignment with each other. The base comprises a plurality of stacked, dissimilar materials, including a first material that has a thickness h
1
, and a second material that is different from the first material and that has a thickness h
2
, and a third material that is different from the first and second materials and that has a Young's modulus and/or a coefficient of thermal expansion that is sufficient to prevent bowing of the base. The third material secures the first and second materials together in stacked relation to each other and is located therebetween;
Other objects and features of the present invention will become apparent from the following detailed description, considered in conjunction with the accompanying drawing FIGURE. It is to be understood, however, that the drawings, which are not to scale, are designed solely for the purpose of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims.
REFERENCES:
patent: 6028772 (2000-02-01), Suhir
Agere Systems Guardian Corp.
DeCarlo. Esq. James J.
Lam Cathy
Stroock & Stroock & Lavan LLP
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