Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Of specified material other than unalloyed aluminum
Reexamination Certificate
2003-05-22
2004-11-30
Potter, Roy (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Of specified material other than unalloyed aluminum
C257S737000, C257S778000
Reexamination Certificate
active
06825560
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to mounting electronic surface mount devices to a mounting structure, and more specifically relates to a solder or conductive epoxy including filler to be used to mount surface mount devices to a mounting structure.
BACKGROUND OF THE INVENTION
Typically, the process of mounting a surface mount device to a mounting structure includes placing a conductive attach material such as solder or conductive epoxy on electronic contact pads of the structure, aligning electronic contact pads of the surface mount device with the contact pads of the structure, and placing the contact pads of the surface mount device onto the attach material. Due to the placement of the surface mount device and the force of gravity, the distance between the surface mount device and the structure is difficult to control. Often, the contact pads of the surface mount device come to rest on the contact pads of the structure, which may force the attach material to disperse and possibly short the contact pads of the surface mount device. Further, any subsequent heating of the surface mount device may allow reflow of the attach material, which may also short the contact pads of the surface mount device. In addition, the unpredictable distance between the surface mount device and the mounting structure is undesirable in some radio frequency applications, as the distance may affect circuit performance.
FIG. 1
illustrates a surface mount device
10
mounted to a mounting structure
12
as commonly known in the art. Electrical contact pads
14
and
16
of the surface mount device
10
and the mounting structure
12
, respectively, are connected by attach material
18
. By electrically attaching the contact pads
14
of the surface mount device
10
to the contact pads
16
of the mounting structure
12
, the surface mount device
10
is effectively mounted to the mounting structure
12
. For exemplary purposes, the attach material
18
is solder. The solder
18
is heated such that it is in a molten state when mounting the surface mount device
10
to the mounting structure
12
. The contact pads
14
of the surface mount device
10
are then aligned with the contact pads
16
of the mounting structure
12
, and the surface mount device
10
is placed on the solder
18
, thereby mounting the surface mount device
10
to the mounting structure
12
.
Due to the molten state of the solder
18
and the placing of the surface mount device
10
, a distance d between the surface mount device
10
and the mounting structure
12
is very difficult to control. In some cases, the distance d becomes extremely small and may approach zero. Therefore, the solder
18
may be compressed such that the contact pads
14
of the surface mount device
10
are shorted.
Once the surface mount device
10
is mounted to the mounting structure
12
, the mounting structure
12
may be mounted to a second mounting structure
20
. Contact pads
22
and
24
of the mounting structure
12
and the second mounting structure
20
, respectively, are aligned and electrically connected by attach material
26
. In order to mount the mounting structure
12
to the second mounting structure
20
, the attach material
26
is heated. In the case that the attach material
26
is solder, the attach material
26
is heated into its molten state during attachment. If the attach material
26
is conductive epoxy, the attach material
26
is heated in order to cure the attach material
26
. In either case, the heating of the attach material
26
may reheat the solder
18
connecting the surface mount device
10
to the mounting structure
12
. When reheated, the solder
18
may reflow and short the contact pads
14
of the surface mount device or other conductive areas
Similarly to the distance d, a second distance (not shown) between the mounting structure
12
and the second mounting structure
20
is difficult to control. Therefore, the placement of the mounting structure
12
onto the second mounting structure
20
or the force of gravity may cause the attach material
26
to short the contact pads of the mounting structure
12
.
The above discussion focuses on using solder as the attach material
18
; however, problems similar to those associated with solder exist for other attach materials such as conductive epoxy. Thus, there remains a need for a cost-effective method for controlling the distance d between a surface mount device
10
and a mounting structure
12
and/or between two mounting structures
12
and
20
.
SUMMARY OF THE INVENTION
The present invention relates to electrically attaching a surface mount device to a mounting structure via their respective contact pads using an attach material, such as solder or conductive epoxy, which includes a filler material. In general, the filler material is relatively solid and granular shaped, wherein the diameter of the filler material controls a mounting distance between the surface mount device and the mounting structure. The filler allows the desired distance to be maintained during initial placement of the device and any subsequent reheating. The process of mounting the surface mount device to the mounting structure is achieved by placing the attach material including the filler material on the contact pads of the surface mount device and/or the contact pads of the mounting structure. The contact pads of the surface mount device are aligned with the contact pads of the mounting structure, and the surface mount device is placed onto the mounting structure. As the surface mount device settles into the attach material, the movement of the surface mount device towards the mounting structure is limited by the filler material. Once settled, the distance between the surface mount device and the mounting structure is defined by the diameter of the filler material.
Those skilled in the art will appreciate the scope of the present invention and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures.
REFERENCES:
patent: 6365973 (2002-04-01), Koning
patent: 6518677 (2003-02-01), Capote et al.
Bullis Joseph Byron
Walker Jeffrey Scott
Potter Roy
RF Micro Devices, Inc.
Withrow & Terranova , PLLC
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