Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1998-01-22
2003-10-07
Arbes, Carl J. (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S740000, C029S742000, C029S743000, C029S840000, C174S258000, C174S260000, C361S728000, C361S820000, C156S306600, C156S247000
Reexamination Certificate
active
06629363
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to electronic device packaging. More particularly, this invention includes a process and apparatus for securing a temporary lid to a chip substrate to aid in movement of the chip substrate during automated card assembly operations.
BACKGROUND OF THE INVENTION
The increasing use of ceramic, multiple-chip modules incorporating flip-chip devices has caused correspondingly larger demands on card assembly machines which perform high-speed “pick-and-place” operations. The ever-increasing range of possible chip layouts and encapsulation schemes exacerbates those demands. Therefore, the card assembly machines have had to become, and continue to become, better suited to perform pick-and-place operations on chip modules during card assembly.
Typically, in the case of common, plastic, overmolded, dual-in-line packages (DIPs), automated picking of the components is performed by a vacuum probe. The vacuum probe attaches to the card package by contacting the flat, plastic, outer surface of the chip. The difference in pressure between the ambient atmosphere and the inside of the vacuum probe (with the chip surface sealing the probe opening) keeps the package attached to the probe until the vacuum is released, which releases the package from the tip of the vacuum probe.
FIG. 1
illustrates this process according to the prior art, where vacuum probe
110
is shown attached to the module
100
through contact with chip
120
. The module
100
is typically referred to as a capless chip module. The module
100
of
FIG. 1
is shown as already placed and seated on a printed circuit board
130
.
FIG. 1
also shows additional components of a typical capless chip module
100
seated on top of a printed circuit board
130
, according to the prior art. Printed circuit board
130
supports a plurality of solder balls
140
which in turn support a substrate
150
(often, but not necessarily, ceramic). If the substrate is ceramic, the substrate
150
and its solder balls form what is known as a ceramic ball grid array (CBGA). Alternatively, a ceramic column grid array (CCGA) (not shown) technology could be used. Typically, the chip
120
is secured to the substrate
150
via a plurality of controlled collapse chip connection (C4) balls
145
.
The substrate
150
could also have one or more electronic devices
160
attached to it via the C4 balls
145
. Examples of such electronic devices include: decoupling capacitors, resistors, capacitors, and inverters. In addition, these devices could be attached to the substrate not by C4 balls
145
, but rather by surface-mountable solder (not shown). For reliability reasons, the C4 balls are encapsulated with a polymeric underfill material
170
. Where multiple chips and electronic devices are combined oh one substrate, as in
FIG. 2
, the package is typically referred to as a multiple chip module (MCM).
In a typical card assembly manufacturing process, a pick-and-place tool picks up each module
100
that is to be joined to the printed circuit board and places it in the proper location. The board
130
and these placed modules
100
are then heated in a card assembly heating apparatus and the solder balls
140
are “reflowed” causing the connection of module
100
and printed circuit board
130
to occur.
As MCMs become larger and more specialized, automated pick-up and placement of cap-less modules become more difficult because the chip center lines may be located on an asymmetric grid with respect to the center line of the module. In other words, with a multitude of chips and components on the substrates (as is the trend), there may not be a clean, flat, and smooth surface available in the middle of the module to which the vacuum probe can attach. Non-flat surfaces having encapsulants, glob top, or other polymeric materials also create problems for pick-up tools. Unless the card assembly picking tooling is automated and flexible enough to locate a chip surface off the packaging center (even in a high-speed mode), tool efficiency will suffer greatly, because many chips will simply not be picked up without changes being made in the tooling each time a module type is run. Moreover, many automated pick-and-place tools cannot move off module centers and such tools cannot practically be modified (due, in part, to cost constraints). The vacuum probe method is most economical and efficient for packages having a relatively flat top surface. It is often not well suited, however, to making dynamic, offset motions needed to accommodate off-center device locations, nor is it effective in spanning multiple chips, unless a custom pickup probe is fitted to each package type.
FIG. 3
illustrates another process for moving chip modules
100
during production according to the prior art, where the center of the lid is used for pick and place operations. The module shown in
FIG. 3
is typically referred to as a capped module, because a module cap
210
is used. Here, vacuum probe
110
is attached not to a chip, but rather to module cap
210
. Module cap
210
is attached to substrate
150
of module
100
via a cap seal
220
(adhesive for non-hermetic modules and solder or glass for hermetic modules). Module cap
210
is attached to chips
120
via a semi-liquid or paste-type, thermally conductive material
230
. It is important that cap
210
be attached to each chip
120
through a thermally conductive material because the chips would otherwise overheat during operation. Module cap
210
is typically metal and presents a clean, smooth, flat surface to vacuum probe
110
.
In the package assembly shown in
FIG. 3
, because the cap
210
is attached to the substrate
150
via a cap seal
220
,.the attachment is substantially permanent. If the cap
210
is removed from the substrate
150
at some later step for rework in the manufacturing process, the substrate may be damaged, or seal material may be left behind. Such a condition increases the risk of damage when additional components are subsequently reworked to the substrate
150
. The trend is away from module caps
210
and toward non-hermetic packaging methods.
In the device as illustrated in
FIG. 3
, the chips
120
are attached to the module cap
210
via thermally conductive material
230
which transfers heat from the chips
120
to the module cap
210
where it can be further dissipated. The necessity of a thermally conductive material
230
associated with capped modules adds to the cost of reworking and adds a higher rate of unreliability to the package.
The deficiencies of the conventional manufacturing techniques show that a need still exists for a process and apparatus which will accurately and reliably attach a temporary, removable lid to a chip carrier to allow vacuum pick-up by high-speed, automated assembly tools. Therefore, one object of the present invention is to provide an apparatus and process for attaching a temporary, removable lid to a chip carrier containing one or more microelectronic devices using a mechanical clipping lid which attaches to the substrate via friction that allows efficient vacuum pick-up by high-speed, automated assembly tools.
Another object of the present invention is to provide an easily removable lid attachment which may be removed after the need for vacuum probe attachment is no longer necessary in the manufacturing process. This object would include a removable lid which does not, upon removal, result in mechanical or structural damage to the devices that would impede subsequent heatsink attachment schemes which may involve the use of adhesive compounds.
Still another object of the present invention is to provide a process and apparatus that will absorb thermally induced strain without damage to the chip carrier or associated devices. Still yet another object of the present invention is to provide an apparatus that will allow pressure to be applied to the module during testing and burn-in without damage to the module.
Yet another object of the present invention is to provide a process and apparatus for ensuring mec
RatnerPrestia
Townsend, Esq. Tiffany L.
Trinh Minh
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