Connecting of semiconductor chips to circuit substrates

A method and article made by such method are described for connecting electrodes on one face of an integrated circuit semiconductor device with those on a supporting substrate. The method comprises positioning electrodes formed on one face of the device into engagement with electrodes formed on the substrate. A force is applied to press the electrodes together and during application of the force a first adhesive is applied along only a minor portion of two edges of the device. The first adhesive is stiffened to provide a temporary connection of the device and the substrate. A mass of a second adhesive is applied over a face of said device opposite said one face and onto portions of the substrate adjacent the periphery of the device with substantially no adhesive located between the one face of the device and the substrate at a center area of the one face. The second adhesive is hardened to form an adhesive dome that permanently connects the device to the substrate.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a method of connecting semiconductor chips or 
dice to circuit substrates such as circuit boards. 
2. Description of the Prior Art 
In the prior art it is well known to connect semiconductor chips or dice to 
circuit substrates such as circuit boards, with adhesive. As noted in U.S. 
Pat. No. 5,012,969, methods are known for mounting a semiconductor up on a 
circuit substrate so that the semiconductor is placed face down on the 
circuit substrate in what is called a flip-chip arrangement. In such an 
arrangement, a solder bump may be formed on the electrode of the 
semiconductor die and this bump joined with a wiring electrode on the 
circuit substrate. In such methods, the electrodes of the semiconductor 
device and the electrodes of the circuit substrate are mechanically and 
electrically connected by the solder bumps. A problem in such a connection 
is that a thermal or mechanical stress acts on the semiconductor device or 
circuit substrate and the stress is entirely concentrated on the junctions 
of the solder bumps, possibly resulting in the breakage of some of the 
junctions and the lowering of the device reliability. 
In accordance with one solution to this problem described in U.S. Pat. No. 
4,749,120, an electrode is disposed on a semiconductor die and while 
positioning an electrode of a circuit substrate with the electrode of the 
die, an insulating resin is inserted between the front face of the 
semiconductor die and the circuit substrate and the insulating resin is 
stiffened or hardened while applying pressure to the back face of the 
semiconductor die. By making use of the contracting force of the 
insulating resin at the time of stiffening, the electrode of the 
semiconductor die is pressed against the electrode of the circuit 
substrate thereby obtaining an electrical connection. 
As noted in U.S. Pat. No. 5,012,969, this solution causes a bending stress 
to be formed on the semiconductor die or circuit substrate, and the 
connection between the electrodes is partially impaired and it is 
difficult to obtain a favorable connection. Also, when the pressure is 
high, there is a risk of destroying the semiconductor die. This can be 
particularly a problem with fragile devices other than silicon such as 
GaAs. 
Still further, since the insulating resin is formed on the entire from 
facing surface of the semiconductor die, when the semiconductor die or 
circuit substrate is heated and rises in temperature, the entire 
simulating resin tends to expand. When the force of expansion exceeds the 
contracting force, the electrode at the pressed part and the wiring 
electrode will separate from each other, and this often caused defective 
junctions. To overcome this noted problem of the prior art, the solution 
proposed in U.S. Pat. No. 5,9012,969 is to inject a light and 
heat-stiffening insulating resin about the periphery of the semiconductor 
die, at least in the gap between the die and the circuit substrate while 
applying pressure by means of a pressure tool to urge their respective 
electrodes into intimate contact. Afterwards a light source such as UV is 
placed proximate the periphery to stiffen the adhesive while further 
pressure is applied when irradiating. 
A problem with this approach is that this process is time consuming in that 
light-sensitive adhesives require a light source to be moved about the 
periphery of the device nd the light-sensitive adhesives are relatively 
expansive. 
It is, therefore, an object of the invention to overcome the problems 
associated with the prior art. 
SUMMARY OF THE INVENTION 
In accordance with reinvention, there is provided a method of connecting 
electrodes on one face of an integrated circuit semiconductor device with 
those on a supporting substrate, the method comprising: 
positioning electrodes formed on the one face of the device into engagement 
with electrodes formed on the substrate, applying a first adhesive 
substance along only a minor portion of the peripheral length of edges of 
the device to provide a temporary connection of the device and the 
substrate; and applying a mass of a second adhesive over a face of said 
device opposite said one face and onto portions of the substrate adjacent 
the periphery of the device; and hardening the second adhesive to form an 
adhesive dome that permanently connects the device to the substrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
While the invention will now be described with reference to mounting one 
die upon a substrate, it will be appreciated that plural dies might be 
also mounted upon the same substrate. 
Referring now to FIG. 1, metal electrodes 12 formed on a bottom face 10b of 
a semiconductor die 10, such as a semiconductor integrated circuit device, 
and coated metal electrodes 14 of a circuit board substrate 13 are 
positioned with the electrodes 12 and 14 contacting each other in a 
flip-chip arrangement. SA force is applied to a top face 10a of the die 10 
by means of a pressure tool 5 to force the bumps on electrode 12 of the 
die into engagement with pads of electrodes 14. A light-stiffening 
insulating resin 6 is injected by a suitable dispenser at key points along 
the sides rather than contiguous along all edges of the semiconductor 
device, at least in the gap between the semiconductor device 10 and 
circuit substrate 13 to tack the die to the substrate 13. Only two 
portions of two peripheral edge margins of semiconductor device 1 are 
tacked with the resin. Afterwards, light having a wavelength for 
stiffening the light-stiffening insulating resin 6 is emitted form an 
appropriate source (not shown) near the tacking adhesive. For example, in 
the case of an ultraviolet ray stiffening type resin, ultraviolet rays are 
emitted to stiffen the light-stiffening resin 6. After stiffening, the 
tool 5 is removed. As a result, the electrodes 12 and 14 are electrically 
connected to each other, and the semiconductor device 10 and circuit 
substrate 13 are mutually, but temporarily, adhered by the resin 6. The 
electrodes 12 of the semiconductor device may include gold bumps of, for 
example, 5 to 20 .mu.m as is well known. These bumps may instead be formed 
on the electrode 14 of the circuit substrate. 
The light-stiffening resin after stiffening is, as shown in FIG. 1, present 
at only a minor portion of the peripheral length of each of the edges of 
semiconductor device 10. 
The light-stiffening resin 6 may be either acrylic or epoxy resins 
stiffened by light only, or resins stiffened by both light and heat may be 
used. Alteratively, a tap may be used to provide the temporary tack 
connection. After providing a temporary tack adhesive to all the devices 
or dies to be connected to the substrate, the die may be tested or 
burned-in immediately to facilitate repair. In burn-in testing a souce(s) 
of electrical energy is provided to selected electrodes for suitable 
period(s) of item as is well known. Afterwards, a permanent attachment is 
made by depositing a viscous adhesive resin over the top of each of the 
dies as illustrated in FIG. 2. As the second adhesive resin is caused to 
cure or harden, say by application of heat, light and/or through passage 
of time, a dome 20 is formed over each of the dies. In addition to 
providing a permanent connection of each of the dies to the substrate, the 
second adhesive, which may be an epoxy, may also provide a hermetic seal 
to a die. Alternatively, if the characteristics of the adhesive do into 
provide a hermetic seal, a separate conformal coat may be overcoated upon 
the adhesive dome suing a material that will provide the hermetic seal 
with the absence of adhesive at a center area of the bottom face 10b, 
between the bottom face 10b and the substrate 13. The coat will follow the 
adhesive easily and not have to cover the abrupt corners of the die. 
The adhesive used may be of a known heat-conductive type for removing heat 
buildup from the die. 
In addition of the benefits recited above, additional advantages are 
provided by the method of the invention. For example, the die while 
pressed against the substrate by tool can also e tested for I.sub.cc (or 
forward-biased unctions) when provided with appropriate input/output 
signals before tacking. This can be especially important in testing of 
dies with ground shield such as CCD's or other light-sensitive dies. A 
burn-in testing step at the substrate level may also be made before 
permanently securing the die to the substrate with the viscous adhesive 
that forms the dome. In addition repairability is earlier since virtually 
all the adhesive is visually accessible and not trapped under all areas of 
the die. 
the invention has been described in detail with particular reference to a 
preferred embodiment thereof, but it will be understood that variations 
and modifications can e effected within the spirit and scope of the 
invention as described hereinabove and as defined in the appended claims.