Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Insulative housing or support
Reexamination Certificate
2000-09-01
2004-06-29
Chen, Jack (Department: 2813)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Insulative housing or support
C438S108000, C438S780000, C257S701000, C257S778000, C228S180220
Reexamination Certificate
active
06756253
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to semiconductor manufacture, and more particularly to an improved semiconductor component, and to a method for fabricating the component.
BACKGROUND OF THE INVENTION
Semiconductor components, such as packages, dice and wafers can include external contacts in the form of solder contact balls. The contact balls are in electrical communication with integrated circuits, and other electrical elements, contained on the components. For some components, such as chip scale packages and BGA packages, the contact balls can be arranged in a dense grid array, such as a ball grid array (BGA), or a fine ball grid array (FBGA). The contact balls provide a high input/output capability for a component, and permit the component to be surface mounted to a supporting substrate, such as a printed circuit board (PCB).
FIG. 1A
illustrates a contact ball
10
A bonded to a bonding pad
12
A on a semiconductor component
14
A. In this example, the component
14
A comprises a semiconductor package, such as a chip scale package, or a BGA package. The bonding pad
12
A comprises a BGA pad formed on a backside of the component
14
A out of a solderable metal such as molybdenum or copper.
One conventional method for attaching the contact ball
10
A to the component
14
A uses a solder reflow bonding process. With this method the contact ball
10
A is formed separately out of a non-eutectic solder alloy such as 95%Pb/5%Sn, 60%Pb/40%Sn, 63%Sn/37%Pb, or 62%Pb/36%Sn/2%Ag. Typically, the contact ball
10
A has the shape of a sphere, or a truncated sphere.
Initially, a layer of eutectic solder can be deposited on the bonding pad
12
A using a suitable deposition process such as screen printing to form a eutectic solder fillet
16
A. Typically, the eutectic solder is in the form of a paste. A platen can be used to hold the component
14
A, while the eutectic solder is deposited on the bonding pad
12
A.
Alternately, a flux (not shown) can be applied to the bonding pad
12
A. The flux chemically attacks surface oxides, such that the molten solder can wet the surfaces to be bonded. The flux also performs a tacking function prior to solder reflow. Following application of the flux, the contact ball
10
A can be placed on the bonding pad
12
A in physical contact with the eutectic solder and flux. A fixture can be used to center and maintain the contact ball
10
A on the eutectic solder paste and bonding pad
12
A.
Following placement of the contact ball
10
A on the bonding pad
12
A, the component
14
A can be placed in a furnace at a temperature sufficient to reflow the eutectic solder and form the fillet
16
A. The eutectic solder fillet
16
A metallurgically bonds the contact ball
10
A to the bonding pad
12
A. The component
14
A can then be removed from the furnace and cooled. In addition, the excess flux can be removed from the exposed surfaces of the component
14
A and the contact ball
10
A, using a suitable cleaning agent.
Suitable furnaces for performing the reflow process include convection ovens and infrared ovens. Rather than an oven, the bonding process can be performed using a pulse-thermode, a hot-air thermode, or a laser. A solder ball bumper, for example, uses a laser to form the eutectic solder fillet
16
A, and bond the contact ball
10
A to the bonding pad
12
A. Alternately, the contact ball
10
A can be bonded to the bonding pad
12
A by brazing, by welding, or by application of a conductive adhesive.
Following the bonding process, the component
14
A can be surface mounted to a supporting substrate
24
A, such as a printed circuit board (PCB), to form an electronic assembly
22
A. For attaching the component
12
A to the substrate
24
A, a second eutectic solder fillet
26
A bonds the contact ball
10
A to a contact pad
28
A on the supporting substrate
24
A. A solder reflow process, as previously described, can be used to form the eutectic solder fillet
26
A, and to bond the contact ball
10
A to the contact pad
28
A.
One factor that can adversely affect the reliability of the assembly
22
A during operation in different customer environments is fatigue failure of the contact ball
10
A, particularly at the interface of the contact ball
10
A with the bonding pad
12
A. Typically, fatigue failures are induced by thermal expansion mismatches between the component
14
A and the supporting substrate
24
A. For example, if the component
14
A comprises a first material, such as ceramic having a first CTE, and the supporting substrate
24
A comprises a second material, such as FR-4 having a second CTE, cyclic loads can be placed on the contact ball
10
A as the assembly
22
A is thermally cycled during normal operation.
The forces acting on the contact ball
10
A include tensile forces
30
, moment forces
32
,
34
and shear forces
36
. If these forces are large enough, the contact ball
10
A can separate from the bonding pad
12
A on the component
14
A. This separation can form an electrical open in the electrical path between the contact ball
10
A and the bonding pad
12
A on the component
14
A. This separation also compromises the physical bond between the component
14
A and the supporting substrate
24
A. This problem is compounded because the area of interface between the contact ball
10
A and the bonding pad
12
A is relatively small. The forces are thus concentrated over a relatively small area.
FIGS. 1B-1F
illustrate other types of components in which separation can occur between an external contact and a bonding pad on the component. In
FIG. 1B
, a component
14
B includes a bonding pad
12
B and a contact bump
10
B formed on the bonding pad
12
B. In addition, the contact bump
10
B is bonded directly to a contact pad
28
B on a supporting substrate
24
B. In this example, the contact bump
10
B can be formed on the bonding pad
12
B using a deposition process, such as evaporation of a ball limiting metallurgy (BLM) and solder material through openings in a metal mask. In addition to the contact bump
10
B, the ball limiting metallurgy (BLM) can include a multi layered stack (not shown) such as an adherence layer (e.g., Cr), a solderable layer (e.g., Cu) and a flash layer (e.g., Au). This process is also known as C4 technology, and is typically used to deposit contact bumps
10
B directly onto aluminum bond pads on a semiconductor wafer or die. Alternately, other deposition deposition can be used to form the contact bump
10
B. The contact bumps
10
B can also comprise a pre-formed eutectic ball, which is placed on the contact pad
28
B and reflowed, substantially as previously described for the non-eutectic contact ball
10
A. In this case flux can be employed or reflow can be performed in an inert atmosphere.
In
FIG. 1C
, a component
14
C includes a bonding pad
12
C and a solder contact column
10
C bonded to the bonding pad
12
C using a eutectic solder fillet
16
C. This type of component
14
C is sometimes referred to as a ceramic column grid array (CCGA). The contact column
10
C comprises an elongated member configured for bonding to a contact pad
28
C on a supporting substrate
24
C using a eutectic solder fillet
26
C.
In
FIG. 1D
, a component
14
D includes a TAB contact bump
10
D bonded to a multi layered tape
38
, that is similar to TAB tape. This type of component
14
D is sometimes referred to as a TAB ball grid array (TBGA). For surface mounting the component
14
D, the TAB contact bump
10
D is configured for bonding to a contact pad
28
D on a supporting substrate
24
D using a eutectic solder fillet
26
D.
In
FIG. 1E
, a component
14
E includes a solder mask
40
having an opening
42
in which a solder mask contact ball
10
E is formed. The opening
42
in the solder mask
40
facilitates alignment and bonding of the contact ball
10
E to a bonding pad
12
E on the component
14
E. In addition in the completed assembly, the solder mask
40
insulates the contact ball
10
E from adjacent contact balls
10
E and other electrical elements on the component
14
E, such as conductive traces. F
Farnworth Warren M.
Wood Alan G.
Berezny Nema
Gratton Stephen A.
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