FIELD OF THE INVENTION
This invention relates to a chip-on-film (COF) package, and more particularly to a COF package in which a chip is bonded to a substrate using a composite bump.
BACKGROUND OF THE INVENTION
Conventionally, in order to obtain a COF package, a higher bonding force is required for bonding bumps on a chip to leads on a substrate. Bump pitch is reduced owing to chip output ports are increased significantly, but bumps may be compressed to be connected to the adjacent one and cause short circuit during bonding process. Otherwise, reliability of the conventional COF package is lower because bonding strength between the bumps and the leads is insufficient.
SUMMARY
One object of the present invention is to provide a COF package in which composite bumps on a chip are provided to be bonded to leads on a substrate.
A COF package of the present invention includes a substrate and a chip, the substrate includes a plurality of leads, and the chip includes a body, a plurality of bond pads, a protective layer and a plurality of composite bumps. The bond pads are arranged on the body, a surface of the body is covered by the protective layer, the protective layer includes openings configured to expose the bond pads. Each of the composite bumps includes a first raising strip, a UBM layer and a bonding layer, the first raising strip is located on the protective layer and covered by the UBM layer, the UBM layer is electrically connected to the bond pad, covered by the bonding layer and includes a first rib located on the first raising strip. The bonding layer includes a first bonding rib located on the first rib along a first direction parallel to the surface of the body, the first bonding rib is inserted into the lead to allow the lead to generate a first restricted rib located above the bond pad.
Because of the first raising strip arranged on the protective layer, the compressive strength of the chip can be improved, and the first bonding rib can be inserted into the lead in the flip-chip bonding process to reduce the force required for bonding the chip to the substrate. After inserting into the lead, the first bonding rib can surface-contact with the lead to increase weld length of the bonding layer and the lead and increase bonding strength between the chip and the substrate.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective exploded diagram illustrating a COF package in accordance with one embodiment of the present invention.
FIG. 2 is a cross-section view diagram illustrating a COF package in accordance with one embodiment of the present invention.
FIG. 3 is a cross-section view diagram illustrating a chip of a COF package in accordance with one embodiment of the present invention.
FIG. 4 is a cross-section view diagram along I-I line of FIG. 3.
FIG. 5 is a cross-section view diagram along J-J line of FIG. 3.
FIG. 6 is a cross-section view diagram along K-K line of FIG. 3.
FIG. 7 is a perspective diagram illustrating a chip of a COF package in accordance with another embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
With reference to FIGS. 1 and 2, a COF package 100 in accordance with one embodiment of the present invention includes a substrate 110 and a chip 120. In a flip-chip bonding process, a plurality of composite bumps 124 on the chip 120 are bonded to a plurality of leads 111 on the substrate 110 to obtain the COF package 100. Preferably, a underfill material (not shown) is provided between the substrate 110 and the chip 120 and it may be a non-conductive film (NCF). The composite bumps 124 and the leads 111 are fully covered by the underfill material to avoid oxidation.
With reference to FIGS. 1 to 3, the chip 120 includes a body 121, a plurality of bond pads 122, a protective layer 123 and the composite bumps 124 mentioned above. The bond pads 122 are arranged on the body 121, the protective layer 123 covers a surface 121a of the body 121 and includes a plurality of openings 123a, the bond pads 122 are visible from the openings 123a one by one.
With reference to FIGS. 1 and 3, each of the composite bumps 124 includes a first raising strip A, a under bump metallization (UBM) layer C and a bonding layer D, and preferably, each of the composite bumps 124 further includes at least one second raising strip B. The first raising strip A and the second raising strip B, which may be made of polymer material, are arranged on the protective layer 123, and the first raising strip A is located between the opening 123a of the protective layer 123 and the second raising strip B. Referring to FIG. 3, there is a first gap G1 located between the first raising strip A and the second raising strip B, and in this embodiment, there is further a second gap G2 located between the first raising strip A and the opening 123a of the protective layer 123. The protective layer 123 is visible in the first gap G1 and the second gap G2.
With reference to FIGS. 1, 4 and 5, along a first direction X parallel to the surface 121a of the body 121, each of the openings 123a of the protective layer 123 has a first width W1 and the first raising strip A has a second width W2. Preferably, the second width W2 is greater than or equal to the first width W1. With reference to FIGS. 1, 4 and 6, the second raising strip B has a fifth width W5 in the first direction X, and preferably, the fifth width W5 is greater than or equal to the first width W1 of the opening 123a. A chip 120 in accordance with another embodiment of the present invention is shown in FIG. 7, and in this embodiment, the first raising strips A of the adjacent composite bumps 124 are connected with each other to become a longer raising strip, and the second raising strips B of the adjacent composite bumps 124 are connected with each other to become another longer raising strip. The first raising strips A connected mutually and the second raising strips B connected mutually can increase the compressive strength of the chip 120 to prevent the chip 120 from breaking during the flip-chip bonding process, and further can increase a height of the bonding layer D.
With reference to FIGS. 1 to 3, the UBM layer C covers the first raising strip A, the second raising strip B and the protective layer 123 visible in the first gap G1, and in this embodiment, the UBM layer C further covers the protective layer 123 visible in the second gap G2. The UBM layer C includes a first rib C1 formed on the first raising strip A, a second rib C2 formed on the second raising strip B and a groove C3 located between the first raising strip A and the second raising strip B, the groove C3 is located between the first rib C1 and the second rib C2. The UBM layer C is electrically connected to the bond pad 122, and in this embodiment, the UBM layer C covers the bond pad 122. The UBM layer C may be a single metal layer or multiple metal layers, and may be made of titanium (Ti), tungsten titanium (TiW), copper (Cu), nickel (Ni), gold (Au) or nickel vanadium (NiV).
With reference to FIGS. 1 to 3, the bonding layer D covers the UBM layer C and includes a first bonding rib D1 formed on the first rib C1, a second bonding rib D2 formed on the second rib C2 and a restriction groove D3 located within the groove C3 along the first direction X, the restriction groove D3 is located between the first bonding rib D1 and the second bonding rib D2. In this embodiment, the bonding layer D covers the UBM layer C located in the opening 123a of the protective layer 123, and it may be made of gold (Au), copper (Cu), tin (Sn), gold/tin alloy (Au/Sn), tin-silver alloy (Sn/Ag), indium (In), bismuth/tin alloy (Bi/Sn) or tin/lead alloy (Sn/Pb).
With reference to FIGS. 1 and 3, in a second direction Y vertical to the surface 121a of the body 121, the height from a terminal A1 of the first raising strip A to the surface 121a of the body 121 is referred as a first height H1, and the height from a terminal D4 of the bonding layer D located over the bond pad 122 to the surface 121a of the body 121 is referred as a second height H2 which is less than the first height H1. In this embodiment, the height from a terminal B1 of the second raising strip B to the surface 121a of the body 121 in the second direction Y is referred as a third height H3 which is substantially equal to the first height H1.
With reference to FIGS. 1, 5 and 6, the UBM layer C located on the first raising strip A and the second raising strip B has a third width W3 in the first direction X, and the third width W3 of the UBM layer C is less than or equal to the second width W2 of the first raising strip A and is less than or equal to the fifth width W5 of the second raising strip B. The bonding layer D located on the first rib C1 and the second rib C2 has a fourth width W4 in the first direction X, and the fourth width W4 of the bonding layer D is greater than or equal to the third width W3 of the UBM layer C.
With reference to FIGS. 1 to 3, the first bonding rib D1 on the composite bump 124 is designed to be inserted into the lead 111 during the flip-chip bonding process such that the chip 120 can be electrically connected to the substrate 110. And in this embodiment, the first bonding rib D1 and the second bonding rib D2 on the composite bump 124 are inserted into the lead 111 to allow the chip 120 to be electrically connected to the substrate 110. Owing to the first height H1 of the first raising strip A is higher than the second height H2 of the bonding layer D located above the bond pad 122 and substantially equal to the third height H3 of the second raising strip B, a first restricted rib 111a located above the bond pad 122 and a second restricted rib 111b located within the restriction groove D3 are formed on the lead 111. The second restricted rib 111b is restricted between the first bonding rib D1 and the second bonding rib D2 and can increase the bonding strength of chip 120 to the substrate 110 to avoid the chip 120 from separating from the substrate 110.
With reference to FIGS. 1 to 3, the first raising strip A and the second raising strip B on the protective layer 123 are provided to increase the compression strength of the chip 120 and protect the chip 120 from breaking during the flip-chip bonding process. The first bonding rib D1 and the second bonding rib D2 generated by the first raising strip A, the second raising strip B, the UBM layer C and the bonding layer D can be inserted into the lead 111 during the flip-chip bonding process, thus the force applied on the chip 120 and the substrate 110 for bonding can be reduced to avoid the compressed bumps from expanding outwardly to connect with the adjacent one and cause short circuit during the flip-chip bonding process.
The first bonding rib D1 and the second bonding rib D2 inserting into the lead 111 can surface-contact with the lead 111 to increase weld length of the bonding layer D and the lead 111 and increase bonding strength between the chip 120 and the substrate 110.
While this invention has been particularly illustrated and described in detail with respect to the preferred embodiments thereof, it will be clearly understood by those skilled in the art that is not limited to the specific features shown and described and various modified and changed in form and details may be made without departing from the scope of the claims.
Patent Application
20230326896
