Adhesion enhanced semiconductor die for mold compound packaging

Abstract

A semiconductor die includes a metal layer deposited thereon for enhancing adhesion between the die and a mold compound package. The metal layer is substantially oxide free. The die is coated with a layer or layers of copper (Cu) and/or palladium (Pd) by electroplating or electroless coating techniques. The metal layer provides a uniform wetting surface for better adhesion of the die with the mold compound package during encapsulation. The increased adhesion reduces the delamination potential of the die from the package.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates in general to a semiconductor die packaging technique and, more particularly, to a die having a metal layer back side for enhanced adhesion of the die in a Leads On Chip (LOC) package system.

2. Background of Related Art

A semiconductor integrated circuit (IC) packaged device generally includes an IC chip (die) being connected to inner leads of a lead frame by wire bonds. The chip, wire bonds, and inner leads are completely encapsulated (packaged) for protection with a substance, such as plastic. Outer leads communicate with the inner leads of the lead frame, but the outer leads typically remain exposed for mounting of the packaged device to external circuitry, such as a printed circuit board. Conventionally, encapsulation occurs by a transfer molding technique wherein the encapsulation substance is a thermoset epoxy molded around and to the die and lead frame and subsequently cured.

In a conventional IC packaged device, a semiconductor die is placed on and bonded to a center die paddle of a lead frame for support. Inner lead fingers of the lead frame approach the paddle but do not contact or communicate with the paddle. Rather, wire bonds communicate between contact pads on the die and the inner lead fingers of the lead frame by spanning the gap between the die and the fingers. The wire bonds allow for the transmission of the electrical signals to and from the die and the lead frame.

However, to shrink the conventional packaging requirements, techniques such as the Lead On Chip (LOC) method have been developed. The LOC technique disposes the inner lead fingers of a lead frame directly over the die (or IC chip) rather than away from the die. Double-sided adhesive insulating tape attaches the conductive lead fingers to the die so that no gap exists between the die and lead fingers. Wire bonds communicate between the contact pads on the die and the inner lead fingers which are disposed over the insulating tape directly over a portion of the die adjacent the die pads.

This LOC technique allows the entire packaging of the IC device to be smaller because the inner lead fingers are disposed directly over the die rather than separate from the die. Similar to the LOC technique, other variations of using an adhesive tape for adhering lead fingers and, consequently, shrinking packaging requirements include a Tape Under Frame technique and a Leads Under Die method.

Although IC packaging is minimized in each of these packaging techniques that uses an adhesive tape, other problems surface. One such problem in the LOC technique is the difficulty of obtaining a good, solid adhesive bond between the die and the package. One reason a solid bond is not achieved is because the oxide on the silicon die substrate does not lend itself to uniform wetting, which is necessary for good adhesion with the liquid mold compound.

When a die does not bond well with the mold compound package, delamination may occur and the device may potentially be ruined during the manufacturing process or surface mount of the package. Since production environment areas retain a substantial humidity level to reduce static buildup, i.e., often about 50%, moisture absorbs into the mold compound and can penetrate delaminated areas between the die and mold compound. When the moisture is converted to steam from heat processes and the steam pressure is greater than the strength of the adhesion couple between the mold compound and the die, the mold compound will crack or explode with a “popcorn” effect.

To overcome this potential package cracking problem, one technique has been to bake the moisture out of the mold compound to ensure a low moisture content within the package. Another step is to place the device in a “dry package” for shipping purposes by placing the final semiconductor chip product in a shipping container with a desiccant drying agent, such as silica gel. Although these techniques are commonly used in the semiconductor industry, they provide only a temporary solution. Namely, when a semiconductor manufacturer ships a “dried” packaged device by following these techniques, the device may still absorb moisture at a customer's site after the device is removed from the shipping container materials. Furthermore, if the die has delaminated even slightly, the package is subject to moisture penetration again and the package may subsequently crack if exposed to sufficient heat.

Another technique for reducing delamination potential is disclosed in U.S. Pat. No. 5,227,661 issued to Heinen on Jul. 13, 1993. Although this method provides a working solution, it retains disadvantages by its use of aminopropyltriethox-silane as a coating on the die.

Obviously, the foregoing problems and solutions associated with providing a good bond between a die and a die package to avoid delamination and cracking of the package are undesirable aspects of conventional semiconductor packaging techniques. Accordingly, objects of the present invention are to provide an improved bonding between a semiconductor die and its encapsulating package in order to decrease delamination potential of the die from the package.

SUMMARY OF THE INVENTION

According to principles of the present invention in its preferred embodiment, a back side of a semiconductor die includes a metal layer deposited thereon for enhancing adhesion between the die and a mold compound package. The metal layer is substantially oxide free. The die is coated with a layer or layers of copper (Cu) and/or palladium (Pd) by electroplating or electroless coating techniques.

According to further principles of the present invention, the metal layer preferably comprises approximately 50 micro inches of a Cu layer deposited over the back side of the die and approximately 2 to 3 micro inches of a Pd layer deposited over the Cu layer.

Advantageously, the metal layer on the die provides a uniform wetting surface for better adhesion of the die with the mold compound during encapsulation. The increased adhesion reduces delamination potential of the die from the package and, consequently, reduces cracking of the package.

The aforementioned principles of the present invention provide an adhesion enhanced semiconductor die for improving adhesion of the die with a mold compound packaging. Other objects, advantages, and capabilities of the present invention will become more apparent as the description proceeds.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is an end-section view of a packaged integrated circuit die having the present invention adhesion enhanced layer deposited thereon; and

FIG. 2 is an enlarged partial view of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is an end-section view of packaged integrated circuit (IC) 10. Lead frame 15 is disposed over IC die 20, the lead frame including inner and outer lead finger portions 25 and 30, respectively. Inner lead finger portions 25 are adjacent die pads 35, and outer lead finger portions 30 extend outward of mold compound packaging 40 for connection with appropriate external circuitry.

Insulator adhesive tape strips 45 are disposed between inner lead finger portions 25 and frontside 50 of die 20 to adhere the lead finger portions to the die. Integrated circuitry is disposed on frontside 50 of die 20. Wire bonds 52 communicate between inner lead finger portions 25 and die pads 35 for making the electrical connection between the die and the lead finger portions.

Metal layer 55 is shown deposited over back side 60 of die 20. Metal layer 55 enhances adhesion of die 20 with mold compound packaging 40. Metal layer 55 is deposited over die 20 using an electroplating process or electroless coating process well known in the art prior to packaging the die with mold compound packaging 40.

Metal layer 55 provides a uniform wetting surface for mold compound packaging 40 to adhere better to die 20. Although shown in its hardened and cured state, mold compound packaging 40 is in a flowing state when it is initially heated over and molded around die 20. Consequently, the uniform wetting surface provided by metal layer 55 enhances the adhesion between the die and the mold compound packaging.

In its preferred embodiment, metal layer 55 is substantially oxide free. Also, preferably, the metal layer is either palladium (Pd) or copper (Cu), or a combination thereof, although it is obvious other metals may likewise suffice. Although copper is cheaper in cost, it retains more oxide which counteracts the intended adhesion. Palladium is more expensive, but provides a substantially oxide-free layer for effectuating a good bond with the mold compound.

Although a single metal layer suffices to provide the advantages of the present invention, in its preferred embodiment, metal layer 55 actually comprises a plurality of layers as shown in FIG. 2. Namely, a cheaper, thicker layer 65 of copper deposited over back side 60 of die 20 provides a good barrier to the oxide on die 20. A thinner layer 70 of palladium is deposited over the copper layer 65 to provide an even more uniform wetting surface. The palladium is also substantially free from oxide. Preferably, about 50 micro inches of copper and approximately 2 to 3 micro inches of palladium are deposited. Consequently, this combination of metal layers provides the enhanced adhesion metal layer 55 on die 20 and, together, provides a good balance of cost and effectiveness.

As previously mentioned, when a die does not bond well with the mold compound package, delamination may occur and the device may potentially be ruined during the manufacturing process or surface mount of the package because of moisture penetration between the die and compound. When the moisture is converted to steam from heat processes and the steam pressure is greater than the strength of the adhesion couple between the mold compound package and the die, the mold compound package will crack or explode with a “popcorn” effect.

The present invention, as described and diagramed, reduces this potential package cracking problem. Consequently, no baking of the moisture out of the mold compound package is needed, and no “dry packaging” the device for shipping purposes is needed.

What has been described above are the preferred embodiments for a semiconductor die having a metal layer back side for enhancing adhesion between the die and its mold compound packaging. It is clear that the present invention provides a powerful tool for reducing delamination potential of a die and subsequent cracking of the mold compound packaging. While the present invention has been described by reference to specific embodiments, it will be apparent that other alternative embodiments and methods of implementation or modification may be employed without departing from the true spirit and scope of the invention.

Claims

1. A semiconductor device encapsulation method, comprising: providing at least a portion of a back surface of a die with at least one substantially oxide-free metal in contact with the portion; and applying packaging material to at least a portion of the at least one substantially oxide-free metal, the at least one substantially oxide-free metal enhancing adhesion of the packaging material to at least the portion.

2. The method of claim 1, wherein providing comprises electroplating.

3. The method of claim 1, wherein providing comprises electroless coating.

4. The method of claim 1, wherein providing comprises providing a plurality of materials on at least the portion, an outermost material of which comprises a substantially oxide-free metal.

5. The method of claim 4, wherein providing comprises: providing at least the portion with copper; and providing palladium over the copper.

6. The method of claim 1, wherein providing comprises providing at least one of copper and palladium on at least the portion.

7. The method of claim 1, wherein providing comprises providing the at least one substantially oxide-free metal over an entirety of the back surface of the die.

8. The method of claim 7, wherein applying is effected over at least the portion of the back surface bearing the at least one substantially oxide-free metal.

9. A semiconductor device encapsulation method, comprising: providing at least a portion of a back surface of a die with at least one substantially oxide-free metal, the at least one substantially oxide-free metal contacting at least the portion; and covering at least the portion of the back surface of the die with a packaging material, the packaging material being wettable with respect to the at least one substantially oxide-free metal.

10. The method of claim 9, wherein providing comprises electroplating.

11. The method of claim 9, wherein providing comprises electroless coating.

12. The method of claim 9, wherein providing comprises providing a plurality of materials, an outermost of which comprises the at least one substantially oxide-free metal.

13. The method of claim 9, wherein providing includes: providing the portion of the back surface of the die with copper; and providing palladium over the copper.

14. The method of claim 9, wherein providing comprises providing at least the portion with at least one of palladium and copper.

15. A method for enhancing adhesion of a packaging material to a semiconductor die, comprising: providing at least a portion of a back surface of a semiconductor die with a first metal, the first metal contacting at least the portion of the back surface; providing a substantially oxide-free metal over the first metal, the substantially oxide-free metal providing a wetting surface to enhance adhesion of a packaging material to at least the portion of the back surface; and adhering the packaging material to at least the substantially oxide-free metal.

16. The method of claim 15, wherein at least one of providing at least the portion of the back surface of the semiconductor die with the first metal and providing the substantially oxide-free metal comprises electroplating.

17. The method of claim 15, wherein at least one of providing at least the portion of the back surface of the semiconductor die with the first metal and providing the substantially oxide-free metal comprises electroless coating.

18. The method of claim 15, wherein providing at least the portion of the back surface of the semiconductor die with the first metal comprises disposing a substantially oxide-free metal.

19. The method of claim 18, wherein providing at least the portion of the back surface of the semiconductor die with the first metal comprises disposing copper.

20. The method of claim 15, wherein providing the substantially oxide-free metal comprises disposing palladium.

21. A semiconductor device configured for enhanced adhesion to packaging material comprising: an active surface carrying integrated circuitry; a back surface opposite the active surface; at least one substantially oxide-free metal in contact with at least a portion of the back surface; and packaging material adjacent to at least a portion of the at least one substantially oxide-free metal.

22. The semiconductor device of claim 21, further comprising: leads secured in place relative to a remainder of the semiconductor device.

23. The semiconductor device of claim 22, wherein the leads are secured directly to the remainder of the semiconductor device in a leads-over-chip arrangement.

24. The semiconductor die of claim 21, wherein the packaging material comprises a plastic molding material.

25. The semiconductor die of claim 24, wherein the plastic molding material comprises a thermoset epoxy material.

26. The semiconductor die of claim 21, wherein the at least one substantially oxide-free metal comprises palladium or copper.

27. The semiconductor die of claim 21, wherein the at least one substantially oxide-free metal comprises a plurality of metals.

28. The semiconductor die of claim 27, wherein at least one metal of the plurality of metals comprises palladium or copper.