# Patent

## Title
Semiconductor package with trace covered by solder resist

## Abstract

The invention provides a semiconductor package. The semiconductor package includes a substrate. A first conductive trace is disposed on the substrate. A first conductive trace disposed on the substrate. A semiconductor die is disposed over the first conductive trace. A solder resist layer is formed such a portion of the solder resist layer and a portion of the first conductive trace collectively have a T-shaped cross section.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a Continuation of U.S. patent application Ser. No. 14/103,066, filed on Dec. 12, 2013, now U.S. Pat. No. 9,142,526, which is a Continuation of Ser. No. 13/332,658, filed on Dec. 21, 2011, now U.S. Pat. No. 8,633,588, issued on Jan. 21, 2014. The entireties of which are incorporated by reference herein.


BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a semiconductor package, and in particular, to a solder resist layer design of a flip chip package.
Description of the Related Art
For the conventional flip chip package, it is well known that the underfill protects the conductive bumps by considerably reducing the stress to the conductive bumps. However, the underfill itself is subject to shear or peeling stress and consequently, may induce failure modes. For instance, an imperfect underfill with voids or microcracks will produce cracks or delamination under temperature cycling conditions.
Delamination at bimaterial interfaces such as the underfill and conductive traces, driven by coefficient of thermal expansion (CTE) mismatching between organic underfills and inorganic conductive traces, is one of failure modes. Once the underfill delamination, occurs, failure usually results from conductive bump fatigue cracks because of the loss of the underfill protection and stress concentration arising from the underfill delamination.
Thus, a novel flip chip package without the underfill delamination is desirable.
BRIEF SUMMARY OF INVENTION
A semiconductor package is provided. An exemplary embodiment of a semiconductor package includes a substrate. A first conductive trace is disposed on the substrate. A solder resist layer is disposed on the substrate, having an extending portion covering a portion of the first conductive trace, wherein a width of the extending portion of the solder resist layer is larger than that of the portion of the first conductive trace. A semiconductor die is disposed over the first conductive trace.
Another exemplary embodiment of a semiconductor package includes a substrate. A first conductive trace is disposed on the substrate. A solder resist layer is disposed on the substrate, having an extending portion covering a portion of the first conductive trace, wherein the extending portion of the solder resist layer has a vertical sidewall extruding over to an adjacent vertical sidewall of the portion of the first conductive trace. A semiconductor die is disposed over the first conductive trace.
A detailed description is given in the following embodiments with reference to the accompanying drawings.



BRIEF DESCRIPTION OF DRAWINGS
The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:
FIG. 1 shows a top view of one exemplary embodiment of a semiconductor package of the invention.
FIG. 2 shows a cross section along line A-A′ of FIG. 1.
FIG. 3 shows a cross section along line B-B′ of FIG. 1.
FIG. 4 shows a top view of another exemplary embodiment of a semiconductor package of the invention.
FIG. 5 shows a cross section along line A-A′ of FIG. 4.
FIG. 6 shows a cross section along line B-B′ of FIG. 4.



DETAILED DESCRIPTION OF INVENTION
The following description is a mode for carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. Wherever possible, the same reference numbers are used in the drawings and the descriptions to refer the same or like parts.
The present invention will be described with respect to particular embodiments and with reference to certain drawings, but the invention is not limited thereto and is only limited by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn to scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual dimensions to practice of the invention.
FIG. 1 shows a top view of one exemplary embodiment of a semiconductor package 500a of the invention. FIG. 2 shows a cross section along line A-A′ of FIG. 1. FIG. 3 shows a cross section along line B-B′ of FIG. 1. One exemplary embodiment of a semiconductor package 500a is a flip chip package using copper pillars connecting a semiconductor die and a substrate. As shown in FIGS. 1-3, one exemplary embodiment of a semiconductor package 500a comprises a substrate 200 with first conductive traces 204 and second conductive traces 202 disposed thereon. In one embodiment, the substrate 200 may be formed of by semiconductor materials such as silicon, or organic materials such as bismaleimide triacine, (BT), polyimide or ajinomoto build-up film (ABF). In one embodiment, the first conductive trace 204 and the second conductive trace 202 may comprise signal traces or ground traces, which are used for input/output (I/O) connections of a semiconductor die 210 mounted directly onto the substrate 200. In this embodiment, each of the first conductive traces 204 serves as a signal/ground trace segment for routing, and each of the second conductive traces 202 has a portion 202a as a pad region of the substrate 200.
Next, still referring to FIGS. 1-3, a solder resist layer 206 is conformably formed covering the substrate 200 by a deposition method and then the solder resist layer 206 is subjected to a patterning process. After the patterning process, the solder resist layer 206, except for extending portions 208, exposes an overlapping region between a subsequently mounted semiconductor die 210 and the substrate 200. It is noted that the extending portions 208 of the solder resist layer 206 extends along the first conductive trace 204 and covering a portion of the first conductive trace 204. Also, the solder resist layer 206, except for extending portions 208, is disposed away from the subsequently mounted semiconductor die 210 by a distance d1. In one embodiment, the solder resist layer 206 may comprise solder mask materials, oxide, nitride, or oxynitride. As shown in FIG. 2, the extending portions 208 of the solder resist layer 206 covers a portion 204a of the first conductive trace 204. It is noted that a width W2 of the extending portion 208 of the solder resist layer 206 is designed to be larger than a width W1 of the portion 204a of the first conductive trace 204, so that a portion of a bottom surface 209 of the extending portion 208 of the solder resist layer 206 is exposed from the 204a of the first conductive trace 204, and the extending portion 208 of the solder resist layer 206 has a vertical sidewall 207 extruding over to an adjacent vertical sidewall 205 of the portion 204a of the first conductive trace 204. Therefore, the extending portion 208 and the portion 204a of the first conductive trace 204 collectively have a T-shaped cross section.
Next, a dry film photoresist or a liquid photoresist (not shown) is entirely laminated on the substrate 200. Next, the dry film photoresist/liquid photoresist is patterned by a photolithography process comprising an exposure step and a development step to form openings (not shown) respectively over the portions (pad regions) 202a of the second conductive traces 202, so that formation positions of a subsequently formed conductive pillar may be defined.
Then, the conductive pillars 212 are respectively formed on the portions (pad regions) 202a of the second conductive traces 202, filling the openings of the dry film photoresist/liquid photoresist. Alternatively, conductive buffer layers (not shown) formed of Ni may be formed between the conductive pillars 212 and the portions (pad regions) 202a of the second conductive traces 202, and the conductive buffer layers may serve as seed layers, adhesion layers and barrier layers for the conductive pillars 212 formed thereon. In one embodiment, the conductive pillars 212 are used as a solder joint for a subsequently formed conductive bump, which transmits input/output (I/O), ground or power signals of the semiconductor die 210, formed thereon. Therefore, the conductive pillars 212 may help to increase the mechanical strength of the bump structure. In one embodiment, the conductive pillars 212 may be formed of copper. Next, the dry film photoresist/liquid photoresist is removed by a stripping process such as a wet etching process using a suitable etchant.
Next, still referring to FIGS. 1-3, the semiconductor die 210 has a plurality of conductive bumps 214 formed on bond pads (not shown) of the semiconductor die 210 mounted on the substrate 200. The conductive bumps 214 respectively connect to the portions (pad regions) 202a of the second conductive traces 202 through the conductive pillars 212 therebetween. As shown in FIG. 1, the solder resist layer 206 is disposed away from the portions (pad regions) 202a of the second conductive traces 202, which overlap with the conductive pillars 212, by at least a distance d2. As shown in FIG. 3, the extending portion 208 of the solder resist layer 206 is below the semiconductor die 210, over a bottom surface 224 of the semiconductor die 210 and within a projection area 222 of the semiconductor die 210.
Next, referring to FIGS. 2-3, an underfill material 220 may flow to fill a gap between the substrate 200 and the semiconductor die 210 and cover the solder resist layer 206 via capillary action by a dispensing method to compensate for differing coefficients of thermal expansion (CTE) between the substrate, the conductive traces and the semiconductor die. The underfill material 220 is then cured. In one embodiment of the invention, the portion of the bottom surface 209 of the extending portion 208 of the solder resist layer 206 is wrapped by the underfill material 220. After the aforementioned processes, one exemplary embodiment of a semiconductor package 500a is completely formed.
FIG. 4 shows a top view of one exemplary embodiment of a semiconductor package 500b of the invention. FIG. 5 shows a cross section along line A-A′ of FIG. 4. FIG. 6 shows a cross section along line B-B′ of FIG. 4. One exemplary embodiment of a semiconductor package 500b is a flip chip package using solder bumps but not copper pillars for a connection between a semiconductor die and a substrate. As shown in FIGS. 4-6, one exemplary embodiment of a semiconductor package 500b comprises a substrate 300 with first conductive traces 304 and second conductive traces 302 disposed thereon. In one embodiment, the substrate 300 may be formed of by semiconductor materials such as silicon, or organic materials such as bismaleimide triacine, (BT), polyimide or ajinomoto build-up film (ABF). In one embodiment, the first conductive trace 304 and the second conductive trace 302 may comprise signal traces or ground traces, which are used for input/output (I/O) connections of a semiconductor die 310 mounted directly onto the substrate 300. In this embodiment, each of the first conductive traces 304 serves as a signal/ground trace segment for routing, and each of the second conductive traces 302 has a portion 302a as a pad region of the substrate 300.
Next, still referring to FIGS. 4-6, a solder resist layer 306 is conformably formed covering the substrate 300 by a deposition method and then the solder resist layer 306 is subjected to a patterning process. After the patterning process, the solder resist layer 306, except for extending portions 308, exposes an overlapping region between a subsequently mounted semiconductor die 310 and the substrate 300. It is noted that the extending portions 308 of the solder resist layer 306 extends along the first conductive trace 304 and covering a portion of the first conductive trace 304. Also, the solder resist layer 306, except for extending portions 308, is disposed away from the subsequently mounted semiconductor die 310 by a distance d1. In one embodiment, the solder resist layer 306 may comprise solder mask materials, oxide, nitride, or oxynitride. As shown in FIG. 5, the extending portions 308 of the solder resist layer 306 covers a portion 304a of the first conductive trace 304. It is noted that a width W2 of the extending portion 308 of the solder resist layer 306 is designed to be larger than a width W1 of the portion 304a of the first conductive trace 304, so that a portion of a bottom surface 309 of the extending portion 308 of the solder resist layer 306 is exposed from the 304a of the first conductive trace 304, and the extending portion 308 of the solder resist layer 306 has a vertical sidewall 307 extruding over to an adjacent vertical sidewall 305 of the portion 304a of the first conductive trace 304. Therefore, the extending portion 308 and the portion 304a of the first conductive trace 304 collectively have a T-shaped cross section.
Next, referring to FIGS. 4-6, a solder printing process is performed to form solder paste patterns (not shown) on the portions (pad regions) 302a of the second conductive traces 302. Next, a semiconductor die 310 having a plurality bond pads (not shown) is mounted on the substrate 300. Bond pads (not shown) of the semiconductor die 310 respectively connect the solder paste patterns. Next, a reflow process and a cooling process are performed in sequence, so that the solder paste patterns are transformed into solder bumps 312 connecting the portions (pad regions) 302a of the second conductive traces 302 of the substrate 300 and the bond pads (not shown) of the semiconductor die 310. As shown in FIG. 4, the solder resist layer 306 is disposed away from the portions (pad regions) 302a of the second conductive traces 302, which overlap with the solder bumps 312, by at least a distance d2. As shown in FIG. 6, the extending portion 308 of the solder resist layer 306 is below the semiconductor die 310, over a bottom surface 324 of the semiconductor die 310 and within a projection area 322 of the semiconductor die 310.
Next, referring to FIGS. 5-6, an underfill material 320 may flow to fill a gap between the substrate 300 and the semiconductor die 310 and cover the solder resist layer 306 via capillary action by a dispensing method to compensate for differing coefficients of thermal expansion (CTE) between the substrate, the conductive traces and the semiconductor die. The underfill material 320 is then cured. In one embodiment of the invention, the portion of the bottom surface 309 of the extending portion 308 of the solder resist layer 306 is wrapped by the underfill material 320. After the aforementioned processes, another exemplary embodiment of a semiconductor package 500b is completely formed.
Some advantages of exemplary embodiments of a semiconductor package 500a and 500b of the invention are described in the following. The underfill material wraps the portion of the bottom surface of the extending portion of the solder resist layer, which has a wider width than the portion of the first conductive trace, so that the underfill material may be anchored with a T-shaped feature formed by both the extending portion of the solder resist layer and the portion of the first conductive trace. Thus, the conventional underfill delamination problem occurring between the conductive trace and the underfill material is improved. Also, the extending portion of the solder resist layer only extends into a projection area of the die to cover a portion of the first conductive trace, and the remaining portion of the solder resist layer is disposed away from the semiconductor die by a distance, so that the semiconductor package still has enough space to allow the underfill material to flow to fill the gap between the substrate and the semiconductor die. Therefore, the extending portion of the solder resist layer does not affect the performance of the dispensing process. Moreover, exemplary embodiments of a semiconductor package can be used in many types of package methods. For example, a gap between the substrate and the semiconductor die can be filled with a molding compound only. Alternatively, the gap between the substrate and the semiconductor die can be filled with a molding compound and an underfill material. Further, the gap between the substrate and the semiconductor die can be filled with an underfill material only.
While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.

## Claims

1. A semiconductor package, comprising:
a substrate;
a plurality of first conductive traces disposed on the substrate;
a semiconductor die disposed over the plurality of first conductive traces; and
a solder resist layer patterned such that portions of the solder resist layer are removed over an overlapping area between the semiconductor die and the substrate such that each of the plurality of first conductive traces exhibits a covered portion, covered by the patterned solder resist layer, and an uncovered portion, not covered by the patterned solder resist layer,
wherein portions of the patterned solder resist layer directly overlie and cover corresponding portions of the plurality of first conductive traces,
wherein each overlying portion of the patterned solder resist layer exhibits a width extending from a first resist side wall to a second resist side wall, and each of the first conductive traces exhibits a width extending between a first trace side wall and a second trace side wall, and the width of each overlying portion of the patterned solder resist layer is wider than the width of the corresponding one of the first conductive traces over which the portion overlies, such that each overlying portion of the patterned solder resist layer and the corresponding one of the first conductive traces together exhibit a T-shaped cross section, from a side view perspective, and
wherein, in plan view, the plurality of first conductive traces extend inwardly toward the semiconductor die from multiple directions.

2. The semiconductor package as claimed in claim 1, wherein the portions of the solder resist layer are below the semiconductor die and within a projection area of the semiconductor die.

3. The semiconductor package as claimed in claim 1, wherein each portion of the patterned solder resist layer has a vertical sidewall extruding over to an adjacent vertical sidewall of the portion of the first conductive trace from a top view perspective.

4. The semiconductor package as claimed in claim 1, wherein each portion of the solder resist layer extends along the first conductive trace and over a bottom surface of the semiconductor die.

5. The semiconductor package as claimed in claim 1, wherein each portion of the solder resist layer extends from outside an edge of the semiconductor die to a region between the semiconductor die and the substrate.

6. The semiconductor package as claimed in claim 1, further comprising:
an underfill material filling a gap between the substrate and the semiconductor die.

7. The semiconductor package as claimed in claim 6, wherein each portion of the solder resist layer is covered by the underfill material.

8. The semiconductor package as claimed in claim 1, wherein a plurality of strips of the solder resist layer extend from outside an edge of the semiconductor die to a region between the semiconductor die and the substrate.

9. The semiconductor package as claimed in claim 1, wherein the substrate is formed by bismaleimide triacine (BT), polyimide or ajinomoto build-up film (ABF).

10. A semiconductor package, comprising:
a substrate;
a plurality of first conductive traces disposed on top of the substrate;
a plurality of second conductive traces disposed on top of the substrate;
a semiconductor die disposed over the plurality of first conductive traces;
a solder resist layer patterned such that portions of the solder resist layer are removed over an overlapping area between the semiconductor die and the substrate such that each of the plurality of first conductive traces exhibits a covered portion, covered by the patterned solder resist layer, and an uncovered portion, not covered by the patterned solder resist layer,
wherein each covering portion of the solder resist layer exhibits a width extending from a first resist side wall to a second resist side wall, and each of the first conductive traces exhibits a width extending between a first trace side wall and a second trace side wall, and the width of each covering of the solder resist layer is wider than the width of the corresponding one of the first conductive traces over which the portion covers, such that each covering of the solder resist layer and the corresponding one of the first conductive traces together exhibit a T-shaped cross section, from a side view perspective,
wherein the first and second conductive traces are not conductively connected, and
wherein, in plan view, the plurality of first conductive traces extend inwardly toward the semiconductor die from multiple directions.

11. The semiconductor package of claim 10, wherein the patterned portions of the solder resist layer extend from outside an edge of the semiconductor die to a region between the semiconductor die and the substrate.

12. The semiconductor package as claimed in claim 10, wherein at least one of the covering portions of the solder resist layer extends across an edge of the semiconductor die.

13. The semiconductor package as claimed in claim 10, further comprising:
an underfill material filling a gap between the substrate and the semiconductor die.

14. The semiconductor package as claimed in claim 13, wherein the portions of the solder resist layer are covered by the underfill material.

15. The semiconductor package as claimed in claim 10, wherein a plurality of strips of the solder resist layer extend from outside an edge of the semiconductor die to a region between the semiconductor die and the substrate.

16. The semiconductor package as claimed in claim 10, wherein the portions of the solder resist layer are below the semiconductor die and within a projection area of the semiconductor die.

17. The semiconductor package as claimed in claim 10, wherein conductive bumps of the semiconductor die respectively connect to corresponding portions of the second conductive trace through conductive pillars therebetween.

18. The semiconductor package as claimed in claim 10, wherein the substrate is formed by bismaleimide triacine (BT), polyimide or ajinomoto build-up film (ABF).