Patent Application
20060228878
A claim of priority under 35 U.S.C. §119 is made to Korean Patent Application No. 2005-28594, filed on Apr. 6, 2005; the entire contents of which are incorporated herein by reference.
1. Field of the Invention
Example embodiments of the present invention generally relate to a semiconductor packaging. More particularly, example embodiments of the present invention relate to a package repair method using a lower-melting-point solder.
2. Description of the Related Art
Advancements in the multimedia and digital technologies have allowed electronic products to become smaller, lighter, faster, and/or more efficient. In addition, the electronic products operate at higher speeds with multiple functions. Accordingly, semiconductor products have advanced toward I/O pins having more pins and finer pitch. Ball grid array (BGA) packages using solder balls have been used to meet such advancements.
Semiconductor module products, for example a memory module, may include a module substrate and a plurality of semiconductor packages mounted on one or more surfaces of the module substrate. After packaging, the semiconductor module products may be tested. A specific package that is determined to be faulty during an electrical testing may be replaced with a replacement package. During a repair process, incomplete or excessive melting of solder balls may cause electrical connection problems. Further, heat used during the repair process may negatively influence solder balls of adjacent packages.
Methods of repairing and re-balling a BGA package have been suggested by the present inventors. When a replacement package is attached to a substrate, solder balls of the replacement package may be initially soldered with heat about 450° C. for about 20 seconds, and a final soldered may be performed by a reflow process with heat between about 220° C. and 230° C. for about 80 seconds. The reflow process allows uniform melting of the solder balls. Heat sinks may be used to cover adjacent packages to protect the solder balls from the heat. However, the method cannot be easily applied to a BGA stack package.
Referring to
If a single unit package is found to be faulty, the entire stack package 12 including the faulty unit package may be replaced with a replacement stack package. Heat may be applied to the stack package 12 to separate it from the module substrate 10. Heat sinks may be used to cover adjacent stack packages 12 to protect them from the heat. However, the heat sink may not completely resolve the solder ball problems. For example, when a replacement stack package 15 is attached to the module substrate 10, it may be advantageous to apply heat to only the first solder balls 16a of the lower unit package 14a. However, a specific targeted heat application may not be feasible. In practice, heat is applied to the entire replacement stack package 15. As a result, heat may be applied to the second solder balls 16b. As a result, faults 18a and 18b may occur to the second solder balls 16b as shown in
In an embodiment of the present invention, a method of bonding a ball grid array (BGA) package includes providing a lower-melting-point solder on solder balls of the BGA package, and bonding the lower-melting-point solder on the solder balls to a module substrate at a temperature between the melting point of the lower-melting-point solder and the melting point of the solder balls, wherein the lower-melting-point solder has a melting point lower than the solder balls.
In another embodiment of the present invention, a method of repairing a ball grid array (BGA) package, includes removing a defective BGA package from a module substrate, providing a lower-melting-point solder on solder balls of a replacement BGA package, and bonding the lower-melting-point solder on the solder balls to the module substrate at a temperature between the melting point of the lower-melting-point solder and the melting point of the solder balls, wherein the lower-melting-point solder has a melting-point lower than the solder balls.
The embodiments of the present invention will be better understood with reference to the following detailed description thereof provided in conjunction with the accompanying drawings.
Example embodiments of the present invention will now be described more fully hereinafter with reference to the accompanying drawings. The drawings are provided for illustrative purposes only and are not drawn to scale. The spatial relationships and relative sizing of the elements illustrated in the various embodiments may be reduced, expanded or rearranged to improve the clarity of the figures with respect to the corresponding description. The figures, therefore, should not be interpreted as accurately reflecting the relative sizing or positioning of the corresponding structural elements that could be encompassed by an actual device manufactured according to the example embodiments of the invention.
The present invention may be embodied in many different forms and should not be construed as limited to the example embodiments set forth herein. Rather, the disclosed embodiments are provided as working examples. Aspects of this invention may be employed in varied and numerous embodiments without departing from the scope of the invention.
Further, well-known structures and processes are not described or illustrated in detail to avoid obscuring the present invention. Like reference numerals are used for like and corresponding parts of the various drawings.
Referring to
For illustrative purposes, it is assumed that after an electrical test process, the BGA package 20a is determined to be faulty. The BGA package 20a may be replaced with a replacement package through a repair process. First, heat may be applied to the faulty package 20a to separate it from the module substrate 10.
Heat sinks 30 may be used to cover and protect adjacent packages 20 from the heat. The heat may be applied to the BGA package 20a using a heating apparatus 32. The heating apparatus 32 may eject nitrogen gas at about 450° C. for about 60 seconds.
The solder balls 22a of the BGA package 20a are melted by the heating apparatus 32, and the BGA package 20a is separated from the module substrate 10. The heating apparatus 32 may have a vacuum suction unit to remove the BGA package 20a by vacuum suction.
Referring to
Referring to
Formation of the lower-melting-point solder 26 may include placing a stencil 40 on the replacement solder balls 22b. The stencil 40 may have openings 40a formed corresponding to the locations of the replacement solder balls 22b. The diameter of the opening 40a is usually smaller than that of the replacement solder ball 22b so that the stencil 40 can be placed on the replacement solder balls 22b. For example, the diameter of the opening 40a may be about 0.4 mm and the diameter of the replacement solder ball 22b may be about 0.5 mm. Also, the thickness of the stencil 40 may be about 0.15 mm.
The lower-melting-point solder 26 may be provided on the stencil 40 and applied into the openings 40a with a squeeze 42. Thereby, the lower-melting-point solder 26 may be printed on the replacement solder balls 22b.
As described above, the lower-melting-point solder 26 may be formed of materials having a lower melting point than the replacement solder balls 22b. The replacement solder balls 22b and the low-melting point solder 26 may be formed from Sn/Pb, Sn/Ag/Cu, Sn/Ag, Sn/Cu, Sn/Bi, Sn/Zn/Bi, Sn/Ag/Bi, Sn/Ag/Zn, In/Sn, WAg, Sn/Pb/Ag, In/Pb, Sn, Sn/Pb/Bi, or Sn/Pb/Bi/Ag.
Although the solder materials may be the same for the replacement solder balls 22b and the lower-melting-point solder 26, they have different melting points from each other by adjusting their compositions and distribution ratio. The replacement solder balls 22b and the lower-melting-point solder 26 may be formed by suitably selecting from the solder materials. For example, the replacement solder balls 22b may be formed of Sn/Ag/Cu having a distribution ratio of 96.5/3/0.5 and a melting point of 217° C., and the lower-melting-point solder 26 may be formed of Sn/Pb having a distribution ratio of 63/37 and a melting point of 183° C. In other embodiments, the replacement solder balls 22b and/or the lower-melting-point solder 26 may be formed from Sn/Ag having a distribution ratio of 96.5/3.5 and a melting point of 221° C.; Sn/Cu having a distribution ratio of 99.3/0.7 and a melting point of 235° C.; Sn/Bi having a distribution ratio of 43/57 and a melting point of 139° C.; and, Sn/Zn/Bi having a distribution ratio of 89/3/8 and a melting point of 187° C.
Referring to
Table 1 illustrates example process conditions of the solder reflow process. Here, the solder balls 22b is formed of Sn/Ag/Cu having a distribution ratio of 96.5/3/0.5, and the lower-melting-point solder 26 is formed of Sn/Pb having a distribution ratio of 63/37.
In a solder reflow process under the process conditions of Table 1, although the peak temperature may be set between about 210° C. and 230° C., temperature applied to the solder balls 22b and the lower-melting-point solder 26 may, in practice, range between about 183-217° C., e.g., the melting point of Sn/Pb and the melting point of Sn/Ag/Cu, respectively. As a result, the replacement solder balls 22b do not melt, but the lower-melting-point solder 26 melts. Therefore, a solder reflow process may be set to a temperature between the melting point of the solder balls 22b and the melting point of the lower-melting-point solder 26.
Referring to
For illustrative purposes, it is assumed that after an electrical test process, a specific unit package has been determined to be faulty, wherein the entire stack package 50a including the faulty unit package may be replaced with a replacement stack package 50b by a repair process. First, heat may be applied to the stack package 50a to separate it from the module substrate 10. This heating may be performed in substantially the same manner as that illustrated in
Referring to
Referring to
During the solder reflow process, heat applied to the first and replacement second solder balls 52c and 52d and the lower-melting-point solder 56 may range between the melting points of the first and second replacement solder balls 52c and 52d and the melting point of the lower-melting-point solder 56. Thereby, the second replacement solder balls 52b are less susceptible to faults caused by heat used in the solder reflow process.
A soldering method in accordance with the example embodiments of the present invention may be characterized by use of a lower-melting-point solder. For example, a lower-melting-point solder may be implemented in mounting BGA packages on a module substrate. The use of lower-melting-point solder may lead to improved package repairs.
The temperature cycle (TC) test may be a reliability test for packages, which tests solder joint reliability at a variety of temperatures between −25° C. and 125° C. The temperature cycle may last about 30 minutes, and may include temperature maintenance at −25° C. for about 10 minutes, a temperature rise for about 5 minutes, a temperature maintenance at 125° C. for about 10 minutes, and a temperature decline for about 5 minutes.
The conventional BGA package using solder balls formed of Sn/Ag/Cu having a distribution ratio of 96.5/3/0.5 has a reliability of TC1000. In other words, reliability is maintained during 1000 temperature cycles. A BGA package of example embodiments of the present invention formed of Sn/Pb having a distribution ratio of 63/37 has reliability between TC1500 and TC2000. That is, reliability may be maintained between 1500 and 2000 temperature cycles.
Although non-limiting embodiments of the present invention have been described in detail hereinabove, it should be understood that many variations and/or modifications of the basic inventive concepts herein taught, which may appear to those skilled in the art, will still fall within the scope of the example embodiments of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-28594 | Apr 2005 | KR | national |
