The present invention relates generally to device packages, and more particularly to a substrate-based chip package.
Substrate-based chip packages are also referred to for example as BGA packages, BGA standing for Ball Grid Array. U.S. Pat. No. 6,048,755, which is incorporated herein by reference, teaches a method for producing a BGA package using a substrate with a patterned solder resist mask.
In the case of such substrate-based chip packages, it is very important that care is taken to protect all the edges of the chip, since cracks or other mechanical damage can also have effects on the active chip side. Such damage may arise in the course of handling, during the back-end process or else with the customer. In order to avoid this, a molded cap (covering material or molding compound), which envelops the rear side of the chip and adjacent regions of the substrate, may be used.
For durable functioning of the chip package, it is of special significance that the covering materials have very good adhesive properties with respect to the surfaces of the different materials of the package. A particular weak point in the package in this case is the solder resist, which for reasons of minimizing warpage is applied on both sides. That is to say, it is also applied on the chip side. Warpage is to be understood as meaning that in a layered structure a distortion of the substrate occurs under the influence of temperature unless layers of different coefficients of expansion are present on both sides, or at least are irregularly distributed.
The solder resist not only absorbs a relatively large amount of moisture (up to about 8%), which is unfavorable for the reliability characteristics of the package, but also significantly reduces the adhesion of the die-attach material and of the molding compound on the substrate base material. In addition, it is also very difficult to harmonize the adhesive properties of the molding-compound and die-attach materials (adhesive) over the entire temperature range (−65° C. to 150° C. in the extreme case). A so-called CTE (coefficient of thermal expansion) mismatch arises, as a result of which the reliability characteristics are significantly reduced.
Furthermore, the moisture content of the solder resist can lead to problems of reliability as a consequence of the higher soldering temperatures due to the use of lead-free solder materials.
The consequence is that the packages may already delaminate, that is come apart, at the molding compound/solder resist, solder resist/substrate and solder resist/die-attach material interfaces during preconditioning.
In order to achieve an improvement in this, the chip is either molded around completely (TSOP), provided with molded caps (for example, BOC with backside protection or BSP) or with other mechanical coverings on the module level. In the case of U.S. Pat. No. 6,048,755, it was attempted to solve the problem at least partly by removing the solder resist under the chip.
In the case of the molded cap, it was attempted to solve the problem by optimizing the adhesive force on the solder resist, which however did not lead to optimum reliability characteristics.
The preferred embodiment of the invention relates to a substrate-based chip package that includes a substrate on which a chip is fastened by a die-attach material. The substrate is provided with a solder resist (e.g., on both sides) and, on the side that is opposite from the chip, has conductor tracks which are provided with solder balls and are connected to the chip by means of wire bridges. The wire bridges extend through a bonding channel, which is sealed with a glob top. The chip and the substrate on the chip side are encapsulated by a molded cap.
In one aspect, the invention therefore provides a substrate-based chip package of the type stated at the beginning with which the problems mentioned no longer occur and which can be realized at a low cost. In the preferred embodiments, the invention provides a substrate-based chip package where the solder resist on the chip side is cut out at least partially, so that an interface with greater adhesive properties is created at least for the molding compound on the substrate.
A reduction in the moisture absorption and an improvement in the adhesive strength and bending of the molded cap on the substrate is achieved by the invention.
In a variant of the invention, solder resist is arranged between the die-attach material and the substrate, the region under the molding compound being free of-solder resist.
A further refinement of the invention is characterized in that the die-attach material rests directly on the substrate with a greater area extent than the chip and in that the molding compound rests on the solder resist and partly on the die-attach material.
In a special refinement of the invention, the solder resist on the chip side is arranged parallel to two outer edges of the substrate. In this manner, a reduction in the thermally induced bending of the substrate is achieved.
It is particularly advantageous if, in the case of rectangular substrates, the solder resist on the chip side is arranged parallel to the two longer outer edges of the substrate. In this way, a significant reduction in the bending of the substrate is achieved.
The invention is to be explained in more detail below on the basis of an exemplary embodiment. In the associated drawings:
The making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.
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In order to achieve special warpage behavior, however, the solder resist 4 may also be arranged on the chip side of the substrate in such a way that only two strips of solder resist 4 are obtained.
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Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
Number | Date | Country | Kind |
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103 25 029 | Jun 2003 | DE | national |
Number | Name | Date | Kind |
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6048755 | Jiang et al. | Apr 2000 | A |
6667560 | Goh | Dec 2003 | B2 |
6724076 | Kahlisch et al. | Apr 2004 | B1 |
20020030266 | Murata | Mar 2002 | A1 |
Number | Date | Country |
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199 54 888 | May 2001 | DE |
0 810 655 | Dec 1997 | EP |
Number | Date | Country | |
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20050006741 A1 | Jan 2005 | US |