A ball grid array (“BGA”) package is a type of chip package wherein solder balls are used to electrically connect the BGA package to a structure external to the package, such as a printed circuit board (“PCB”). The solder balls conduct electrical signals between a chip inside the package and the external structure. A BGA package is electrically coupled to a PCB using the solder balls during a solder reflow process. During a solder reflow process, the solder balls are heated such that the solder balls melt (i.e., “reflow”) and form electrical connections (i.e., metallic bonding) with the PCB.
Many BGA packages have heatsinks coupled to a surface of the BGA package opposite the solder balls.
The stress resulting from the weight and compressive force from the heatsink 102 also may cause the solder balls 106 to be compressed in between the BGA package 100 and the PCB 104 to a degree greater than in a typical solder reflow process. This compression causes each solder ball 106 to creep and progressively expand toward adjacent solder balls 106, as shown in
One possible solution to such a problem is to apply a polymer underfill between the substrate 20 and the PCB 104. However, applying an underfill prevents the package 100 from being removed from the PCB 104. For example, if the package 100 does not function properly, the package 100 cannot be removed from the PCB 104 and replaced with a properly functioning package. Leaving an improperly-functioning package 100 on the PCB 104 substantially increases cost, particularly in applications such as servers and telecommunications.
The problems noted above are solved in large part by a solder joint support film for BGA packages under heatsink compression. One exemplary embodiment may be a system comprising a ball grid array (“BGA”) substrate adapted to electrically couple to an application board using a plurality of solder balls, and a film adapted to abut the application board and the BGA substrate, said film comprising a plurality of perforations, the solder balls adapted to couple to the application board through said perforations.
For a detailed description of exemplary embodiments of the invention, reference will now be made to the accompanying drawings in which:
a-2c show the progressive compression creeping of solder balls as the substrate is pushed closer to the PCB due to the compressive load from the heatsink;
a shows the thin film abutting the substrate, in accordance with embodiments of the invention;
b shows a PCB abutting the substrate and thin film configuration of
c shows the thin film between the substrate and the PCB, in accordance with embodiments of the invention; and
Certain terms are used throughout the following description and claims to refer to particular system components. As one skilled in the art will appreciate, companies may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections.
The following discussion is directed to various embodiments of the invention. Although one or more of these embodiments may be preferred, the embodiments disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure, including the claims. In addition, one skilled in the art will understand that the following description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to intimate that the scope of the disclosure, including the claims, is limited to that embodiment.
Presented herein is a device that supports BGA package solder joints and prevents solder ball short circuiting. Specifically, a perforated thin film is deposited between a BGA package and a PCB to provide mechanical support to the solder joints and the BGA package during a solder reflow process. The perforated thin film also prevents the solder balls from coming into electrical contact with each other due to stress applied by a heatsink abutting the BGA package.
b shows the configuration of
c shows a detailed view of the BGA substrate 20 coupled to the PCB 104 by way of the solder balls 106, and the thin film 300 situated therebetween. The stress applied to the BGA substrate 20 and the solder balls 106 by the heatsink 102 causes the solder balls 106 to be compressed, as described above. This compression causes the solder balls 106 to horizontally expand toward adjacent solder balls 106. However, because the thin film 300 is situated between some or all pairs of solder balls 106, the solder balls 106 do not expand to the degree that the solder balls 106 would expand in the absence of the thin film 300. Furthermore, for the same reason, the likelihood of two solder balls 106 causing a short circuit by coming into electrical contact with each other is considerably low or virtually nonexistent. Also, unlike underfill material, because the thin film 300 is not permanently fixed between the substrate 20 and the PCB 104, the thin film 300 may allow for replacement of an improperly-functioning package 100. Enabling such package replacements may substantially reduce costs compared to those incurred by using an underfill material between the substrate 20 and the PCB 104.
The thin film 300 may be fabricated using any suitable process such as that shown in
The above discussion is meant to be illustrative of the principles and various embodiments of the present invention. Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.