BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an exploded perspective view of a BGA with PCB, showing stress relief pins attached to the chip substrate of the BGA, with portions of the pins shown in phantom;
FIG. 2 is an exploded perspective view of a BGA with frame, showing stress relief pins attached to the frame, with portions of the pins shown in phantom;
FIG. 3 is a perspective view of the frame engaged with the BGA of FIG. 2, with portions of the pins shown in phantom; and
FIG. 4 is a side elevation view of the PCB 14 with pin support structure (either the chip substrate of FIG. 1 or the frame of FIGS. 2 and 3), schematically showing various methods for mounting the pins to the PCB.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 illustrates a ball grid array (BGA), generally labeled 2. The BGA includes a circuit chip 4 supported on a substrate 6. Plural solder balls 8 are arranged on the underside of the substrate 6. The BGA 2 may be attached a printed circuit board 14, or PCB, by soldering the balls 8 onto the PCB 14 by means of heat. By “balls” is meant both spherical balls proper as well as cylindrical solder columns. As recognized herein, stress may build up on the soldered balls 8 between the BGA 2 and the PCB 14 and can be lessened by use of the below-described pins.
With greater specificity, pins 20 are attached to either the corners, as shown in FIG. 1, and/or to the edges of the substrate 6, which supports the circuit chip 4. The pins 20 may alternatively be attached to a preferably hollow parallelepiped-shaped frame 22 that can be glued to the substrate 6 of the BGA 2 as shown in FIG. 2. A glue is indicated at 24 in FIG. 2. The frame 22 is configured to border the substrate 6 of the BGA 2 under equal margins and can if desired slightly overlap the edges of the BGA 2, as shown in FIG. 3, with a window 24 being formed centrally in the frame in non-limiting implementations to expose the chip 4. In either the embodiment of FIG. 1 or the frame embodiment of FIGS. 2 and 3, the pins 20 are shown extending down toward the PCB 14 from the corners of the chip substrate 6/frame 22, it being understood that pins 20 can also be provided along the edges of the substrate 6/frame 22.
In any case, the pins 20 are elongated and are straight compared to the balls 8. The pins 20 can be made of solder material so that the pins 20 can be soldered to the PCB 14 in similar manner to the balls 8, thereby relieving nearby balls 8 of stress.
The BGA 2 in FIG. 1 may be considered to be a “BGA”, with the BGA 2 with frame 22 of FIGS. 2 and 3 also establishing a “BGA”.
FIG. 4 shows various ways in which the pins 20 can be engaged with the PCB 14. As the left-moist pin 20 shown in FIG. 4 illustrates, a pin 20 can extend through a respective hole 26 in the PCB and be soldered to the PCB on the surface 28 of the PCB facing away from the BGA 2 in a so-called “pin-through-hole” method.
Alternatively, as shown by the middle pin in FIG. 4, the pins 20 can be soldered to the surface 30 of the PCB 14 that faces the BGA 2 in a so-called “surface solder” method.
Yet again, as shown by the right-most pin in FIG. 4, a pin 20 can extend through a respective hole 32 in the PCB from the surface 30 of the PCB 14 to the opposite surface 28 and be engaged with a threaded fastener 34 on the opposite surface 28 of the PCB. In this latter embodiment the pin 20 may be threaded. In any case, in non-limiting implementations the fastener 34 can be tightened as desired to pre-load the assembly to minimize the typically residual BGA package strain (which can range from two hundred micro-strains to six hundred micro-strains). Moreover, the fastener 34 at one corner of the package might be tightened to a different torque than that used to tighten the fastener at another corner as necessary to alleviate stress from warpage.
Only one of the three methods shown in FIG. 4 for engaging the pins 20 with the PCB 14 may be used in any given package, or any two or even all three may be used in a single package.
While the particular SYSTEM AND METHOD FOR REDUCING STRESS-RELATED DAMAGE TO BALL GRID ARRAY ASSEMBLY is herein shown and described in detail, it is to be understood that the subject matter which is encompassed by the present invention is limited only by the claims.
Patent Application
20080042270
