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== Description ==
[[Image:BGA RAM.jpg|thumb|300px|BGA [[Integrated circuit|ICs]] assembled on a [[Random access memory|RAM]] stick]]
The BGA is descended from the [[pin grid array]] (PGA), which is a package with one face covered (or partly covered) with pins in a [[grid pattern]] which, in operation, conduct electrical signals between the integrated circuit and the [[printed circuit board]] (PCB) on which it is placed. In a BGA the pins are replaced by pads on the bottom of the package, each initially with a tiny [[solder ball]] stuck to it. These solder spheres can be placed manually or by automated equipment, and are held in place with a tacky flux.<ref name=indiumcorporation>[http://www.indium.com/_dynamo/download.php?docid=323 Soldering 101 - A Basic Overview]</ref> The [[SMT placement equipment|device is placed]] on a PCB with copper pads in a pattern that matches the solder balls. The assembly is then heated, either in a [[reflow oven]] or by an [[infrared heater]], melting the balls. [[Surface tension]] causes the molten solder to hold the package in alignment with the circuit board, at the correct separation distance, while the solder cools and solidifies, forming soldered connections between the device and the PCB.They are put in water to help remove any residue after soldering.
In more advanced technologies, solder balls may be used on both the PCB and the package. Also, in stacked [[multi-chip module]]s, solder balls are used to connect two packages.
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