1. Field of the Invention
The present invention relates to an improved singulation saw that is adaptable to be used as a dicing or wafer saw. More particularly, the present invention relates to a novel substrate saw having a plurality of rotating saw blades adapted to cut or saw substrates in two opposite directions of relative movement.
2. Description of the Prior Art
Dicing saws and singulation saws are known. Dicing saws fitted with special saw blades have been used to singulate or separate semiconductor die from a semiconductor wafer mounted on a layer of adhesive on a stretchable plastic film. The dicing saw is preferably programmed to cut streets between rows and columns of die to a depth that penetrates through the wafer into the adhesive layer, thus, completely saw-cutting one die from others. Most prior art saws are designed to saw a single street or cut across a wafer then raise the saw blade and return to the same side and start the next cut.
Advance Packaging (AP) devices include a die and a carrier. The sawn die are mounted onto a carrier such as a substrate or printed circuit (PC board) that is provided with conductive leads and/or conductive balls and/or pins. AP technology includes Ball Grid Array (BGA); Micro BGA (μBGA); Flip-Chip devices; Chip Scale Packaging, etc. All such devices are preferably mounted on the substrate with other AP die devices and need to be singulated one from another.
Quite often the AP devices are separated from each other by wide streets which cannot be cut and removed by wide saw blades. This requires two saw cuts to remove material forming the street that separate the devices. This dual cut street also causes wafer parts and street scrap to fall away or to be projected by the moving saw blade into fragile parts of the dicing saw such as resilient bellows found in dicing saws. A further problem is that the dicing saw must be shut down to remove the scrap that accumulates. Thus, prior art slurry drain systems are not designed to pass substrate scraps and the conversion of dicing saw systems for use in singulating substrates require a complete shut-down and clean-up periodically. Large pieces of stripped substrate cannot be flushed by liquid means as possible when only wafer slurry is present.
Some AP devices are separately encapsulated on a substrate apart from other devices, however, some manufacturers gang encapsulate all AP devices on the substrate with a uniform layer of encapsulating resin such as epoxy which shrinks when passing into the cured state. The gang encapsulated process causes bowing or distortion of the substrate strip and presents problems for the singulation saws when separating one device from another.
Prior art dicing saws have been provided with wafer handlers. When the wafer handler is coupled to one side of the saw it inputs a wafer to be cut and subsequently removes a wafer after it is cut. Such handlers are sometimes called in-and-out handlers. The disadvantage of the in-and-out handler is that no productive sawing can be accomplished during the unloading and reloading of the wafers. When dicing saws are adapted to singulate encapsulated AP devices the same non-productive time occurs for unloading and loading strips or substrates with plural AP devices embedded thereon.
It has been suggested that prior art dicing saws be modified so that the input handler could supply a wafer to be cut at one side of the saw and the output handler could receive a wafer after being cut. No such saw is known to exist because this would require two handlers that take up twice the handler floor space as well as a major redesign of the transport system in the saw itself.
Prior art dicing saws have been provided with two or more saw blades mounted on a single spindle for simultaneously cutting plural paths in a wafer or substrate. This results in a decreased time for cutting a complete wafer. It is not possible to use such systems where very high precision is needed or the street between the devices requires two cuts to remove street material. Further, only when the die being cut is perfectly square and the saw blade is the same width as the street is a multi-blade on one spindle system of practical use.
It would be desirable to provide a new design singulation saw that recognizes and solves all of the above-mentioned problems found in modification or conversion of dicing saws to perform singulation of AP devices. It would be desirable to provide a singulation saw that may be modified or converted for use as a dicing saw while retaining all of the improvements that result in increasing through-put.