What is DST? (back to top)

Direct Stacking Technology is an innovative memory stacking solution that simplify both the stacking design and the manufacturing process. Previous memory stacking techniques involve the use of additional materials such as a lead frame or PCBs. However, Direct Stacking Technology requires no supporting materials. This translates into a staking design that requires far fewer solder joints. Compared to the "Indirect stacking" , Direct Stacking Technology requires about 1,200 fewer solder joint and this substantial reduction in the number of solder joints required per stack enables Direct Stacking Technology to achieve reduced manufacturing time, higher yield, greater reliability, and reduced cost per manufactured item. The following table shows the side by side comparison between Direct Stacking Technology from POLYSTAK and "Indirect Stacking Technology" from competitor's.

DST vs IST
Characteristic	DST(Direct Stacking)	IST (Indirect Stacking)
Yield	99% guaranteed	?
Added Materials	None	Copper alloy layer
Visual Inspection	Excellent	Okay, but metal leads block the sight in certain angle
Solderability	Better than a single TSOP (leads have a very thin coat of solder after the assembly process)	Almost the same as a single TSOP
Number of Solder Joints Per Lead Per Stack 18 Stacks on Module	1* 66* 2,376 *	2 132 3,564
Module Reparability Using Stacked Parts	Easy (Same repair equipment and techniques as used for single TSOPs)	Difficult
Crosstalk	Same as a single TSOP	Almost the same as a single TSOP
Frequency Response	Same as original single TSOP	Less than original single TSOP (reduced by copper alloy lead parasitics)
Changes in Mechanical Dimension after Stacking	Almost None	Metal layer cause an increment in height
Cross Sectional View

 

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