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Apr 2nd, 2014
STATSChipPAC (SCP) FlexLine : A Closer Look
At the recent IMAPS Device Packaging Conference in AZ, SCP announced FlexLineTM as a “breakthrough manufacturing method for Wafer level packaging”. iMicronews felt this attempt to leverage their e-WLB fan out technology to fan-in WLCSP was worth…A Closer Look.
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SCP notes that demand for WLCSP for advanced mobile products such as smart phones and tablets is driving capacity constraints in the industry. In support of this statement, at the Qualcomm keynote talk Steve Bezuk commented that 5 years ago very few of the mobile phone packages were WLP but now this category accounted for near 50% of the packaged ICs.

SCPs Tom Strothmann, points out that OSATS have traditionally been forced to use wafer processing equipment sets for both 200 and 300mm wafers that typically have higher cost and capability than needed. 

While separate equipment sets are required to manufacture WLCSP from 200, 300 and in the future maybe 450mm wafers, SCP processes are in place for e-WLB FO-WLP which uses the same equipment set no matter what format the chips are delivered in.  

Currently, separate equipment sets are required for WLCSP from 200 or 300mm wafers whereas FO-WLP can be manufactured on the same equipment set

The SCP FlexLine process flow is based on the SCP commercial eWLB FO-WLP process. Fan-out package solutions have been in HVM since 2009 with single die and multi-die products with more than 500MM units shipped. eWLB has passed all standard component and board level reliability tests.

The process dices and reconstitutes incoming wafers at the start of the process to an optimized panel size, which, according to SCP results in the following advantages:
• FlexLineTM provides a simplified supply chain
• One qualified manufacturing source can provide FIWLP, FOWLP, 2.5D eWLB, and 3D eWLB using the same: equipment, device structures, material sets & location
• Simplified bill of materials (BOM)
• Product with low fab yield can enjoy reduced packaging cost by packaging KGD only
• Enables advanced node production with multi-level RDL for WLCSP
• Maximizes flexibility with current equipment set
• Wafer level packaging equipment becomes independent of incoming silicon size
                 − Fan-in: 100mm - 450mm (with or without sidewall)
                 − Fan-out : 100mm - 450mm
• A change in loading between wafer diameters or package types does not adversely impact utilization
                 – Full utilization ensures lowest cost
• Solves the dilemma of 450mm die for WLCSP without expensive 450mm IC Equipment

FlexLine will reportedly manufacture a variety of package types from a variety of wafer sizes

2.5/3D products that can be built in a Single FlexLine Manufacturing Line include:

2.5/3D Packages which can be manufactured on the FlexLine

To create a standard WLCSP SCP offers the following process flow:
• Dice the wafer to dimensions slightly larger than nominal die size
• Process through reconstitution, redistribution and ball drop
• singulate removing the mold compound from the side of the die and reducing the die size back to the nominal size

To create an encapsulated WLCSP (eWLCSP):
• Dice the wafer at nominal die size
• Process through reconstitution, redistribution and ball drop
• Final singulation is done larger than the die size, leaving a protective layer of mold compound on the sides of the die
• The end product here  is a eWLCSP that cannot be made with conventional WLCSP processes

SCP is not disclosing specifics regarding EMC and RDL polymers at this time as this is specific to their customers’ requirements.

WLCSP from the FlexLine

In terms of economics, SCP proposes that the added cost of reconstitution is offset by the larger panel size that is processed. So obviously cost reduction becomes more compelling as panel size is increased.

Strothman indicates that “by normalizing multiple wafer diameters to a uniform processing size using  reconstitution technology, a large percentage of WLCSP designs  and flip chip designs that have been converted  are already more cost effective. That percentage will expand rapidly as the panel size used in the FlexLine process increases. The FlexlineTM solution for WLCSP is very viable today for incoming wafer sizes of 200mm and below, and there are already situations where this approach offers significant benefits for 300mm.  As the FlexLine panel size continues to increase, it will effectively lower the overhead processing cost per unit.” 
SCP reports that the equipment needed to enable this line “.. has been used for our Fan-out wafer level manufacturing processes” so IFTLE guesses that the current Flexline is no more than 300mm.

BJ Han, SCP executive VP and CTO commented “ ..with FlexLine we are able to help our customers achieve at least a 15-30% cost reduction using the optimum design requirements for their WLCSP devices”.

The FlexLine™ is located in their Singapore facility, with products under qualification and HVM expected in the second half of the year. Capacity of the line has not been released.



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