with Reworkable Wafer-Level Underfill Ken Gilleo

with Reworkable Wafer-Level Underfill Ken Gilleo - ET-Trends David Blumel Alpha Metals Ken@ET-Trends. com KBG

Outline • The Packaging Revolution • Flip Chip vs. CSP • Why Underfill? • Classes of Underfill • Final Generation FC; a CSP • Conclusions KBG

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smaller faster cheaper KBG

Is the KEY to achieving: KBG

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The whose time already came! Sm al le r Faster = more leads “Can’t be solved by packaging evolution” KBG

n 2 > 4 n-4 KBG

1960's The Entire Packaging History Hot for the 21 st Century FC-BGA Flip Chip (C 4) Flip Chip (re-Engineered) Lead Frame Chip-on-Board BG A TCP (TAB) Feed-thru Flip Chip Strip m. BGA CSP/FC-BGA SMT Beam Lead Chip KBG micro-SMT GA TB Spider

• Perimeter Leads Area Array • Size: chip scale • Packaging: minimal • Packaging: post- and concurrent • Paths/lead length: shorter 3 2 ULTIMATE IC SMT KBG COB & TAB DCA 1

Is Flip C hip a True PA CKAGE ? KBG

th e Translation: IC to PCB Removability Environmental Protection Standardization KBG

The Original Flip Chip was a CSP IBM KBG

FLIP CHIP 360 o REVOLUTION 1963 1990’s CSP 1964 New bumps, organic substrate + Underfill High lead, ceramic substrate KBG CSP again

Flip Chip Components • Under Bump Metallization • Bumps & bumping • Joining materials & agents • Assembly processes • Underfill KBG

Bumping Methods • Attach discrete spheres; • Print joining mat's; Au, Cu, Sn/Pb or Conductive Adhesive metal vapor • Vacuum deposit metal: old, still alive • Electrolytic plating; Au, Cu, Sn/Pb, Ni (cost issue? ) • Electroless plating; Au, Cu, Ni (NEWER) • Fluid jet molten metal; • Stud bump with; • Material transfer; KBG Sn/Pb (VERY NEW) Sn/Pb, CU or Au (single chip) Sn/Pb or Cond. Adhes. ; paste or film

• Switch to organic substrate – Causes large thermal mismatch – Low reliability in thermocycle • Mismatch must be addressed – low CTE organic substrate – columns instead of bumps – non-fatiguing joints? ? ? – mechanical coupling: chip-to-substrate KBG

Thermal Mismatch Kills Reliability Heating Cooling CHIP Sn/Pb KBG

UNDERFILL Mechanism KBG in tra p o s i t i o n ns p o s i t i o n ed Y co Y

Underfill: What You • A real aggravation • Added equipment • Added floor space • Added cost • Reduced yield KBG

Underfill: What You • Self-Dispensing • Self-Fluxing • No added equipment • No added time required • Cost-effective • Reworkable KBG

Underfill Events • “Underfill Effect” discovered: 1960’s • Slow flow, slow cure the norm: early 1990’s • Fast flow (>2. 5 cm/min. ), 30 min. cure: 1995 • Pre-dispense flux-fill R&D: mid-1990’s • Snap flow (>3 cm/min) /Snap cure (5 min. ): 1997 • Convert FC to SMT: 1998 - 1999 • Wafer-level: coming in 1999 - 2000 KBG

Types of Underfill APPLIED to SUBSTRATE Chip/Wafer Chip & Substrate Concurrently KBG PHASE Pre. Dispensed Post. Dispensed Liquid Available NA Solid Available NA Liquid NA ? Solid R&D NA Liquid Available Solid NA NA

Capillary Type (post dispensed) • Flow rate is close to max. • Cure time is close to min. • Still adds – equipment – space – time – cost • Result: FC = SMT KBG

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Pre-Dispensed Liquid • Process control is critical • Requires dispenser/printer • Solder reflow oven provides cure • Enables FC = SMT • Result: next generation underfill KBG

Pre-Dispensed Flux/Underfill Not Assembled Post-Dispensed Underfill Pre-Assembled KBG

Pre-Dispense Solid on Substrate • Film-on-PCB – Special, expensive equipment – Not an SMT process – Doesn’t address underfill problems An old concept? KBG

Anisotropic Conductive Adhesive ACA film has a built-in underfill and is the 1 st example of pre-dispensed solid underfill. KBG

Pre-Dispense Solid on Chip • Wafer-level applied • Self-fluxing • Dry solid • Integral to Flip Chip • True SMT process • Transparent to assembler • Can be reworkable KBG

Liquid polymer-based composition is coated onto Flip Chips at wafer-level and then converted to a SOLID that: (1) Permits a bumped wafer to be diced into Flip Chips. (2) Provides flux for assembly. (3) Liquefies to a thermoplastic underfill during reflow. (4) Polymerizes and wets substrate during reflow step. (5) Remains reworkable after reflow stage cure. KBG

Ramifications: • FC becomes a std. SMT process. • FC becomes CSP if reworkable. • Underfill becomes a semiconductor process. • The ready-to-bond FC becomes the most costeffective minimal package. • Success can make this package the dominant micropackage. KBG

Assembly Process • Pick & Place FC from any format • Reflow • flux melts/activates • underfill liquefies/wets • solder melts/forms joint • underfill solidifies • Test • Rework if required KBG

Solder joints form, underfill properties generated T E M P KBG Melts; flux activates, begins to bond to substrate Flux has deactivated, material is now an underfill TIME in Solder Reflow Oven

Issues & Challenges • Materials; single or multiple? • Shelf life, what is required? • What wafer Coating process? • Dicing with polymer in place? • Assembly – voiding, filleting, adhesion – process sensitivity KBG

FLIP CHIP INTEGRTATED/FLUXFILL Type 1 - Single material converts from flux to underfill during reflow Solid Flux KBG

FLIP CHIP INTEGTRATED FLUX/UNDERFILL Type 2 - Two separate materials Solid Thermoplastic Underfill Solid Flux Many variations KBG

Status Technology 1 -LAYER MATERIALS complete being optimized WAFER COATING being optimized selection stage DICING Feasibility confirmed to be determined FC ASSEMBLY confirmed to be determined RELIABILITY KBG 2 -LAYER to be determined

Phase 1 Test Platform Transparent 12 mm x 12 mm Flip Chip Bonded to Copper with single-layer Flux/Underfill by running through an IR reflow oven at 220 o. C Copper sheet Purchased quartz FC with Sn/Pb bumps Flux/underfill after heating KBG Delco is not a sponsor or participant

Conclusions • Today’s underfills impede FC • FC = SMT: required for max. success • Underfill can be a semicon process • FC will become a CSP again • Result: best micropackage solution KBG

The Ultimate Micro Package Everything should be made as simple as possible but not simpler. Albert Einstein KBG Just add heat; some assembly required.

with Reworkable Wafer-Level Underfill Ken Gilleo — ET-Trends