UBM (Under Bump Metallurgy) Systems

封装结构中的UBM介绍

UBM (Under Bump Metallurgy) Systems1. Definition of UBM 2. Role of UBM 3. UBM types and characterization 4. Case Study 5. Summary

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封装结构中的UBM介绍

Why UBM Study is required?

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封装结构中的UBM介绍

UBM Evolution

Materials Deposition

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封装结构中的UBM介绍

UBM Metals

Layer FunctionAdhesion, Diffusion Barrier Solder Wetting Oxidation Protection

Metal

Cr , Ti, Ti-W, ZnCu, Ni, Ni-V

Au, Pd

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封装结构中的UBM介绍

C-4 UBM StructureAu

Cu

Cr

C-4: controlled collapse chip connection

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封装结构中的UBM介绍

C4 Technology C4 means “ControlledCollapsed Chip Carrier” Flip Chip was developed by IBM in 1963. Flip Chip replaces the wires and leads of conventional packages with mounds of solder. C4 was based on shadow-mask evaporation of solder.

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Source : IBM Page 2002 6

封装结构中的UBM介绍

UBM Metallurgy SetsAu Cu Cr

Original C-4 Alternatives- A (Copper-Wetting)

Cr / Cu / Au

Ti / Cu / Au Ti / CuTi / Ni / Pd Ti/ Ni Zn / Ni / Au Al / Ni-V / Cu

Alternatives- B (Nickel-Wetting)

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封装结构中的UBM介绍

UBM Metallurgy SetsUBM Method Adhesion Layer Solder Diffusion Barrier Solder Wettable Layer Cr/Cr:Cu/Cu/(Au) Evaporated Cr Cr : Cu Cu TiW/Cu/(Au)/ Cu mini-bump Sputter+ Electroplating 1) Ti : W 2) Cr : Cu Cu stud/minibump Cu Al/NiV/Cu sputter Al Ni Cu ENIG Ni/Au Electroless Plating Ni Ni Au

Oxidation PreventionSuitability for 63Sn-37Pb Use with Probed Wafers Company

AuNo No Mass production in IBM & Motorola

AuPoor No AT&T, Casio, Citizen, Motorola, Aptos

CuYes Yes Delco, FCT, Lucent,

AuYes Mixed PacTech IC Interconnect

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ENIG: Electroless Nickel / Immersion Gold

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封装结构中的UBM介绍

<Cr/Cr:Cu/Cu/Au> Phased Cr:Cu layer is an extremely reliable solder diffusion barrier for high lead solders but is not suitable for eutectic Pb-Sn solders. Cr/Cr:Cu/Cu structure is a higher stress thin film than other UBMs. Therefore it is not recommended to use this UBM on probed wafers. UBM adheres well to the IC metallization and passivation, protecting the underlying bond pad. Field-proven reliability

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封装结构中的UBM介绍

Cr/CrCu/Cu(1500Å/ 3000 Å/ 8000 Å)

SnPb

SnAg

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封装结构中的UBM介绍

IMC Spalling –Cr/CrCu/Cu

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封装结构中的UBM介绍

研究了不同回流次数下SnAg/Cu的界面反应和孔洞形成机理,及 其对凸点连接可靠性的影响.回流过程中SnAg与Cu之间 Cu6Sn5相的生长与奥氏熟化过程相似.SnAg/Cu6Sn5界面中孔 洞形成的主要原因是相转变过程中发生的体积缩减.凸点的剪切 强度随着回流次数的增多而增大,且多次回流后SnAg/Cu界面仍 然结合牢固.Cu6Sn5/Cu平直界面中形成的孔洞对凸点的长期可 靠性构成威胁.

Cu3Sn相产生体积变化，对可靠性有较大影响。

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封装结构中的UBM介绍

<TiW/Cu/Au/Cu mini-bump> sputtering of TiW/Cu/Au plus electroplating of Cu mini-bump(5~25 ). UBM adheres to the wafer passivation as well as to the bond pad. Ti:W is a comparatively high stress thin film which can reduce reliability. The mini-bump generates a large amount of stress to wafer. Silicon Cratering : Variations of the Cr/Cr:Cu/Cu UBM systems (IBM/Unitive) have shown poor results with eutectic solder. This UBM is compatible with eutectic Pb-Sn solder. However, excessive brittle intermetallic layer formation can cause reliability problemIME Confidential & Proprietary Page 13

封装结构中的UBM介绍

TiW/Cu/electroplated Cu(2000Å/ 3000 Å/ 5 µm)

SnPb

SnAg

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封装结构中的UBM介绍

可控的冷却速率可控制液态温度以上时间，快速冷却可以细 化晶粒，提高强度，防止偏析，增强可靠性，避免Ag3Sn 和Cu6Sn5等树枝状结晶的形成

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封装结构中的UBM介绍

<Al/NiV/Cu> Field-proven UBM. Can withstand over 10 reflow cycles. Can be used on probed wafers without fear of affecting reliability. Al forms a strong adhesion to the wafer passivation as well as to the Al bonding pads Ni layer serves two functions : it is an excellent solder diffusion barrier, especially for 63Sn/Pb solders and it provides a solder wettable surface after Cu is consumed. Cu is used to keep the Ni from oxidizing and, unlike the plated mini-bump process, is not needed to allow the solder bump to adhere to the UBM.IME Confidential & Proprietary Page 16

封装结构中的UBM介绍

NiV/Cu(2000Å/ 8000 Å)

SnPb

SnAg

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封装结构中的UBM介绍

No IMC SpallingNiV layer still remained after heat-treatment.

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封装结构中的UBM介绍

Sn/3.5 Ag, 60µm Size Bump Fracture Analysis with UBMs

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