A study on fine pitch Au and Cu WB integrity vs. Ni thickness of Ni/Pd/Au bond pad on C90 low k wafer technology for high temperature automotive

Leng, Eu Poh; Song, Poh Zi; Kheng, Au Yin; Yong, Cheng; Tu, Anh Tran; Arthur, John; Downey, Harold; Mathew, Varughese; Yin, Chee Yit

doi:10.1109/iemt.2010.5746744

Cited by 3 publications

(4 citation statements)

References 3 publications

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“…With the defined window, XoAA device passed XoAA assessment and subsequently meet reliability requirement. Thus, it proven that this methodology is workable.In summary, Copper wire bonding on NiP based bond pad (plated on top of Al) is feasible and inline with published papers [1,2]. However, pad bending need to be considered to avoid cratering on XOAA device.…”

supporting

confidence: 55%

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Pad bending improvement on copper wire bonding on NiP/Pd/Au bond pad

Heong¹,

Kim

Yong³

2012

2012 35th IEEE/CPMT International Electronics Manufacturing Technology Conference (IEMT)

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Due to the high gold price, conversion from gold wire to copper wire has been a widely accepted method in semiconductor assembly for cost reduction. However, conversion from gold wire to copper wire is not a straight forward conversion. Copper wire is about 30% harder than gold wire and the commonly used bond pad metallization is Aluminium base (which is softer compare with Copper). Potential challenges include pad cratering, Al splash, lifted ball and reliability concern. Therefore, harder bond pad (plated on top of Aluminium) with Nickel as the base material was introduced. Ni which is harder than Cu, offer protection to the underlying structure, especially for probe and bond over active area products (XoAA).Technically, NiP will only bend down when the bonding impact is applied. The underneath Aluminium layer will be squashed out exhibited bond pad bending. Bond pads bend down at the centre coincide with the ball bond position and bend upward at both edges of bond pad. More severe pad bending will be observed at the direction parallel to the direction of ultra-sonic vibration and potentially cause oxide crack underneath the bond pad. Thus, the understanding of interaction between wire bond parameters and bond pad bending is very crucial to prevent oxide crack. This paper presents pad bending improvement study focusing on NiP thickness, bonding parameters and capillary design.In the stage of screening to identify the key input parameters, the results show very significant reduction on pad bending by lowering ultrasonic power. However, there is a limit for ultrasonic power in order not to compromise on the wire bond performance on non stick on pad occurrence. Thus, there is a need to consider capillary with build in design that can function with lower ultrasonic level. From experiment run, it is proven that capillary design can greatly reduce the ultrasonic power required (more than 50%) without occurrence of non stick on pad. Besides this, Ni plating thickness also shows significant impact on pad bending, a DOE approach was used to characterize and define suitable bond parameters window. A three factors (Ni plating thickness, ultrasonic power and bond force), two level factorial design was used to examine interaction and main effect. The experiment shows significant main effect by Ni plating thickness and ultrasonic power. Pad bending is less severe for lower ultrasonic power and thicker Ni plating thickness. With the defined window, XoAA device passed XoAA assessment and subsequently meet reliability requirement. Thus, it proven that this methodology is workable.In summary, Copper wire bonding on NiP based bond pad (plated on top of Al) is feasible and inline with published papers [1,2]. However, pad bending need to be considered to avoid cratering on XOAA device. Pad bending can be improved with lower ultrasonic power, capillary design and thicker Ni plating thickness. NiP plating thickness should also be included in the DOE to define suitable parameter window.

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supporting

confidence: 55%

“…In summary, Copper wire bonding on NiP based bond pad (plated on top of Al) is feasible and inline with published papers [1,2]. However, pad bending need to be considered to avoid cratering on XOAA device.…”

supporting

confidence: 55%

Pad bending improvement on copper wire bonding on NiP/Pd/Au bond pad

Heong¹,

Kim

Yong³

2012

2012 35th IEEE/CPMT International Electronics Manufacturing Technology Conference (IEMT)

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“…A copper wire bond on more robust bond pad metallurgy would be another alternative. The strong wire bond pad metallurgy, NiPd has been discussed in some studies [3][4][5]. The Al splash issue was solved by using harder NiPd bond pad surfaces.…”

Section: Introductionmentioning

confidence: 99%

“…Thin Ni layers can be deformed by the bonding force during copper wire bondin thin Ni of 1µm is used. [5] In this paper, the study was carried out o with 2.5µm thick Ni. A small copper bal aimed to understand the stress effect of sm the Cu/low-k chip with Al bond pad and A The study on the response of the bond pad pad or Cu/low-k damage with increa parameters was carried out.…”

Section: Introductionmentioning

confidence: 99%

Fine pitch copper wire bonding on 45nm tech Cu/low-k chip with different bond pad metallurgy

Wai

Jaafar

Chew

et al. 2011

2011 IEEE 13th Electronics Packaging Technology Conference

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Wire bonding technology has been widely used in the semiconductor industry for interconnection between device and substrate. Gold wire has been used in industry for many years; however with the increase in the price of gold in the past few years, copper wire has become an alternative. Copper wires have better electrical and thermal performance than gold wire. However due to coppers hardness, the bonding of copper wire to the soft Al bond pad becomes a challenge especially for devices with sensitive and fragile structures underneath the Al bond pad. An optimized Al remnant is required for achieving good reliability [1-2]. A robust bond pad structure with different bond pad material could reduce the impact to structures under the bond pad, minimize Al splash and remove the concern associated with Al remnant for reliability. In this study, copper wire bonding on bond pads with different hardness will be evaluated; they are Al pad and NiPd on top of Al pad. An ASM Eagle Xtreme bonder was used for the study. The forming gas (95%N 2 5%H 2 ) flow rate of 0.4/0.8ℓ per minutes was controlled by a digital flow meter which provides a consistent supply of forming gas. Forming gas maintain an inert environment during the electrode flame-off for free air ball. Capillary with a hole size of 21.6µm, chamfer diameter of 28µm and face angle of 11 o was designed for fine pitch bonding with matte surface to enhance the gripping of ball and wire during bonding. A 4N copper with 0.7mil in diameter was used to evaluate the bonding on a Cu/low-k chip with two different bond pad metals with thicknesses of 2.1µm for the Al bond pad and 1.4µm Al/2.5µmNi/0.3µmPd bond pad finish. The NiPd layer used in this study was actually two separate layers which consist of 2.5µm of Ni and 0.3µmPd. Optimized bonding parameters were used on different surfaces to compare the results of bond quality. Comparisons of the deformation of the Al layer and NiPd layer as a result of the bonding was studied. NiPd is harder and could act as a barrier to prevent the direct interaction of the copper wire on the Al bond pad and thus prevent the problems of Al splash especially in fine pitch wire bonding. In this study, target ball size of 34µm were bonded to 55µm bond pad pitch Cu/low-k chips. The effects of the NiPd layer on various parameters were compared with Al bond pad. Evaluated sample were subjected to thermal aging to further understand the effects of temperature on bond quality. (Key words: Cu/low-k, Al bond pad, NiPd bond pad, Copper wire)

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