Effect of Pb free Alloy Composition on Drop/Impact Reliability of 0.4, 0.5 &amp; 0.8mm Pitch Chip Scale Packages with NiAu Pad Finish

Syed, Ahmer; Kim, Tae‐Seong; Cha, SeWoong; Scanlon, Joseph C.; Ryu, Changgyun

doi:10.1109/ectc.2007.373911

Cited by 25 publications

(15 citation statements)

References 4 publications

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“…There are many publications reporting that SnAgCu solder joints with low Ag content performed better in drop test of μBGA [3][4][5][6][7][8][9][10][11][12]. In contrast, the performance of SnAgCu solder joints in thermal cycling improved as the Ag content increases [10,[13][14][15][16][17][18][19].…”

Section: Introductionmentioning

confidence: 94%

Thermal cycling reliability of SnAgCu solder joints in WLCSP

Zeng

Nangia

2014

2014 IEEE 16th Electronics Packaging Technology Conference (EPTC)

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It has been widely reported in the literature that for packages that are required to pass thermal cycling test, the SnAgCu solder joints should have high Ag content. In this study, thermal cycling performance of a wafer level chip-scale package was evaluated with different combinations of high Ag solder (Sn3.9Ag0.6Cu) and low Ag solder (Sn1.2Ag0.5Cu) with thick and thin PCB. It was found that with the low Ag solder ball the package mounted on a thin PCB had better performance. Metallurgical analysis of solder joints, mechanical modeling of the package mounted on boards, and coplanarity measurement of the printed circuit boards were performed to understand the results. Because of the CTE mismatch between PCB and die, PCB warpage resulted in high tensile stress in solder joints in the central area, causing cracking of re-distribution layer Cu. The softer solder alloy Sn1.2Ag0.5Cu helped reduce the stress, leading to better performance in thermal cycling test. IntroductionWafer level chip-scale package (WLCSP) brings benefit to the miniaturization of devices and low cost. Compared to μBGA, the printed circuitry board (PCB) assembly with WLCSP has simpler structure and but greater stress in solder joints. See Fig. 1. In μBGA, Si die is glued on a polymer substrate and wire bonded to the pads on the substrate. Solder balls are between two polymer materials. Since the die is attached on polymer substrate by adhesive, the stress due to mismatch of coefficien of thermal expansion (CTE) between die and polymer substrate can be largely released by the glue and wires. However, for WLCSP, solder balls are placed on die. It is flip chip assembled directly on the PCB. The CTE mismatch between Si die and PCB is much larger than between substrate and PCB in the case of μBGA. The solder balls between die and PCB are under higher stress than the ones between μBGA substrate and PCB. The CTE of RF-4 PCB is about 16 ppm/°C [1], but it is only 2.5 ppm/°C for die [2]. Because of this, underfill encapsulate is recommended for WLCSP to get better package reliability. However, because of

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Section: Introductionmentioning

confidence: 94%

Thermal cycling reliability of SnAgCu solder joints in WLCSP

Zeng

Nangia

2014

2014 IEEE 16th Electronics Packaging Technology Conference (EPTC)

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“…The brittle fracture of solder joints during drop impact test is often caused by the weak interface owing to the formation of voids along IMC layers [23]. To improve the drop impact resistance of Pb-free solder joints, two approaches have been taken; reducing Ag or Cu content in SAC solder to increase the ductility of the solder matrix [89][90][91], and/or adding minor alloying elements to suppress the interfacial void formation and IMC growth [52,58,62,78,89,90].…”

Section: Drop Impact Resistancementioning

confidence: 99%

‘Effects of Minor Alloying Additions on the Properties and Reliability of Pb‐Free Solders and Joints’

Kang¹

2012

Lead‐Free Solders: Materials Reliability for Electronics

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Since July, 2006, following the EUs RoHS legislation, the consumer electronics industry has been offering 'green' products by eliminating Pb-containing solders and other toxic materials. This transition has been relatively smooth, because the reliability requirements are less stringent. However, the Pb-free transition for high-performance electronic systems (such as servers and telecommunication) is still on-going due to their rigorous reliability requirements. For example, the research and development efforts to implement Pb-free flipchip interconnections for high-end applications are still very active.In this chapter, the recent progress in Pb-free solder development, especially minor alloy additions to Sn-rich solders is reviewed in light of improving various physical, mechanical, metallurgical or electrical properties of solder joints. The topics to be discussed include those such as control of undercooling, microstructure, interfacial reactions, or void formation, as well as enhancing impact resistance, electromigration, and other mechanical properties.

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“…al. [7]. Since SnAgCu (SAC) solder alloy performs poorly compared with SnPb solder under drop test, several studies have been done to improve the reliability of lead-free solder joints by adding micro-alloying additions [8,9] or lowering Ag content [10].…”

Section: Introductionmentioning

confidence: 99%

Drop test reliability of lead-free chip scale packages

Farris

Pan

Liddicoat

et al. 2008

2008 58th Electronic Components and Technology Conference

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This paper presents the drop test reliability of 0.5mm pitch lead-free chip scale packages (CSPs). Fifteen 0.5mm pitch CSPs were assembled on a standard JEDEC drop reliability test board with Sn3.0Ag0.5Cu lead-free solder. Eight boards were edge-bonded with a UV-cured acrylic; eight boards were edgebonded with a thermal-cured epoxy; and twelve boards were assembled without edge bonding. Half of the edge-bonded test boards were subjected to drop tests at a peak acceleration of 1500G with a pulse duration of 0.5ms, and the other half subjected to drop tests at a peak acceleration of 2900G with a pulse duration of 0.3ms. Half of the test boards without edge bonding were subjected to drop tests at a peak acceleration of 900G with a pulse duration of 0.7ms, and the other half subjected to drop tests at a peak acceleration of 1500G with a pulse duration of 0.5ms. Two drop test failure detection systems were used in this study to monitor the failure of solder joints: a high-speed resistance measurement system and a post-drop static resistance measurement system. The high-speed resistance measurement system, which has a scan frequency of 50KHz and a 16-bit signal width, is able to detect intermittent failures during the short drop impact duration. Statistics of the number of drops to failure for the 15 component locations on each test board are reported. The effect of component position on drop test reliability is discussed. The test results show that the drop test performance of edge-bonded CSPs is five to eight times better than the CSPs without edge bonding. However, the drop test reliability of edge-bonded CSPs with the thermal-cured epoxy is different from that with edge-bonded CSPs with the UV-cured acrylic. The solder crack location and crack area are characterized with the dye penetrant method. The fracture surfaces are studied using scanning electron microscopy (SEM).

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Effect of Pb free Alloy Composition on Drop/Impact Reliability of 0.4, 0.5 & 0.8mm Pitch Chip Scale Packages with NiAu Pad Finish

Cited by 25 publications

References 4 publications

Thermal cycling reliability of SnAgCu solder joints in WLCSP

Thermal cycling reliability of SnAgCu solder joints in WLCSP

‘Effects of Minor Alloying Additions on the Properties and Reliability of Pb‐Free Solders and Joints’

Drop test reliability of lead-free chip scale packages

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