Qualification of SnAg solder bumps for lead-free flip chip applications

2004 ◽  
Author(s):  
B. Ebersberger ◽  
R. Bauer ◽  
L. Alexa
Keyword(s):  
Flip Chip ◽  
Lead Free ◽  
Solder Bumps ◽  
Snag Solder

Study on electromigration in flip chip lead-free solder connections with 40 μm or 30 μm diameter on thin film ceramic substrates

2015 ◽  
Vol 2015 (1) ◽  
pp. 000799-000805
Author(s):  
Marek Gorywoda ◽  
Rainer Dohle ◽  
Bernd Kandler ◽  
Bernd Burger
Keyword(s):  
Thin Film ◽  
High Stability ◽  
Flip Chip ◽  
Lead Free ◽  
Published Data ◽  
Organic Substrates ◽  
Lead Free Solder ◽  
Ceramic Substrates ◽  
Solder Bumps ◽  
Free Solder

Electromigration comprises one of the processes affecting the long-term reliability of electronic devices; it has therefore been the focus of many investigations in recent years. In regards to flip chip packaging technology, the majority of published data is concerned with electromigration in solder connections to metallized organic substrates. Hardly any information is available in the literature on electromigration in lead-free solder connections on thin film ceramic substrates. This work presents results of a study of electromigration in lead-free (SAC305) flip chip solder bumps with a nominal diameter of 40 μm or 30 μm with a pitch of 100 μm on silicon chips assembled onto thin film Al2O3 ceramic substrates. The under bump metallization (UBM) comprised of a 5 μm thick electroless nickel immersion gold (ENIG) layer directly deposited on the AlCu0.5 trace. The ceramic substrates were metallized using a thin film multilayer (NiCr-Au(1.5 μm)-Ni(2 μm) structure on the top of which wettable areas were produced with high precision by depositing flash Au (60 nm) of the required diameter (40 μm or 30 μm). All electromigration tests were performed at the temperature of 125 °C. Initially, one chip assembly with 40 μm and one with 30 μm solder bumps was loaded with the current density of 8 kA/cm2 for 1,000 h. The assemblies did not fail and an investigation with SEM revealed no significant changes to the microstructure of the bumps. Thereafter seven chip assemblies with 40 μm solder bumps and five assemblies with 30 μm bumps were subjected to electromigration tests of 14 kA/cm2 or 25 kA/cm2, respectively. Six of the 40 μm-assemblies failed after 7,000 h and none of the 30 μm-assemblies failed after 2,500 h of test duration so far. Investigation of failed samples performed with SEM and EDX showed asymmetric changes of microstructure in respect to current flow. Several intermetallic phases were found to form in the solder. The predominant damage of the interconnects was found to occur at the cathode contact to chip; the Ni-P layers there showed typical columnar Kirkendall voids caused by migration of Ni from the layers into the solder. Failure of the contacts apparently occurred at the interface between Ni-P and solder. In summary, the results of the study indicate a very high stability of lead-free solder connections on ceramic substrates against electromigration. This high stability is primarily due to a better heat dissipation and thus to a relatively low temperature increase of the ceramic packages caused by resistive heating during flow of electric current. In addition, the type of the metallization used in the study seems to be more resistant to electromigration than the standard PCB metallization as it does not contain a copper layer.

Electromigration Performance of Flip-Chips with Lead-Free Solder Bumps between 30 μm and 60 μm Diameter

2012 ◽  
Vol 2012 (1) ◽  
pp. 000891-000905 ◽  
Author(s):  
Rainer Dohle ◽  
Stefan Härter ◽  
Andreas Wirth ◽  
Jörg Goßler ◽  
Marek Gorywoda ◽  
...  
Keyword(s):  
Flip Chip ◽  
Failure Modes ◽  
Solder Bump ◽  
Void Formation ◽  
Lead Free ◽  
Large Temperature ◽  
Flip Chips ◽  
Solder Bumps ◽  
Current Densities

As the solder bump sizes continuously decrease with scaling of the geometries, current densities within individual solder bumps will increase along with higher operation temperatures of the dies. Since electromigration of flip-chip interconnects is highly affected by these factors and therefore an increasing reliability concern, long-term characterization of new interconnect developments needs to be done regarding the electromigration performance using accelerated life tests. Furthermore, a large temperature gradient exists across the solder interconnects, leading to thermomigration. In this study, a comprehensive overlook of the long-term reliability and analysis of the achieved electromigration performance of flip-chip test specimen will be given, supplemented by an in-depth material science analysis. In addition, the challenges to a better understanding of electromigration and thermomigration in ultra fine-pitch flip-chip solder joints are discussed. For all experiments, specially designed flip-chips with a pitch of 100 μm and solder bump diameters of 30–60 μm have been used [1]. Solder spheres can be made of every lead-free alloy (in our case SAC305) and are placed on a UBM which has been realized for our test chips in an electroless nickel process [2]. For the electromigration tests within this study, multiple combinations of individual current densities and temperatures were adapted to the respective solder sphere diameters. Online measurements over a time period up to 10,000 hours with separate daisy chain connections of each test coupon provide exact lifetime data during the electromigration tests. As failure modes have been identified: UBM consumption at the chip side or depletion of the Nickel layer at the substrate side, interfacial void formation at the cathode contact interface, and - to a much lesser degree - Kirkendall-like void formation at the anode side. A comparison between calculated life time data using Weibull distribution and lognormal distribution will be given.

Experimental Study of Void Formation in Eutectic and Lead-Free Solder Bumps of Flip-Chip Assemblies

2005 ◽  
Vol 128 (3) ◽  
pp. 202-207 ◽  
Author(s):  
Daijiao Wang ◽  
Ronald L. Panton
Keyword(s):  
Experimental Study ◽  
Heat Flux ◽  
Flip Chip ◽  
Void Formation ◽  
Lead Free ◽  
Void Volume ◽  
Lead Free Solder ◽  
Solder Bumps ◽  
Free Solder ◽  
High Lead

This paper reports the experimental findings of void formation in eutectic and lead-free solder joints of flip-chip assemblies. A previous theory indicated that the formation of voids is determined by the direction of heating. The experiments were designed to examine the size and location of voids in the solder samples subject to different heat flux directions. A lead-free solder (Sn-3.5Ag-0.75Cu) and a eutectic solder (63Sn37Pb) were employed in the experiments. Previous experiments [Wang, D., and Panton, R. L., 2005, “Experimental Study of Void Formation in High-Lead Solder Joints of Flip-Chip Assemblies,” ASME J. Electron. Packag., 127(2), pp. 120–126; 2005, “Effect of Reversing Heat Flux Direction During Reflow on Void Formation in High-Lead Solder Bumps,” ASME J. Electron. Packag., 127(4), pp. 440–445] employed a high lead solder. 288 solder bumps were processed for each solder. Both eutectic and lead-free solder have shown fewer voids and much smaller void volume than those for high-lead solder. Compared with lead-free solder, eutectic solder has a slightly lower void volume and a lower percentage of defective bumps. For both eutectic and lead-free solders, irrespective of the cooling direction, heating solder samples from the top shows fewer defective bumps and smaller void volume. No significant effect on void formation for either eutectic or lead-free solder was found via reversing the heat flux direction during cooling. Unlike high-lead solder, small voids in eutectic or lead-free solder comprised 35-88% of the total void volume. The final distribution of voids shows a moderate agreement with thermocapillary theory, indicating the significance of the temperature gradient on the formation of voids.

Novel flip-chip bonding technology for W-band interconnections using alternate lead-free solder bumps

2002 ◽  
Vol 12 (10) ◽  
pp. 372-374 ◽  
Author(s):  
K. Onodera ◽  
T. Ishii ◽  
S. Aoyama ◽  
S. Sugitani ◽  
M. Tokumitsu
Keyword(s):  
Flip Chip ◽  
Lead Free ◽  
Lead Free Solder ◽  
Flip Chip Bonding ◽  
W Band ◽  
Solder Bumps ◽  
Bonding Technology ◽  
Free Solder

A novel bumping process for fine pitch Sn–Cu lead-free plating-based flip chip solder bumps

2007 ◽  
Vol 10 (4-5) ◽  
pp. 133-142 ◽  
Author(s):  
Jung-Tang Huang ◽  
Pen-Shan Chao ◽  
Hou-Jun Hsu ◽  
Sheng-Hsiung Shih
Keyword(s):  
Flip Chip ◽  
Lead Free ◽  
Fine Pitch ◽  
Solder Bumps

Evaluation of lead-free SnAg solder ball deposition and reflow processes for flip chip applications

2005 ◽  
Vol 82 (3-4) ◽  
pp. 581-586 ◽  
Author(s):  
Johann Helneder ◽  
Charlotte Hoyler ◽  
Manfred Schneegans ◽  
Holger Torwesten
Keyword(s):  
Solder Ball ◽  
Flip Chip ◽  
Lead Free ◽  
Snag Solder

Development of Lead Free Plating Chemical for Various Applications

2012 ◽  
Vol 2012 (DPC) ◽  
pp. 000944-000967
Author(s):  
Takeshi Hatta ◽  
Atsushi Ishikawa ◽  
Takuma Katase ◽  
Akihiro Masuda
Keyword(s):  
Chemical Stability ◽  
High Speed ◽  
Flip Chip ◽  
New Technologies ◽  
High Reliability ◽  
Lead Free ◽  
Current Status ◽  
Chip Technology ◽  
Solder Bumps ◽  
Pure Sn

Flip chip connection has been applied to a lot of applications to shorten the connection length for high performance. Solder bumping is one of the key technologies for flip chip connection, and its quality strongly brings large impact on the reliability after packaging. Electroplating is one of the methods to form solder bumps. And Sn-Ag is considered as the first candidate of lead free alloy for electroplating method. We have released Sn-Ag plating chemical and it has been used by many customers in the world. In the future, flip chip technology will progress to further miniaturization and high integration with the new technologies such as Cu pillar and Through Silicon Via (TSV). At that time, further variations of alloys are necessary for electroplating method to meet various requirements. Even for Sn-Ag plating chemical, higher plating rate is required to improve productivity in mass production. In this time, we have developed new Sn-Ag high speed plating chemical based on our conventional technology. Furthermore, we have succeeded to develop Pure Sn and Sn-Cu chemicals for bumping method to meet customer's requirement. Sn-Cu is considered as a good candidate for bumping alloy to achieve high reliability, but the chemical stability is not so good. Therefore, we successfully modified the Sn-Cu chemical and extended chemical stability. We will update our current status about high speed Sn-Ag plating chemical and other chemicals like Sn-Cu and pure Sn in this time. By using these binary alloy chemicals, we are able to produce Sn-Ag-Cu solder bumps by stacking Sn-Ag and Sn-Cu. And it can bring further variation for bumping alloys.

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