Silver Sintering Paste Rendering Low Porosity Joint for High Power Die Attach Application

2016 ◽  
Vol 2016 (HiTEC) ◽  
pp. 000134-000142 ◽  
Author(s):  
Sihai Chen ◽  
Christine LaBarbera ◽  
Ning-Cheng Lee
Keyword(s):  
Shear Strength ◽  
Thermal Aging ◽  
Processing Condition ◽  
Total Porosity ◽  
Temperature Cycling ◽  
Large Area ◽  
Die Attach ◽  
Aging Test ◽  
Silver Sintering ◽  
Sintered Ag

Abstract Silver joints with ~10% porosity for die-attach have been achieved with specially engineered Ag sintering pastes, through combined pressureless sintering process plus thermal aging. The pastes developed in this work have the following advantages: 1) they can be used under pressure-less processing condition; 2) they are compatible with conventional reflow oven, resulting in a higher through-put as compared to that of stepwise heating oven; 3) they can be used under air reflow condition; 4) a highly reliable joint has been obtained as judged from the shear strength results from thermal aging and temperature cycling tests. The silver sintering pastes are versatile in bonding different metallization surface including Au, Ag and Cu. It can also be used in bonding large area (10mm × 10mm) dies. Shear test results under varied temperatures implied that the maximum service temperature of Ag sintered joints can be as high as 470 – 530 °C, depending on the shear strength pass criteria, and this is more than 250°C higher than that of high-Pb joints. Thermal aging test at 250°C for the joints generated on Ag-die/Au-DBC combination revealed that Ag continuously consolidates in the bulk phase resulting in the formation of larger pores with reduced numbers as compared to that of untreated samples. At the same time, it diffuses to sintered Ag/Au-DBC interface to form a dense Ag layer induced by alloying with Ni(Au) and Cu, which strengthened the bonding. A large bondline thickness is critical for obtaining highly reliable joints. The total porosity of the joint is found slightly decreased during the course of 3200h aging test. Temperature cycling at −55 °C to 200°C shows that the silver joints are stable for at least 1000 cycles.

Highly Reliable Pressure-Less Silver Sintering Joints

2018 ◽  
Vol 2018 (HiTEC) ◽  
pp. 000045-000050 ◽  
Author(s):  
Sihai Chen ◽  
William Shambach ◽  
Christine LaBarbera ◽  
Ning-Cheng Lee
Keyword(s):  
Shear Strength ◽  
Adhesion Strength ◽  
High Reliability ◽  
Total Porosity ◽  
Sintered Sample ◽  
Bond Line ◽  
Temperature Cycling ◽  
Mode Analysis ◽  
Interface Temperature ◽  
Silver Sintering

Abstract Pressure-less silver sintering pastes with high reliability tested by temperature cycling test (TCT) under −40°C to 175°C were developed. The silver joints formed between Si die and Si3N4 active metal brazing (AMB) substrate can survive at least 1500 cycles without decrease in shear strength. In contrast, the strength of reference solders decreases to 62% to 86% of their initial values. The optimized silver joints can achieve average total void% of <1.3% and maximum single void% of <0.3%. Die tilt angle can be controlled within < 0.3°. Failure mode analysis of the joints reveals that during TCT in the bulk phase, silver sintering continues resulting in the formation of larger grain and pore size; while at the interface, the adhesion strength at the silver-substrate interface was gradually enhanced as compared to that at the silver-Si interface. Temperature cycling makes the adhesion strength at both interfaces more balanced accounting for the constant shear strength. SEM cross-section shows that for the as-sintered sample the porosity within the joint is not evenly distributed; the center area normally has a low porosity of < 4%, while at the edge there is a higher porosity of 18% to 24%. The average total porosity of the joint is ~ 13%. This value does not change after 800 cycles of TCT, but increases to 19% at 1500 cycles. The effect of TCT on the joints under conditions such as different surface finished substrate, varied bond line thickness and Si die size was also studied.

PRESSURELESS SINTERING OF NANO- AG PASTE WITH LOW POROSITY FOR DIE ATTACH

2014 ◽  
Vol 2014 (1) ◽  
pp. 000092-000098 ◽  
Author(s):  
Sihai Chen ◽  
Guangyu Fan ◽  
Xue Yan ◽  
Chris LaBarbera ◽  
Lee Kresge ◽  
...  
Keyword(s):  
Shear Strength ◽  
Thermal Aging ◽  
Migration Rate ◽  
Dense Layer ◽  
Pressureless Sintering ◽  
Thermal Shock Test ◽  
Sintering Process ◽  
Shock Test ◽  
Die Attach ◽  
Ag Paste

A novel nano-Ag sintering paste C has been developed for a pressureless sintering process under air. Paste C was sintered at 250°C (C1) and 280°C (C2), respectively; C1 showed a slightly higher porosity but higher shear strength after aging at 250°C for 840 hours. Both C1 and C2 exhibited a microstructure much more stable than the control solder 92.5Pb/5Sn/2.5Ag, which suffered both IMC spalling after thermal aging and voiding. Ag migration toward the DBC to form a dense layer of AgCuNi(Au) was observed for all nano-Ag pastes that were studied, with C1 and C2 being more moderate in the migration rate. The Ag migration could be attributed to the tendency of Ag to form an alloy with Au, with abundant Ni and Cu at the DBC side, and appeared to be affected by the chemistry of nano-Ag paste. A liquid to liquid thermal shock test from −45°C to 240°C was attempted, and was considered too harsh for the die/DBC system employed in this study.

Development of BiAgX® HT Solder Paste for 200°C Application

2016 ◽  
Vol 2016 (HiTEC) ◽  
pp. 000128-000133 ◽  
Author(s):  
Hongwen Zhang ◽  
Jonathan Minter ◽  
Ning-Cheng Lee
Keyword(s):  
Shear Strength ◽  
Thermal Cycling ◽  
Melting Temperature ◽  
Thermal Aging ◽  
Joint Strength ◽  
Solder Paste ◽  
Thermal Cycling Test ◽  
Cycling Test ◽  
Die Attach ◽  
Board Level

Abstract BiAgX® paste with the remelting temperature around 262°C has been tested and adopted successfully for die attach applications [1–5]. BiAgX® HT pastes with the enhanced remelting temperature above 265°C have been designed for the application of 200°C or even higher. The joint strength has been well maintained for most of the tested pastes after thermal aging @ 200°C for 1000hrs. The thermal cycling test (from −55°C to 200°C) degrades the bond shear strength but some of the tested pastes can still keep the joint strength well above IEC standard (IEC 60749-19) required. The melting temperature and the reliability have been observed to closely associate with the alloying elements Z%wt. The BiAgX® pastes have also been modified for board level assembly application. BiAgX® solder wire is under development too.

Evaluation of Pressure Free Nanoparticle Sintered Silver Die Attach on Silver and Gold Surfaces

2013 ◽  
Vol 2013 (HITEN) ◽  
pp. 000237-000245 ◽  
Author(s):  
G. Lewis ◽  
G. Dumas ◽  
S. H. Mannan
Keyword(s):  
Shear Strength ◽  
Cross Sections ◽  
Storage Time ◽  
Sintering Process ◽  
Die Attach ◽  
Free Process ◽  
Sintered Ag ◽  
Bondline Thickness ◽  
Ag Substrate ◽  
Thickness Measurements

A commercially available silver nanoparticle based die attach material was used in a pressure free process to bond 2.5 mm square Ag plated Si die to Ag and Au plated substrates. The two substrate types were 5mm square Ni/Ag plated silicon substrate and a W/Ni/Au metallised cofired alumina package. The assemblies were stored at 300 °C for up to 500 h and the morphology of the sintered Ag and the shear strength was monitored as a function of time. Bondline thickness measurements were carried out after following the paste manufacturer's drying and sintering temperature profile. On Ag substrate it was found that die shear strength increased with storage time. The fracture surfaces of the sheared die and substrate as well as cross sections of untested die were examined using electron microscopy. It was found that the Ag grains grew in size and porosity decreased over time. There was also a clear difference in morphology between sintered Ag at the die edge and centre. During shearing the Ni layer was found to separate from the chip at the edges of the die after ageing. On Au substrate, it was found that die shear strength decreased with storage time. It was found that the Au diffused into the Ag, creating a low porosity Au-Ag layer. Ag also migrated towards the Au surface, leaving behind a layer of voids which contributed to weakening of the joint. Rapid Au diffusion was associated with the high density of grain boundaries arising from the sintering process.

High reliable and high bonding strength of silver sintered joints on copper surfaces by pressure sintering under air atmosphere

2018 ◽  
Vol 2018 (1) ◽  
pp. 000434-000441
Author(s):  
Ly May Chew ◽  
Wolfgang Schmitt
Keyword(s):  
Shear Strength ◽  
High Temperature ◽  
Temperature Cycling ◽  
Acoustic Microscopy ◽  
Sintering Process ◽  
Copper Surfaces ◽  
Air Atmosphere ◽  
High Temperature Storage ◽  
Silver Sintering ◽  
Temperature Storage

Abstract Silver sintering is a promising die attach technology for high temperature power electronics packaging. Our previous studies have revealed that highly reliable sintered joints was obtained on silver and gold surfaces by either non-pressure or pressure sintering. In this paper, we extended our study to die attachment on copper surfaces by pressure sintering under air atmosphere. We attached Ag metallized die on silicon nitride active metal braze copper substrates with Ag metallization and without metallization by silver sintering at 230°C with a pressure of 10 MPa for 3 min. We observed that the average initial die shear strength for bare Cu substrate is lower than for Ag metallized substrate. This observation is attributed to the self-diffusion of Ag is faster than the interdiffusion between Ag and Cu. However, the average die shear strength for all samples increased considerably after temperature cycling test (−40°C/+150°C) and high temperature storage at 250°C. It is highly likely that sintering process is not yet completed under the sintering conditions used in this study and consequently Ag and Cu continued to diffuse during thermal cycling and high temperature storage and as a result strengthen the sintered joints. It is believed that after a certain time of storage at 250°C the sintering process is completed as we observed the average die shear strength remained relatively constant after 250 h storage. Voids, drying channels and delamination in the sintered joints were not detected by scanning acoustic microscopy for the samples before and after 2000 thermal cycles.

Reliability of High-Power Light Emitting Diode Attached With Different Thermal Interface Materials

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
Xin Li ◽  
Xu Chen ◽  
Guo-Quan Lu
Keyword(s):  
High Power ◽  
Heat Dissipation ◽  
Light Emitting Diode ◽  
Temperature Cycling ◽  
Fluorescent Light ◽  
Light Sources ◽  
Light Emitting ◽  
Die Attach ◽  
Nanosilver Paste ◽  
Interconnection Material

As a solid electroluminescent source, white light emitting diode (LED) has entered a practical stage and become an alternative to replace incandescent and fluorescent light sources. However, due to the increasing integration and miniaturization of LED chips, heat flux inside the chip is also increasing, which puts the packaging into the position to meet higher requirements of heat dissipation. In this study, a new interconnection material—nanosilver paste is used for the LED chip packaging to pursue a better optical performance, since high thermal conductivity of this material can help improve the efficiency of heat dissipation for the LED chip. The bonding ability of this new die-attach material is evaluated by their bonding strength. Moreover, high-power LED modules connected with nanosilver paste, Sn3Ag0.5Cu solder, and silver epoxy are aged under hygrothermal aging and temperature cycling tests. The performances of these LED modules are tested at different aging time. The results show that LED modules sintered with nanosilver paste have the best performance and stability.

Large-area Nanosilver Die-attach by Hot-pressing Below 200°C and 5 MPa

2012 ◽  
Vol 2012 (HITEC) ◽  
pp. 000129-000134 ◽  
Author(s):  
Kewei Xiao ◽  
Jesus N. Calata ◽  
Hanguang Zheng ◽  
Khai D.T. Ngo ◽  
Guo-Quan Lu
Keyword(s):  
Atmospheric Pressure ◽  
Hot Pressing ◽  
Applied Pressure ◽  
Fractional Factorial ◽  
Maintenance Cost ◽  
Pressing Pressure ◽  
Hot Press ◽  
Large Area ◽  
Die Attach ◽  
Temperature Time

Sintered nanoscale silver joint is an emerging lead-free die-attach solution for high-temperature packaging because of silver's high melting temperature. For bonding small chips, the nanosilver solution can be achieved with a simple heating profile under atmospheric pressure. However, for bonding large-area chips, e.g. > 1 cm2 IGBT chips, uniaxial pressure of a few MPa has been found necessary during the sintering stage of the bonding process, which is carried out at temperatures below 275°C. Hot-pressing at high temperatures can cause significant wear and tear on the processing equipment, resulting in high maintenance cost. In this study, we ran a series of experiments aimed at lowering the hot-pressing temperature. Specifically, we examined a process involving hot-press drying, followed by sintering without any applied pressure. A fractional factorial design of experiments was used to identify the importance and interaction of various processing parameters, such as hot-pressing pressure/temperature/time and sintering temperature/time, on the final bond quality of sintered nanosilver joints. Based on the results, a simpler process, consisting of hot-press drying at 180°C under 3 MPa, followed by sintering at 275°C under atmospheric pressure was found to produce attachments with die-shear strength in excess of 30 MPa.

Energy and Eco-Sustainability using Pressure-less Silver Sintering for RF Power Electronics

2019 ◽  
Vol 2019 (1) ◽  
pp. 000344-000359
Author(s):  
Evan A. Hueners ◽  
Richard D. Hueners ◽  
Anthony D. F. O' Sullivan ◽  
M. Redzuan Zin
Keyword(s):  
Power Electronics ◽  
High Speed ◽  
Bond Line ◽  
Acoustic Microscopy ◽  
Rf Power ◽  
Technical Requirements ◽  
Die Attach ◽  
Effective Manner ◽  
Confocal Scanning ◽  
Silver Sintering

Abstract Energy & Eco-Sustainability using Pressureless Silver Sintering for RF Power Electronics A virtually void free die attach was successfully achieved using a fixed but critical volume of Ag sinter paste by a process of pressureless sintering on a multi-axis cartesian style bonder, retro-fitted with with a high-speed jetting dispenser. While this process potentially offered an ideal combination of cost-effectiveness, control and speed, it required the development of additional software protocols to secure the level of performance demanded of the dispenser to meet exacting technical requirements. This proprietary adaptation we term “Fixed BLT” software, and over five test pieces we were consistently able to deliver a fixed height bond-line of circa 70% of bond height, translating as 50 um before sinter and 30 um after. In each case the result was a virtually bond free void secured in a timely, repeatable, commercially effective manner. The absence of voids was verified through industry standard non-destructive analysis utilizing confocal scanning acoustic microscopy (CSAM).

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