Accelerated thermal cycle

An aging atudy has heen completed which evaluated a number of polymeric materials for potential use as 1) protective coatings for back surfaces of mirrors and 2) solar hellostat edge seals. These investigations were conducted in an artificial weathering chamber that accelerated thermal cycling. We observed the primary mirror failure mode to be silver corrosion resulting from moisture exposure. 

Sharma, S.D. Buddhi, D. Sawhney, R.L. Accelerated thermal cycle test of latent heat-storage materials. Sol Energ 66 (1999) 483-490. 

Silakhori, M. Naghavi, M.S. Metselaar, H.S.C. Mahlia, T.M.I. Mehrali, H. Fauzi, M. Accelerated thermal cycling test of microencapsulated paraffin wax/polyaniline made by simple preparation method for solar thermal energy storage. Materials 6 (2013) 1608-1620. 

Will it survive thermal shock with multiple SBU layers (i.e., solder floats, accelerated thermal cycles, multiple reflows) ... 

The industry test method that is widely used for this testing is IPC-9701 IPC-9701 provides detailed guidelines for the recommended temperature cycling test methods for evaluating the reUabUity of surface-mount solder joints. In addition, IPC-9701 also provides guidelines for estimating the performance of solder joints in different field-use conditions from the recommended accelerated thermal cycling tests. 

Fig. 1 Life data correlations for 100% lead-free SAC assemblies subject to accelerated thermal cycling, (a) Correlation of component characteristic life versus cyclic shear strain range, (b) Correlation of joint characteristic life scaled for solder joint crack area versus cyclic shear strain range.

In conclusion, the backward-compatibility record for SAC balls/Sn-Pb paste assemblies under accelerated thermal cycling conditions is... 

The results for creep of SAC solder suggest that the transition from one dominant creep mechanism to another occurs at a temperature within the range of common operating or accelerated testing conditions, somewhere near 75 °C (167 °F). This temperature-related transition implies that accelerated thermal cycling profiles should be designed carefully... 

The double power-law creep equation (Eq 8) separates the creep component into climb-controlled and combined climb-glide-controlled. During the field use conditions where the thermal excursions are milder and stresses are lower compared to typical accelerated thermal cycling... 

Under field-use conditions or under accelerated thermal cycling qualification conditions, the solder joints experience cyclic thermomechanical loads due to GTE mismatch or thermal gradients among various parts of a packaging assembly and failure due to such thermomechanical loads. In addition to thermomechanical fatigue loads, the solder joints experience stresses due to mechanical loads such as vibration, shock, etc. However, such mechanically-induced failures and other chemically or electrically-induced failures are not the focus of this chapter. 

The thermomechanical models can be validated through various approaches, and in this section, only the most popular approaches are discussed. One approach is to design, fabricate, and assemble a test vehicle, and to subject the test vehicle to accelerated thermal cycling. The test vehicle typically consists of a dummy die or... 

K. Tunga, K. Kacker, R.V. Pucha, and S.K. Sitaraman, Accelerated Thermal Cycling Is It Different for Lead-free Solder , 54th Electronic Components and Technology Conference, June 2004, p 1579-1585... 

Elastic Properties. The strain response of a material to an applied stress will depend on the magnitude of the stress, the components of the stress, the strain rate, and the temperature. Elastic deformation occurs when the strains are proportional to the stresses and when the strains appear and disappear simultaneously with the application and removal of the stresses. Elastic properties used in this study are presented in Table 1. While high lead, 90Pb-10Sn is not included in this chapter s analyses, its properties are included for reference. A en applied consistently, the properties in Table 1 should be appropriate for the range of temperatures seen in accelerated thermal cycling. 

Accelerated Thermal Cycle Testing. The mechanical property data was included as part of the quantitative down-selection process based on a thermomechanical fatigue (TMF) test the test vehicle consisted of a 441/0 leadless ceramic chip carrier (LCCCs-44) with only corner leads soldered to provide conditions for high stress. Test parts were thermally cycled between —55 and + 125 ° C at the rate of 24 cycles per day. The TMF data was expressed as the number of cycles-to-failure for an alloy expressed as a percentage of the cycles-to-failure for eutectic Sn-Pb solder. 

Based on the accelerated thermal cycling test results for the various surface-mounted components in this study, it is clear that the ranking of alloys depends on the thermal stresses... 

The alloy, Sn-3.4Ag. 8Bi, developed and patented by Sandia National Laboratories, was determined in the NCMS Lead-Free Solder Project to exhibit outstanding fatigue properties for surface mount applications under both accelerated thermal cycle test conditions used in the NCMS study. Sandia performed ATC testing of this alloy to 10,000 cycles for 0-100°C with 10°C/min ramp rates and 5-min dwell times [9,10]. There were no electrical failures at end of test (10,000 cycles) for 68 I/O PLCCs, 241/0 SOICs, and 1206 chip capacitors on FR4 boards, no cracks after 5000 cycles, and only minor surface cracks after 10,000 cycles. The Sn-3.4Ag-4.8Bi alloy has demonstrated considerable promise for use in surface mount applications, exhibiting greater fatigue resistance than eutectic Sn-Pb and most other lead-free alloys. It should be... 

FIG. 16 Weibull plots of CSPs with Sn-37Pb balls under accelerated thermal cycle test conditions (—40 to 125°C, with 30-min dwell times at the temperature extremes), as determined by in situ measurements during the JEIDA project. The study evaluated two Pb-free solders and eutectic Sn-Pb as a control. 

A flip-chip technology developed by Toshiba Corporation utilized an ACF to attach bare umbumped chips (with A1 pads) onto a polychlorinated biphenyl (PCB) with bumps formed from a silver paste screen printed on the PCB [32]. After curing, Ag bumps were formed (70 pm diameter, 20 pm height), which were subsequently overplated with Ni/Au. It was determined that an ACF with a low CTE (28 ppm/°C), low water absorption rate (1.3%), and utiUzing a Au-plated plastic ball worked best. It was also found that Ni/Au-plated Ag paste-formed bumps exhibited a lower initial connection resistance and a lower connection resistance increase as compared to Ag paste-formed bumps that were not overplated with Ni/Au. The initial connection resistance for Ni/Au-plated Ag paste bumps and nonplated bumps was 22 and 48 pll, respectively, with a respective increase of 294 and 717 pO after 1000 hr of accelerated thermal cycling (ATC) testing. 

TABLE 11 Cumulative Number of Failures During Accelerated Thermal Cycle Testing... 

In a separate comparative study, accelerated thermal cycle tests (—40°C to 125°C, 14-min dwell time at the extremities, with a 3-min transition) indicated that Sn-3.8Ag-0.7Cu exhibited equivalent or slightly better reliability compared to Sn-Pb-Ag solder interconnections, as shown in Fig. 32. The components (289 I/O, 0.8-mm pitch, PBGAs) were assembled on FR-4 boards... 

FIG. 33 Weibull plot for a 208 I/O CSP accelerated thermal cycle tested in the temperature range from -40°C to 125°C. (Courtesy of Chip Pac, Alpha Metals, Sanmina, Hewlett Packard, Ref. 96.)... 

FIG. 36 Weibull plot for a 2512-sized 0-fi resistor for various solder paste and accelerated thermal cycle test conditions. (Courtesy of Motorola Lead-Free Team, Ref. 94.)... 

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