Page 86
www.us-
tech.com
February, 2020 Nihon Superior SN100CV —Reliability in Simplicity Continued from previous page
the elements of which can diffuse into the solder, and perhaps react to form new phases. The small intermetallic particles that form in
the interdendritic eutectic during solidification have a high surface-to-area volume ratio. There is a thermodynamic drive toward growth of larger particles at the expense of smaller ones. Since it is the smaller particles that are the
most effective obstacles to disloca- tion movement, as the coarsening proceeds, the strengthening effect of the precipitate-forming addi- tives fades. This decline in reliabil- ity with aging is particularly apparent in solder alloys that rely on silver for their strength. The fine particles of eutectic
Ag3Sn intermetallic lose their strengthening effect as the ther-
modynamic drive to reduce their surface-to-area volume ratio re - sults in larger particles growing at the expense of smaller particles that eventually disappear. As the gap between the parti-
cles increases, their effectiveness as obstacles to dislocation move- ment fades and the particle strengthening effect is lost. The solubility in tin of ele-
ments added to provide solid solu- tion strengthening can be very sen- sitive to temperature, typically declining to low levels at room temperature. When the solder joint freezes quickly, there is not enough time for the solute atoms to redistribute so that the tin matrix can be supersaturated. That means the soldered joints have a degree of solid solution strengthening that creates an expectation of relia- bility that cannot be sustained as the joint ages. The relatively low melting point of solder alloys means that even at room temperature they
Comparison of shear strength of various components over cycles from 0 to 2,000 at –40 to +257°F (–40 to +125°C), 15 minute dwells.
tion strengthening means that even over the temper- ature range of a typical in-service thermal cycle the strengthening element will be driven in and out of solution, with precipitates forming at room tempera- ture and at least partly redissolving as the tempera- ture increases during each thermal cycle.
SN100CV. High strength. Silver-free. Nihon Superior has enhanced the reliability of
are at an homologous temperature equivalent to, say, copper at 1,022°F (550°C), which means that the diffusion processes that drive the system to thermodynamic equilibrium occur quite rapidly with consequent loss of solid solution strengthen- ing and the formation of new phases that are rich in the solute element. The temperature sensitivity of the solubility in the tin matrix of elements added to provide solid solu-
its popular SN100C alloy to add a relatively high degree of compliance and microstructural stability. This means the use of solid solution strengthening, rather than particle hardening with the level of the solute addition being kept within the solid solubility limit at normal service temperatures. The resulting alloy, SN100CV, is targeted at
applications that require a better retention of strength than conventional SAC alloys. Being sil- ver-free, SN100CV also can also be obtained at a lower cost than SAC alloys. The simpler, more stable
microstructure of SN100CV, when compared with an alloy with a higher bismuth content can be seen in Figure 1 (page 83). The light areas in the interdendritic spaces of Figure 1 (right) are from bismuth that will largely go into solution at the peak temperature of a thermal cycle, and re-precipi- tate in the tin when cooling. Bismuth has an inhibiting
effect on the creep strain that drives solder joint failure. The ini- tial particle-strengthening effect of the silver in SAC305 is lost quickly at 257°F (125°C) and deformation to failure proceeds much faster than for SN100CV. With a formulation that
builds on the success of Nihon Superior’s SN100C, the controlled
addition of bismuth in SN100CV delivers perform- ance superior to that of SAC305, without the cost of silver. Contact: Nihon Superior USA, LLC, 1395
Hawk Island Drive, Osage Beach, MO 65065 E-mail:
k.howell@
nihonsuperior.co.jp Web:
www.nihonsuperior.com r
See at IPC APEX, Booth 2043
See at IPC APEX, Booth 3535
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144
