Mangán mikroötvözős forraszanyag mikroszerkezetének vizsgálata elektrokémiai módszerekkel

Jelen munkánk során magánnal adalékolt ón-ezüst-réz alapú ólommentes forraszanyag mikroszerkezetét hasonlítottuk össze hagyományos SAC305 (Sn96.5/Ag3/Cu0.5) forraszanyaggal. A 0,1 a 0,4 vagy 0,7 tömegszázalék mangánt tartalmazó forraszanyagból FR4-es hordozón kialakított tesztmintázaton, újraömlesztéses technológiával forraszdombokat hoztunk létre. A forraszdombokról keresztmetszeti csiszolatot készítettünk, melyeket energiadiszperzív spektrométerrel felszerelt pásztázó elektronmikroszkóppal vizsgáltuk. Speciális elektrokémiai maratási technológiát alkalmazva eltávolítottuk a forrasztott kötések keresztmetszeti csiszolatából a tiszta ón, hogy az intermetallikus finomszerkezetet láthatóvá tegyük. Az így feltárt mikroszerkezet sajátosságait vizsgáltuk a mangánt tartalmazó és hagyományos forraszok esetében. Magas mangán tartalmú kiválásokat láttunk a forrasz tömbi anyagában, melyek szemcsefinomító hatásuk révén hatást gyakorolhatnak a forrasztott kötés mechanikai tulajdonságaira. Továbbá a mangán hatással volt a kialakuló Cu6Sn5 intermetallikus struktúrák morfológiájára. A mangán tartalom hatására hosszú tűkristályszerű képződmények jelentek meg a tömbi anyag teljes térfogatában. Ezen kívül a az Ag3Sn intermetallikus vegyületek ahelyett, hogy ideális esetben a teljes térfogatot átszövő finom szerkezetet hoztak volna létre, a mangán tartalmú szemcsék közvetlen közelében formálódtak

Investigation of the Microstructure of Mn-Doped Tin-Silver-Copper Solder Alloys Solidified with Different Cooling Rates

Due to the moderate price and the non-toxicity, manganese is considered as an ideal dopant for the SAC (SnAgCu) solder alloys. Manganese refines the grain of solder joints, yielding better thermomechanical properties. In present research, the microstructure of the manganese-doped alloys solidified with different technological parameters had been investigated. Sn/Ag0.3/Cu0.7 based solder alloy with three different Mn content (0.1, 0.4, 0.7% wt%) were reflowed on a copper substrate with tempered hot plate. They were solidified with different cooling rates from 0.3 to 4.5 K/s. Cross-sections have been prepared from the solder samples and the metallographic properties of the solder samples was investigated with optical and scanning electron microscopes. The characteristic features of the samples have been compared to conventionally used SAC305 (Sn/Ag3/Cu0.5) solder alloys, solidified with the same rates of cooling. Results showed that besides the grain refinement, the Mn content might also have effect on the evolution of intermetallic layer between the substrate and the solder alloy. The IMC grains of the layer were more elongated and more spalled grains had been observed close to the layer. However, independently of the cooling rate, the microstructure of the Mn containing solder alloys remained the same. This suggests that the macroscopic properties are also expected to be less sensitive to the cooling rate of the solidification

Characterization of Tin Pest Phenomenon in a Low Ag Content SAC Solder Alloy

In the electronics technology, the metallic β-Sn (white tin) is the basic material of solder alloys and surface finishes. The “tin pest” phenomenon is the spontaneous allotropic transition of ß-Sn to the semiconductor α-Sn (gray tin) under the temperature of 13.2°C. In this work, the tin pest susceptibility of the widely used Sn99Ag0.3Cu0.7 solder alloy was investigated and compared to Sn99Cu1 alloy (as a well know reference). Bulk solder bars were prepared by metal casting and the samples were inoculated by InSb, CdTe and α-Sn powders to enhance the allotropic transition process. The inoculator materials were pressed onto the surfaces of the samples by a mechanic lamination. The samples were stored at -10 °C temperature for 8 weeks. The allotropic transition was monitored by optical inspection and by electrical resistance measurements. The microstructural changes of the samples - caused by the transition of crystal structure of Sn – were investigated by metallurgical cross-sections. The results showed, that in all cases the Sn99Ag0.3Cu0.7 solder alloy is much less susceptible to tin pest development than the Sn991Cu, which might be explained by the suppression effect of the Ag alloying. Furthermore, it was found that the process of transition highly depends on the applied inoculator material

Microstructure Influence of SACX0307-TiO2 Composite Solder Joints on Thermal Properties of Power LED Assemblies

The effect of the microstructure of solder joints on the thermal properties of power LEDs was investigated. Solder joints were prepared with different solder pastes, namely 99Sn0.3Ag0.7Cu (as reference solder) and reinforced 99Sn0.3Ag0.7Cu-TiO2 (composite solder). TiO2 ceramic was used at 1 wt% and with two different primary particle sizes, which were 20nm (nano) and 200nm (submicron). The thermal resistance, the electric thermal resistance, and the luminous efficiency of the power LED assemblies were measured. Furthermore, the microstructure of the different solder joints was analyzed on the basis of cross-sections using scanning electron and optical microscopy. It was found that the addition of submicron TiO2 decreased the thermal and electric thermal resistances of the light sources by 20% and 16%, respectively, and it slightly increased the luminous efficiency. Microstructural evaluations showed that the TiO2 particles were incorporated at the Sn grain boundaries and at the interface of the intermetallic layer and the solder bulk. This caused considerable refinement of the Sn grain structure. The precipitated TiO2 particles at the bottom of the solder joint changed the thermodynamics of Cu6Sn5 formation and enhanced the spalling of intermetallic grain to solder bulk, which resulted in a general decrease in the thickness of the intermetallic layer. These phenomena improved the heat paths in the composite solder joints, and resulted in better thermal and electrical properties of power LED assemblies. However, the TiO2 nanoparticles could also cause considerable local IMC growth, which could inhibit thermal and electrical improvements

Effect of current load on corrosion induced tin whisker growth from SnAgCu solder alloys

The effect of current load was investigated on corrosion induced tin whisker growth from SnAgCu (SAC) solder alloys. Three alloys were studied: two low Ag content micro-alloyed SAC and the widely used SAC305. The solder joints were loaded with six different DC current levels between 0 and 1.5A and they were aged in corrosive environment (85 °C/85RH%) for 3000 h. The morphology of the whiskers and the micro-structural changes of the solder joints were examined by scanning electron microscope. It was shown that the current load can decrease the corrosion of the solder joints and consequentially it can decrease whiskering as well

Effect of Cu Substrate Roughness and Sn Layer Thickness on Whisker Development from Sn Thin-Films

The effect of copper substrate roughness and tin layer thickness were investigated on whisker development in the case of Sn thin-films. Sn was vacuum-evaporated onto unpolished and mechanically polished Cu substrates with 1 µm and 2 μm average layer thicknesses. The samples were stored in room conditions for 60 days. The considerable stress – developed by the rapid intermetallic layer formation – resulted in intensive whisker formation, even in some days after of the layer deposition. The developed whiskers and the layer structure underneath them were investigated with both scanning electron microscopy and ion microscopy. The Sn thin-film deposited onto unpolished Cu substrate produced less but longer whiskers than that deposited onto polished Cu substrate. This phenomenon might be explained by the dependence of IML formation on the surface roughness of substrates. The formation of IML wedges is more likely on rougher Cu substrates than on polished ones. Furthermore, it was found that with the decrease of layer thickness, the development of nodule type whiskers increases due to the easier diffusion of other atoms into the whisker bodies