Basic Information for Sn Name: Tin Symbol: Sn Atomic Number: 50 Atomic Mass: 118.71 amu Melting Point: 231.9 C (505.05 K) Boiling Point: 2270.0 C (2543.15 K) Number of Protons/Electrons: 50 Number of Neutrons: 69 Classification: Other Metals Crystal Structure: Tetragonal Density @ 293 K: 7.31 g/cm3 Color: white Basic Information for Pb Name: Lead Symbol: Pb Atomic Number: 82 Atomic Mass: 207.2 amu Melting Point: 327.5 C (600.65 K) Boiling Point: 1740.0 C (2013.15 K) Number of Protons/Electrons: 82 Number of Neutrons: 125 Classification: Other Metals Crystal Structure: FCC Density @ 293 K: 11.34 g/cm3 Color: bluish
Pb-Sn Phase Diagram (a) (b) http://www.ami.ac.uk/courses/topics/0128_sm/index.html A schematic drawing for measuring the wettability of solder (a) to measure wetting angle and (b) to ensure wetting force. www.dklmetals.co.uk/factorfiction.pdf
Alternative basis metals to lead and their alloys A Zoran Miric and A Grusd: Soldering & Surface Mount Technology 10/1 [1998] 19 25
A typical reflow profile for Sn63Pb37 solder. The reflow profile is a critical part of the solder process and must provide adequate time for flux volatilization, proper peak temperatures, and time above liquidus. A typical reflow profile is made up of four distinct zones. 1) Preheat Zone : The heating rate in the preheat zone should be 2 C to 4 C/second and the peak temperature in this zone should be 100-125 C. 2) Soak Zone: The soak zone is intended to bring the temperature of the entire board up to a uniform temperature to minimizing temperature gradients. The soak zone also acts as the flux activation zone for solder paste. Soak times are usually around the range of 130-170 C for 60 to 90 seconds. 3) Reflow Zone : In this zone the temperature is kept above the melting point of the solder for about 30 to 60 seconds. The peak temperature in this zone should be high enough for adequate flux action and to obtain good wetting. A peak temperature range of 215-220 C is generally considered acceptable. 4) Cooling Zone : The cooling rate of the solder joint after reflow is also important. The faster the cooling rate, the smaller the grain size of the solder, and hence the higher the fatigue resistance of the solder joint. Unfortunately, cooling too fast will result in residual stresses between TCE (Thermal Coefficient of Expansion) mismatched components. So the cooling rate needs to be optimized. www.anadigics.com/content/download/.../solderreflowreport.pdf
How candidate lead-free alloys could be modified to improve their performance as solders; it is necessary to look more closely at how they differ from tin-lead solder A significant difference between these lead-free solders and tin-lead in that the other phases in their eutectics are intermetallic compounds rather than simple metallic solid solutions. Although the tin-rich and lead rich phases in the tin-lead eutectic are crystalline they do not grow in a form that is recognisable as crystalline. The intermetallic compounds in the Sn-Cu and Sn-Ag-Cu systems, Cu 6 Sn 5 and Ag 3 Sn grow in a faceted manner to form structures that are distinctly crystalline in appearance, needles in the former case and plates in the latter. Probably because that faceted growth is difficult to nucleate the coupled growth that is characteristic of a eutectic does not normally occur www.dklmetals.co.uk/factorfiction.pdf
Liquidus temperature of some lead-free solders compared with that of Sn63Pb37 www.dklmetals.co.uk/factorfiction.pdf
It is important that the melting point of lead-free solder be as close as possible to that of the tin-lead solder it replaces. There were no element in the Periodic Table that would reduce the melting of tin as low as did lead, i.e. from 232 C to 183 C. Bismuth at the level of 57% could lower the melting point even further to 139 C but the resulting alloy is difficult to use. Zinc at the level of 9% lowers the melting point to 198 C Copper reduces the melting point only a few degrees to 227 C, still 44 C higher than that of tin-lead solder. The addition of silver to tin-copper reduces the melting point a further 10 C to 217 C. Tin-silver-copper alloy have been widely accepted as the preferred leadfree option. Those concerned that 217 C was still too high for a practical tin-lead replacement made further additions of elements such as bismuth and indium but these increased the cost and/or compromised other properties or the recyclability, which was one of the main reasons for elimination of lead. Practical experience has indicated however, that a melting point close to that of tin-lead was not as important as first thought. www.dklmetals.co.uk/factorfiction.pdf
Sn & Sn-Alloy Sn coated plate 저융점 연질이므로 앏은 박으로 사용 무독성, 의약품 식품 등의 tube 상온가공경화가 없어 소성가공이 쉽다.(재결정온도 상온이하) 지금순도 99.8% 1)물리적 성질 Sn - 백색주석(β-Sn ; bct) 회색주석(α-Sn ; cubic) (변태온도가 13.2 C 이나 시간적 지체 때문에 40 C 에서, 고순도 주석 -10 C 부 근에서 변태 됨) Bi, Pb, Sb 변태지연, Zn, Al, Mg, Co 변태촉진 2)기계적 화학적 성질 고온에서는 강도, 경도, 연신율 모두 β-sn은 금속중 Pb 다음으로 soft 쉽게 박 굽히면 tin cry 소리 Sn의 내식성 산소의 존재에 의해 내식성
Sn & Sn-Alloy Soft solder (땜납) Cu, brass, bronze, Fe, Zn의 접합제 - 300 이하의 용해온도 주로 Sn Pb계 합금조성에 따라 용해온도, 응고온도범위가 달라진다. 1)고온용: Sn alloy(95sn5ag), Cd(95Cd5Ag) or Zn(83Cd17Zn)계 alloy 2)저온용: Sb(β α변태 억제) 함유 Sn alloy저온용 적합(95Sn5Sb) Pb의 함량이 많은 alloy 적합 3)기타합금 경석( Hard Sn) ;0.4%Cu첨가된 Sn 의약품, 그림물감등에 대한 내식성 우수 Tube, slab으로 주조하여 냉간압연으로 plate (판) extrusion하여 성형 주조용품 Sn alloy; 4~7%Sb 1~3%Cu함유 Pewter나 Britania metal장식용품에 이용
Pb & Pb-Alloy 역사적인 재료 (융점이 낮고 가공이 용이) battery 전극, Solder용, cable피복, 활자합금, bearing합금 밀도가 크다 (11.36g/cm3) FCC (a=4.9389) 연하고ductility가 좋다. M.P가 낮다(327.4 ) 방사선 차단력이 강하다. 내식성 우수 관, 판으로 널리 이용 원래 반응성이 강하고 수소이온과 치환하기 쉬운 금속이나 불용 해성 피복이 표면에 형성( 탄산염, 규산염의 보호피막 형성 보통 의 물)
Pb & Pb-Alloy 1) Pb-As (cable 피복용, Arsenical lead) 0.12 ~ 0.2%As, 0.08~0.012%Sn, 0.05~0.15%Bi 강도, 내creep성질이 Pb보다 우수 고온에서 extrusion가공 water quenching강도가 증가 creep rate 25 C 0.21kg/mm2의 T.S에서 0.13%year 2) Pb Sb alloy Sb의 고용도 온도에 따라 크게 변화 주물 후 or 열간압출가공 후 시효경화한다. Sb의 첨가 강도증가 Cu, Te첨가 결정립 미세화, g.b석출에 의한 피로강도의 저하 억제 1% Sb (antimonial lead) cable 피복용 4~8%Sb (경석, hard lead) Sb%가 낮은 alloy 관, 판 가공용 Sb%가 높은 alloy 주물용 9%Sb 축전지 전극 격자용
Two small vials of liquid metal. The vial on the right contains gallium, an element that melts at 29.76 C. The vial on the left is an alloy that contains gallium, indium, and tin, and melts at -20 C. http://sci-toys.com/scitoys/scitoys/thermo/thermo4.html
Pb & Pb-Alloy 3) Fusible alloy (저융점 합금) 250 이하 m.p. Pb, Bi, Sn, Cd, In등의 alloy 비교적 m.p.가 낮은 alloy (Bi를 많이 함유) - 공정조성합금(Eutectic alloy)이 이용 - 비공정조성합금(non-eutectic alloy) : 응고 온도 범위가 넓어서 실용상 고체로서의 강도가 거의 소멸 하는 온도 항복온도(yield temperature) https://www.inventables.com/technolo gies/low-temp-fusible-alloy 용도 : 화재통보기, 압축공기용 탱크 안전밸브, 방화문체결구, 광휘소둔로의 액체 seal, 저온 땜납