1. Due to your snooping roommate, you decide to build a circuit for an electroni
ID: 902980 • Letter: 1
Question
1. Due to your snooping roommate, you decide to build a circuit for an electronic buzzer. Digging around, you found some solder (composition 90wt% Pb, 10% Sn) and a soldering iron. Attempting the soldering process revealed that the solder doesn’t melt, no matter how long you put the soldering iron on it. Apparently, your soldering iron has a maximum temperature of only 250 °C. If you have 30 grams of the 90/10 solder, how much tin would you need to add in order to solder the circuit? Assume soldering requires complete melting of the alloy.
2. Describe, using diffusion concepts, the best method to add the amount of tin calculated in #1.
3.A notice appeared on your front door – apparently your sidewalk is covered in ice and posing a hazard. Being poor college students, how much will it cost to melt the ice?
-Your sidewalk is 1 m wide, 20 m long, and has (on average) a 2 mm thick ice coating.
-The outside air temperature will not get above -15 °C any time soon.
-Salt costs $1.60/kg.
-Assume ice has a density of 0.92 g/cm3
-Phase diagram that may be helpful is on page 378 (4th Edition).
4. In the circuit you just built, you unfortunately made it so the solder acts as a load-bearing support. Your entire buzzer system has a mass of 15 kg. Given that the lead-tin solder has a tensile strength of 52.5 MPa, an average solder size of 1 mm in diameter, and 3 solder junctions that have a load upon them, will your device fail?
5. Draw the plots of the energy change for nucleation as a function of nucleus size for homogeneous and heterogeneous nucleation, assuming a temperature slightly less than the melting temperature. Redraw this curves assuming a greater degree of undercooling. Does heterogeneous nucleation change the critical radius size? Why or why not?
Explanation / Answer
Post multiple question to get the answer to the remaining parts
1) Amount of Solder = 30 gms
Percentage of tin in solder = 10% wt of solder (Since the ratio of lead : tim is 90% wt : 10% wt)
Amount of tin required = 10/100 * 30 = 3 gms
Hence we require 3 gms of tin to make 30 gm of solder
2) The best method is to add the tin using Facilitated Diffusion
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