ENGR201 Lab 2018 Fall
Lab 7 Soldering and Capacitors.
Outcome of this lab:
1. Be able to do soldering independently.
2. Observe and analyze the voltage waveforms obtained when charging/discharging a capacitor through a resistor.
3. Observe the frequency response of an RC low-pass filter and high-pass filter.


Instructions:
1. Before soldering:
a. Ensure adequate ventilation. If multiple people are soldering in a concentrated area, set up a fan to gently blow fumes and vapors away from you and your co-workers.
b. Keep area clean around workplace at all times.
c. When working with statically sensitive components (most active devices such as ICs, FETs, transistors, etc.), be sure to use a anti-static mat to work on and wear an anti-static wrist strap to minimize risk of electrostatic discharge (ESD) damage. (Not sure if we will have this ready in the lab this semester, link)

2. Tools
a. Temperature-controlled soldering iron with fine tip (about 1/16" to 1/8" wide).
b. Rosin core solder with a diameter of about 0.032" and a tin-lead (Sn-Pb) content of about 60/40%.
c. A damp (not dry!) sponge for keeping the tip of the soldering iron clean.

3. Soldering
a. Parts to be soldered must be clean. Test the cleanness by pre-tinning wires before soldering them together.
b. Whenever possible, fix the parts to be soldered so that they are not moving during and shortly after soldering.
c. Make sure the tip of the soldering iron is clean! An oxidized tip will not transfer enough heat for the solder to melt fast, but enough to melt plastic and damage printed circuit boards.
d. Apply a small amount of fresh solder to the tip of the soldering iron. Then heat the parts to be soldered and apply solder to the parts (not the iron!) until it melts. Do not move the parts until the solder has cooled down!
e. A good solder joint looks shiny and bright silverish. Do not apply excessive amounts of solder!

An example of a soldering station I used in my graduate school. You may have a slightly different soldering iron, but just show you the components of a typical soldering station:


Minimal thermal linkage due to insufficient solder between the pad and soldering iron tip. A solder bridge provides thermal linkage to transfer heat into the pad and component lead.
     

Solder blends to the soldered surface, forming a small contact angle:


A good solder joint is shown below:


Cold Solder Joints Joints that are dull or convex are potentially “cold” solder joints. Cold solder joints DO NOT make a good electrical or mechanical connection.


A complete set of tools you will need for soldering (not including the iron):


4. Use of Solder Wick
a. Solder wick is typically a ribbon of braided fine copper wire with rosin core flux impregnated into it.
b. To use solder wick, lay the wick over the joint to be de-soldered.
c. Apply the heated tip of the soldering iron to allow the wick to be heated and melt the solder in the joint.
d. The solder will flow out of the joint and into the wick through capillary action.


5. Capacitors:
A capacitor is a passive element designed to store energy in its electric field. Capacitors are used extensively in electronics, communications, computers, and power systems, e.g. in the tuning circuits of radio receivers and as dynamic memory elements in computer systems. A capacitor consists of two conducting plates separated by an insulator (or dielectric), and is determined by the surface area of the plates, the spacing between the plates and the permittivity of the material (i.e. 𝐶 = 𝜖𝐴/𝑑), with a unit of farads (F).
Three types of capacitors:

Characteristics of the three main types of capacitors:


Tasks:
1. Watch the following two videos about soldering:
video 1
video 2

2. Build the folllowing circuit in LTSpice:


a. Explain the parameters in the PULSE() function.
b. Change the values for R and C to: R=1k, C=100n; R=10k, C=10n; did you see any differences in 'delay'? Why? How can you increase/decrease the delay? (only in LTSpice)
c. Derive the equation to calculate the delay of the circuit and compare to your simulation.
d. Use R=100k, C=1 nF, build the circuit on a 'Prototype PCB (Universal Printed Circuit Board)', use an oscilloscope to probe the input & output, and measure the delay. Compare your measurements to your calculation and simulation (organize the calculation, simulation, and measurement data into a table).
Keep in mind that the delay is measured as the 'time' differences between the input and output at the 50% of the input and the output voltage.


An example of soldering on a prototype PCB and its 'Jumping Wires':



3. Build the following circuit in LTSpice: (just a different input of the previous task)

Why the output is attenuated? Can you explain this qualitatively?

What if you decrease the frequency? Does the output increase or decrease? Why? Explain this qualitatively.

What if you increase the frequency? Does the output increase or decrease? Why? Explain this qualitatively.

Build the circuit on the prototype PCB board and change the frequency of the input to show at WHICH frequency the output signal starts being attenuated.

Show your input and output of this circuit on an oscilloscope.

4. Build the following circuit in LTSpice:

Explain qualitatively why the output is attenuated?

What if you decrease the frequency? Does the output increase or decrease? Why? Explain this qualitatively.

What if you increase the frequency? Does the output increase or decrease? Why? Explain this qualitatively.

Build the circuit on the prototype PCB board and change the frequency of the input to show at WHICH frequency the output signal starts being attenuated.

Show your input and output of this circuit on an oscilloscope.




-- The end of the lab