Lab 4 Soldering

Outcome of this lab
1. Understand how IR emitters and receivers work.
2. Practice soldering,

1. Instruction for soldering

Task 1: Read the following instruction and prepare for your soldering work.

1.1. 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.

1.2. 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.

1.3. 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, and my lab at FLC. 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)

1.4. 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.

2. Build a light sensing circuit on a prototype PCB board

A photoresistor (or light-dependent resistor, LDR, or photo-conductive cell) is a light-controlled variable resistor. The resistance of a photoresistor decreases with increasing incident light intensity; in other words, it exhibits photoconductivity. A photoresistor can be applied in light-sensitive detector circuits, and light-activated and dark-activated switching circuits.


Parts Required & Circuit Diagram:
10k potentiometer,
10k & 1k LDR
741 Comparator op-amp
9V voltage source

A potentiometer is an electrical component/device that can be adjusted to provide an on-demand resistance (in a certain range) in a cicuit. Picutres of potentiometers and schematic of them can be found in the following figures:

This is a Light sensor circuit. Probably most simple and interesting circuit to play with. It can be configured as either shadow detector or Light detector, which means it can detect the intensity of light. Right now in the circuit diagram it is configured as a Shadow Detector, that means the LED will turn on when we show a bright light over LDR. We can change this circuit as Light Detector by simply swapping the pins 2 & 3 of 741 Comparator IC, and then LED will turn on when LDR is dark. In this circuit, please make sure that pins no 1,5 & 8 are not connected and left idle. Pin 6 is output pin. In the circuit it is connected to an LED via 1K resistor, but you can also connect a transistor to turn on a relay, motor or any other output.

The Pin map of the 741 chip is:

Task 2: Build this circuit on a prototype board. Solder the components onto the board. Make sure use IC sockets for the 741 chip. Test your circuit and reord demonstration videos for the lab report.

3. Practice on soldering Surface Mount (SMT) components.

The instructor will provide some PCB board with SMT components for students to practice.

Task 3: Demonstrate that you are able to solder a SMT resistor to the pads and remove it from the pads on a PCB.

* Show all the hand calculation, simulation, and oscilloscope measurement as required in these tasks in your report for credits.

Follow the lab report guidelines to avoid losing points.