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Lab 04 Soldering

Overview

The focus of this lab is to practice soldering, become familiar with lab equipment and become familiar with safety procedures for safe soldering.

Soldering is the process of using a metal alloy with a low melting temperature to fuse together two other pieces of metal. This is used in all electronics for two reasons: 1. It ensures a strong mechanical connection (i.e. the wires in your computer don’t fall off the circuit board in transit) and 2. Provides a highly conductive electrical connection.

To enhance the “stickiness” of the solder, we use rosin. This is most commonly found within the solder itself but can be applied separately as needed.

Resources/Reading

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Stanford’s Introduction to Soldering⁠

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Soldering Safety

The metal alloy that is most used in soldering is a combination of lead and tin. Yes, that lead. Additionally, the solder contains a rosin flux, which is an organic compound derived from pine trees (you will notice the scent!). Rosin can cause minor eye/respiratory irritation. Finally, the tip of a soldering iron can reach typical temperatures around 660°F to 720° F. Anytime we are working with solder, we will take the following safety precautions:

Wear safety glasses

Wear pants

Wear close-toed shoes

Optional: wear mask

Do not eat or touch face without washing hands

Wash hands with soap before leaving lab

Tips for Successful Soldering

To make a good solder joint you need four things:

Clean leads on each component to be connected. Generally, in lab, component leads are sufficiently clean that no special action need be taken. However, when performing repair work, this will not be the case. More of repair soldering later.

A good mechanical connection. Solder is not that strong and is malleable, so you need a mechanical connection in addition to the solder (electrical) connection. Generally, unless the components are damaged, the components are designed with adequate mechanical strength.

Plenty of heat to warm the wires and melt the solder. Soldering involves heating the component leads/wires and circuit board pads to a sufficient temperature that the solder melts and flows around the mechanical connection.

Soldering is easier and a better connection is made with the soldering iron tip is clean and shiny. Soldering is easier because a clean tip transfers heat to the connection faster than a dirty tip. A better connection is made because there is less chance that crud gets into the connection.

Tools and Equipment

In addition to the safety equipment listed above, be sure that you have the following:

A soldering station including

Base station

Soldering iron

Sponge

Solder

Wire cutters (flush cuts)

Wire strippers

Wire

Helping hands

PCB

Resistors

Solder wick

Tasks

Lap Joints

Obtain all tools and safety equipment

Put on safety equipment

Prepare practice wires

Cut provided wires in half.

Separate the individual strands.

Strip the wires carefully and using the correct tool setting.

The wires are 22 gauge.

The wires are stripped about quarter inch from the end.

Set up the soldering station

Place the soldering iron on the lab bench, ensure that the power switch is off, and plug it into the provided outlet. (note: the soldering iron plugs into the soldering station.)

Be sure that the soldering iron is placed in the metal spring holder.

Power on the soldering station. Set the dial to ‘4’

While the station is heating, dampen the sponge with provided reverse osmosis (RO) water.

Why do we use RO water? It's to prevent mineral and foreign substance buildup. It also improves the reliability of the solder joint since there are no contaminants.

What happens if we use Indiana tap water? The water in Tippecanoe County is very hard and contains lots of naturally occurring minerals. If you were to use this for soldering, the water would corrode the tip of the solder and affect the reliability of the solder joint itself, since there are impurities.

Set up the helping hands

Make sure that your helping hands has at least two alligator clips.

Clean and prepare the soldering iron tip (instructor will demo)

Record notes: When preparing your soldering iron tip, you want to use RO water to eliminate the chance of mineral deposits, wipe the soldering tip on the sponge or pad, then use the bronzer/steel wool to completely clean the tip. Repeat as needed

Tin the wires (instructor will demo)

What is tinning? Tinning is when you add a tiny layer of molten solder at the tip of the wires to prevent fraying and ensure a better mechanical connection.

Record notes:

Tinning is a process that assists in the mechanical connection of solder. In order to tin properly, your iron must be heated up to the correct temperature, and you must ensure all components have been heated sufficiently to allow solder to flow evenly.

Solder the wires (instructor will demo)

Describe what a proper lap joint should look like? The lap joint should be shiny and smooth with the entire joint connecting

Record notes:

The lap joints should have no peaks, the entire wire needs to be covered for good mechanical and electrical connection

Continue to practice lap joins until you have one ready for instructor sign off: ☐ATT

Power off and unplug soldering station allowing it to cool.

Clean up work area and return all tools to their appropriate locations.

Wash hands before leaving lab.

Through Hole PCB

Identify the top of your PCB.

Insert both leads of the resistor into the PCB.

Bend the legs of the resistor slightly to hold it in place.

Following the soldering tips from the Lab Joint section above, apply heat to the resistor leg and soldering pad for about 1 second.

Next feed a small amount of solder into/onto the heated solder pad/component leg.

Hold the soldering iron in place until the solder flows. Describe what a proper through hole solder connection should look like? it should be shiny and look like a volcano. Proper application of the solder would leave no excess behind and completely fill in the through hole.

Continue to practice through hole soldering until you have one ready for instructor sign off: ☐ ATT

Watch this video on using solder wick:

https://www.youtube.com/watch?v=ljRJiN6nHek⁠

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What things do you need to pay special attention to when using solder wick? You must first add flux since it helps to melt the solder and also make sure that you do not overheat the soldering iron. It was recommended to heat the soldering iron at 350C to 400C (662F to 752F).

Using solder wick, remove the solder from the component and hole completely.

Clean Up

Return all components, tools, and equipment to their proper location.

Clean desk surface using provided rubbing alcohol and paper towers.

Reflection

Prior to this lab activity, how would you rank your ability to solder a lap joint?

☐ No knowledge at all.

☐ Very little knowledge – aware that wires can be soldered.

☐ Some knowledge – I have seen someone else solder.

☐ A good about of knowledge – I have soldered before.

☐ Expert knowledge – I have soldered professionally

Following this lab activity, how would you rate your comfort with soldering a lap joint?

☐ I couldn’t do it again.

☐ I know enough to explain what I did.

☐ I know enough to replicate what I did.

☐ I know enough to replicate what I did using the appropriate vocabulary

☐ I’m now an expert and can solder lap joints perfectly on the first try

Write about three things that you learned:

I learned that tinning is crucial for a good mechanical connection when soldering

I learned to solder on the bottom of PCB’s rather than the top because there are times when you might not be able to solder from the top.

Don’t paint the solder

Write about two things that made you curious or confused:

I was curious how the solder just wicks straight to the component

I was wondering if some of the helping hands have softer clips because the alligator clips destroyed the wire

Write about one most important thing you learned or should do with what you learned:

You want to heat the wire rather than the solder, the solder will flow where the heat is.

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