Lab #4 Help Document
This help document will be structured as a walk-through of the lab. We will include instructions about how to
write the report throughout this help document.
This lab will be completed in room 260 CTB (door-code 60197).
The bulk of the work for this lab will consist of observations and recordings of components. The order in which
you observe the parts is not important, but please record them in the order that the lab document calls them
in. This will make grading your reports easier for us and it will require less time to do allowing us to get them
back to you faster.
You will need to partner up for this lab in groups of two. Alternate who records data and who conducts the
observations. It is okay for you to submit the same data, but not the same exact report as each individual will
need to draw his or her own conclusions and analyze the data. Only 6 groups will be able to use the
microscopes at any given time. The sections for the 1 ohm power resistor, linear trimpot, and rotary trimpot do
not require the use of microscopes, so if you don't have access to a microscope at the moment, try to work on
those sections. Use the dial calipers for measuring those components when possible.
This lab will require the use of the following pieces of equipment:
National Stereo Zoom Microscope
Stereo Zoom Microscope Calibration slides
Magnifying glasses
Dial Calipers
Samples:
1) a lengthwise section of a 1.0 MΩ carbon film or metal film, ¼-Watt resistor
2) two carbon or metal film resistors which have had the enamel/epoxy paint scraped off
3) a lengthwise section of a 47 Ω carbon composition 1-Watt resistor
4) a 1 Ω wirewound power resistor which has had the enamel/epoxy paint sandblasted off
5) chip resistors, various sizes, mounted on small circuit boards
6) a sectioned linear trimpot, unmounted
7) a sectioned rotary trimpot, unmounted
8) a sectioned SOIC network resistor
9) the same SOIC network resistor mounted on a PCB with the enamel/epoxy paint sandblasted off.
1. First go to the class website and study the pictures there for this lab. Correlate them with the material
covered in class and in the text. Be prepared to find and study these structures under the microscope or
magnifying glass.
Here is a link to the class web page:
http://it318.groups.et.byu.net/
To access these images, click on Labs located on the left side of the screen. Then click on the link labeled
pictures for lab 4 under the aids column.
Things to include in lab report: State that you looked at these images. Record any impressions you have. If
nothing in particular strikes you, then only state that you looked at these images.
2. Observe in detail the construction of the carbon/metal film resistor (samples #1 and #2). Note and
describe how the end caps are joined to the mandrel, and how the leads are joined to the end caps. Measure
the thickness of the carbon/metal film; was it applied by thin or thick film processes? Measure the width of
the helix path on each resistor and compare them. Measure the width of the laser ablation path on each and
compare them. Which resistor would you expect to have the highest value, and why?
Before you can begin observations, you will need to set up the microscope.
Setting up the microscope
To do so, first log onto one of the computers at your workstation using your IT log-in. Next, click on the desktop
icon that says, “Motic Images Plus 2.0 ML”. After it loads, click on the “Capture” button with the camera on it at
the top of the screen. This will open the Motic Live Imaging Module which will allow you to view objects that
you place on the microscope.
Now click on the 3rd tab down on the left side of the screen with the gear and wrench on it. Select the grid
option. This puts a grid on the screen which you can use to make general measurements of the features you
are observing. To change the size of each grid square, click the settings button. The base unit for the grid size is
micrometers (abbreviated um on the screen).
NOTE: Do NOT use the values specified in the Grid Setting dialogue box for gauging the grid size. They do not
represent the size of the grid squares. To determine the size of a grid square, you first need to set the
microscope to 1x magnification. Then, use a calibration dot under the scope and determine how many grid
squares it is tall. Divide the diameter of the dot by that number of squares and you will have an effective
estimate for the length and width of a grid square. In most cases, a grid square is about 800um x 800um
(micrometers). If you adjust the magnification of the microscope, remember to adjust the grid size accordingly.
For example:
1x = 800x800
2x = 400x400
3x = 267x267
4x = 200x200
Unless otherwise specified by the lab, it is okay to specify your measurements using micrometers. Because of
the limitations of the lab equipment and the possibility that people will measure different areas of the same
feature, it is okay if the measurements are not exact. Just report what you measure and you will get full credit
for that measurement.
Now you need to set up the actual microscope. First, turn on the switch that is labeled “Main”. This is the main
power of the scope and none of the other switches will work if it is not on. Also, you won't see anything on
your computer screen if this is not on.
The two switches on the right side turn on and off the lower and upper lighting of the microscope.
The left button turns on the overhead light, and the right button turns on the lower light.
You can use whichever setting or combination you prefer to get the desired result, but we recommend using the
overhead light only. The lower light just shines light up into the camera and obscures the image. To adjust the
focus of the microscope, turn the larger of the two sets of knobs.
The larger knobs control focus. The smaller knobs are used to adjust image magnification (between 1x and 4x)
and have no effect on the clarity or focus of the image. Set the small knobs at 1x as a default and remember to
adjust the estimated grid based on the magnification you have set. Also, there is a silver/chrome rod on the
back of the microscope that looks like a large nail sticking out of the back. Make sure that this is pulled out of
the scope as far as it will go. If it is pushed in, the camera on the microscope will be covered and you will not
see anything on your screen. You can check this by looking into the microscope. If you can see something with
your left eye, but the right eye is blacked out, then the camera is on and you should be able to see something
on your screen. If you can see something with your right eye, the rod is pushed in and you will need to pull it
until it is in the out position.
To view an object, place it under the lens of the microscope and move it until you can see it on the screen.
Adjust the focus and lighting as is necessary to obtain a clear image. The optimum image focus may be above
or below the range of the focus knobs. To resolve this, adjust the height of the entire microscope using the
knob on the back. Be sure to screw it back tightly so that the microscope doesn't move around when you are
making your observations.
Procedure
For part 2 of the lab, select the sample of the lengthwise section of a 1.0 MΩ carbon film resistor (sample 1)
and the sample of the two carbon or metal film resistors which have had the enamel/epoxy paint scraped off
(sample 2). These samples comprise a set and there is only one set, so only one group will be able to use it at a
time.
Tip: Use just the over-head light for this sample if you want a clear view. If you want to save yourself some time
making adjustments, look first at the 1 M ohm carbon film resistor impregnated in the black disk. After getting
it focused and after making the necessary observations, simply flip it over and place one of the resistors from
sample 2 on its back.
This should give you a clear image of sample 2 without having to refocus things. Along this same train of
thought, if you can get sample 3 next, do so because it is the same height as sample 2 and so will not require
much adjustment. Sample 8 is slightly shorter than 1 or 2, so it will require a little more adjusting.
Answer the following questions and make the following measurements:
(note that when looking at sample 1, that really dark line down the middle of it is NOT a part of the component.
This sample broke in half when it was cut and that black line is the break.)
Note and describe how the end caps are joined to the mandrel, and how the leads are joined to the end caps.
Examples: bonded, soldered, press fit, etc.
Measure the thickness of the carbon/metal film. This is the outer coating on the mandrel that the paint is
applied over. It is dark or gray/silver.
Was it applied by thin or thick film processes? Is the film thick or thin relative to the part?
Measure the width of the helix path on each resistor and compare them. This is the thickness of each coil of the
helix. For sample 1, the helix path will be between the slight indentations along the top and bottom of the
mandrel. Measure the distance between two of these indentations. Remember to measure this for both resistor
samples (sample 1 and sample 2) and offer a comparison.
Measure the width of the laser ablation path on each and compare them. For sample 1, this is the width of the
indentations described above. Each indentation is part of the laser ablation path that wraps around the
mandrel.
Which resistor would you expect to have the highest value, and why? Hint: think about the number of coils on
each resistor and their thickness.
Things to include in lab report: All answers to the above questions. If the question asks for a measurement,
give a number and the units. After answering the questions, include anything else you want to mention for this
section such as observations or analysis. If you don't want to include anything else, that is fine.
3. Observe and describe in detail the construction of the carbon composition resistor (sample #3). Speculate
on the manufacturing steps required to produce it. Measure the thickness of the epoxy coating; is it thinner
or thicker than you expected, or is it about what you would have expected? See if you can observe the
different particles in the carbon composition (ceramic and carbon); if so, describe their relative proportions
and sizes.
For this part of the lab, select the sample of the lengthwise section of a 47 Ω carbon composition 1-Watt
resistor (sample 3). There is only one sample of this, so only one group will be able to use it at a time.
Tip: Use just the over-head light for this sample if you want a clear view. If you want to save yourself some time
making adjustments, after getting this sample focused and after making the necessary observations, try to get
samples 1 and 2 next because they are (or rather can be used at) the same height as sample 2 and so will not
require much adjustment to the microscope. Sample 8 is slightly shorter than 1, 2, or 3, so it won't quite work
the same way.
Answer the following questions and make the following measurements:
Observe and describe in detail the construction of the carbon composition resistor. Basically, describe the
structure of the resistor. X part is attached to Y part and is made of Z substance.
Speculate on the manufacturing steps required to produce it. Basically say something like this: “This part looks
like it was made by x process. This other part was then attached with y process and the assembly was then
coated with z material.
Measure the thickness of the epoxy coating. Is it thinner or thicker than you expected, or is it about what you
would have expected? This is the brown coating around the black center. Be sure to explain why it is or isn’t
thicker than what you would have expected. Your explanation doesn’t have to be right, you just need to have
one that makes sense.
See if you can observe the different particles in the carbon composition (ceramic and carbon); if so, describe
their relative proportions and sizes. The ceramic particles are those really small brownish specs. Relative size
means you don't need means you don't need an exact measurement. They're x times bigger or smaller than the
carbon ones will suffice. If you can’t see them, state that you couldn’t see them.
Things to include in lab report: All answers to the above questions. If the question asks for a measurement,
give a number and the units. After answering the questions, include anything else you want to mention for this
section such as observations or analysis. If you don't want to include anything else, that is fine.
4. Observe and describe in detail the construction of the wirewound power resistor (sample #4). How are the
wire resistance elements joined to the end caps? How many resistance elements are there? What is the
material the mandrel is made of? What is the diameter of the wire used for the resistance elements?
For this part of the lab, select the sample of the 1 Ω wirewound power resistor which has had the
enamel/epoxy paint sandblasted off (sample 4). There is only one sample of this, so only one group will be able
to use it at a time.
Tip: This thing is big, so you won't really need the microscope to look at it. Some features are small enough
that using a magnifying glass would be helpful though. Use the dial calipers for any measurements, just be sure
to specify the units as the calipers measure in inches not micrometers.
Answer the following questions and make the following measurements:
Observe and describe in detail the construction of the wirewound power resistor. Basically, describe the
structure of the resistor. X part is attached to Y part and is made of Z substance.
How are the wire resistance elements joined to the end caps? Examples: bonded, soldered, press fit, etc.
How many resistance elements are there? This is the number of wires going around the mandrel, not the
number of coils in the helix.
What is the material the mandrel is made of? I think it’s made out of aluminum oxide (a.k.a. alumina) based on
my own research.
What is the diameter of the wire used for the resistance elements? Find by measurement using the microscope
or dial calipers.
Things to include in lab report: All answers to the above questions. If the question asks for a measurement,
give a number and the units. After answering the questions, include anything else you want to mention for this
section such as observations or analysis. If you don't want to include anything else, that is fine.
5. Observe and describe in detail one of the chip components (it could be a chip resistor or capacitor – it’s
very hard to tell the difference externally). Give its dimensions and then its industry designation as to the size
of the component. For example, a chip resistor that measures 20 x 10 mils would be an 0201.
For this part of the lab, select the sample of the 1 chip resistors, various sizes, mounted on small circuit boards
(sample 5). There are two samples of this, so two groups will be able to use them at the same time.
Tip: Bigger components are easier to work with and the lab does not require a specific size.
Tip: These could be measured using the dial calipers to avoid having to do a unit conversion between inches
and um. A mil is equal to 0.001 inches.
Answer the following questions and make the following measurements:
Observe and describe in detail one of the chip components (it could be a chip resistor or capacitor – it’s very
hard to tell the difference externally). Can include shape, size, notable features, what it makes you think of, etc.
Give its dimensions and then its industry designation based on the size of the component. For example, a chip
resistor that measures 20 x 10 mils would be an 0201. To do this, you may need to convert between um and
mils if you made the measurement with the microscope. 25.4 um = 1 mil. If you can't see the grid because it is
black, go to the grid settings and change the color to white. The calipers measure in inches and 1 inch = 1,000
mils. To put the dimensions in in industry designation, here is an example chart:
2milx1mil
→ 002001
20x10
→ 0201
200x100
→ 2010
2000x1000
→ 200100
Things to include in lab report: All answers to the above questions. If the question asks for a measurement,
give a number and the units. After answering the questions, include anything else you want to mention for this
section such as observations or analysis. If you don't want to include anything else, that is fine.
6. Observe and describe in detail the construction of the sectioned linear trimpot (sample #6). Describe the
path normally taken by current from one of the end terminals to the wiper terminal. Speculate on the
process required to manufacture this part. What is the material the resistive substrate is made of? What do
you expect the resistive element to be made of?
For this part of the lab, select the sample of the a sectioned linear trimpot (sample 6) . There is only one
sample of this, so only one group will be able to use it at a time.
Tip: You won't need to microscope for this part, so do it later if you have a microscope right now. If you don't
have a microscope, do this part now if the sample is available.
Answer the following questions and make the following measurements:
Observe and describe in detail the construction of the sectioned linear trimpot. Basically, describe the structure
of the trimpot. X part is attached to Y part and is made of Z substance.
Describe the path normally taken by current from one of the end terminals to the wiper terminal. Electricity
looks like it goes in which side, through what, and out of what.
Speculate on the process required to manufacture this part. Basically say something like this: “This part looks
like it was made by x process. This other part was then attached with y process and the assembly was then
coated with z material.
What is the material the resistive substrate is made of? The resistive substrate is the white block that the black
strip is on. It's looks like it’s made of either alumina or plastic.
What do you expect the resistive element to be made of? The resistive element is that small black strip under
the yellow wiper. I think it’s made of carbon-rubidium composite.
Things to include in lab report: All answers to the above questions. If the question asks for a measurement,
give a number and the units. After answering the questions, include anything else you want to mention for this
section such as observations or analysis. If you don't want to include anything else, that is fine.
7. Repeat step 5 for the sectioned rotary trimpot (sample #7). Based on your observations for these two
trimpots, describe what causes noise when worn pots are adjusted.
For this part of the lab, select the sample of the sectioned rotary trimpot (sample 7). There is only one sample
of this, so only one group will be able to use it at a time.
Tip: You won't need to microscope for this part, so do it later if you have a microscope right now. If you don't
have a microscope, do this part now if the sample is available.
Answer the following questions and make the following measurements:
Repeat step 6 for the sectioned rotary trimpot. This means answer all of the questions from part 6 above for
this rotary trimpot.
Based on your observations for these two trimpots, describe what causes noise when worn pots are adjusted.
Hint: these two pots adjust resistance by sliding one surface over another. What happens when surfaces rub
against each other repeatedly over time?
Things to include in lab report: All answers to the above questions. If the question asks for a measurement,
give a number and the units. After answering the questions, include anything else you want to mention for this
section such as observations or analysis. If you don't want to include anything else, that is fine.
8. Observe and describe in detail the construction of the sectioned and sandblasted SOIC network resistor.
Note and describe how the leads are joined to the substrate. Measure the thickness of the resistance
element and compare it to the same for the carbon/metal film resistors.
For this part of the lab, select the samples of sectioned SOIC network resistor and the same SOIC network
resistor mounted on a PCB with the enamel/epoxy paint sandblasted off (samples 8 and 9). There is only one
sample of this, so only one group will be able to use it at a time.
Tip: Adjust your grid color if you can't see the grid lines easily.
Answer the following questions and make the following measurements:
Observe and describe in detail the construction of the sectioned and sandblasted SOIC network resistor.
Basically, describe the structure of the SOIC. X part is attached to Y part and is made of Z substance.
Note and describe how the leads are joined to the substrate. Examples: bonded, soldered, press fit, etc.
Measure the thickness of the resistance element and compare it to the same for the carbon/metal film
resistors. You will need to look at the cross section (sample 8) for this. The resistance element is the thin
metallic dashed line on top of the white block.
Measure the width of the laser ablation path and compare it to the same for the carbon/metal film resistors.
Also note any other things you observed of particular interest. You can use either sample for this. The width of
the laser ablation path is the distance between the metallic surfaces. It looks greenish-white.
Things to include in lab report: All answers to the above questions. If the question asks for a measurement,
give a number and the units. After answering the questions, include anything else you want to mention for this
section such as observations or analysis. If you don't want to include anything else, that is fine.
Summary/Conclusion
For the lab report summary/conclusion, answer or analyze the following:
-Compare the carbon/metal film resistors and the carbon composition resistor.
-What evidence did you see of the following characteristics: 1) capacity to withstand current surges;
2) tolerance; 3) cost.
-If a wirewound resistor were made as small as the carbon/metal film resistors, how would you expect it to
compare with these resistors in each of these previous characteristics?
-Based on your observations of the construction of the trimpots, speculate on their cost relative to the fixed
resistors. How many adjustment cycles do you expect they would withstand before noise became a problem?
-Include anything else you feel is worthy of mention.
Things to include in lab report: All answers to the above questions.