Pre-announcement: I am a China fan, and my English is not very good. All English is supported by the translator. I am deeply sorry if u can't understand and have any ambiguity.
Disclaimer:
1: This is a geek production, and the final test conclusion after our production is that it can hardly be used as a standard resistor and its performance is poor. Unless you use a special packaging method: airtight packaging.
2: Its production process maybe full of environmental bad factors. This amateur production is not for environmentalists. Please watch it according to your local cultural habits, legal provisions and administrative system.
A long time ago, I heard the myth of PIO capacitor and Allen Bradley (this is often simply called AB in China) carbon composition resistor. They are not the most perfect representatives of audio fidelity, but they have occupied a considerable market in historical audio manufacturing based on their cheapness and universality, so that it has become a fashion and habit. I have some PIO and CC on hand as samples, but they still can't satisfy me.
1: The CC produced later used the sintering process, just like clay pencil lead. After mixing graphite raw materials and clay, it was pressed and molded and sent to a high-temperature furnace for graphitization, forming a solid whole. This process typically has ideal resistance performance in CC-hard structure, low water absorption, low voltage coefficient (in CC family series), good durability and drift rate. But the question is, what is the purpose of this resistor? I want him to give me a special distortion. If you do it well, where will my distortion go?
2: Since the later CC is invariably a sintering process, I don't know enough about the most traditional organic bonding process. What I want to do is: Can I build a process different from the normal CC and form a resistor, which can not only help me realize the fun of "home DIY", but also be used in some unique and strange places? I don't want EE to criticize me here. "This resistor is too bad, it doesn't apply to audio." I know this clearly. I need it, I'll do it-that's my purpose. Fortunately, based on the knowledge given by various network platforms and enthusiastic netizens, I successfully manufactured a "junk" resistor-"gold" carbon resistor. The following is the production process.
Disclaimer:
1: This is a geek production, and the final test conclusion after our production is that it can hardly be used as a standard resistor and its performance is poor. Unless you use a special packaging method: airtight packaging.
2: Its production process maybe full of environmental bad factors. This amateur production is not for environmentalists. Please watch it according to your local cultural habits, legal provisions and administrative system.
A long time ago, I heard the myth of PIO capacitor and Allen Bradley (this is often simply called AB in China) carbon composition resistor. They are not the most perfect representatives of audio fidelity, but they have occupied a considerable market in historical audio manufacturing based on their cheapness and universality, so that it has become a fashion and habit. I have some PIO and CC on hand as samples, but they still can't satisfy me.
1: The CC produced later used the sintering process, just like clay pencil lead. After mixing graphite raw materials and clay, it was pressed and molded and sent to a high-temperature furnace for graphitization, forming a solid whole. This process typically has ideal resistance performance in CC-hard structure, low water absorption, low voltage coefficient (in CC family series), good durability and drift rate. But the question is, what is the purpose of this resistor? I want him to give me a special distortion. If you do it well, where will my distortion go?
2: Since the later CC is invariably a sintering process, I don't know enough about the most traditional organic bonding process. What I want to do is: Can I build a process different from the normal CC and form a resistor, which can not only help me realize the fun of "home DIY", but also be used in some unique and strange places? I don't want EE to criticize me here. "This resistor is too bad, it doesn't apply to audio." I know this clearly. I need it, I'll do it-that's my purpose. Fortunately, based on the knowledge given by various network platforms and enthusiastic netizens, I successfully manufactured a "junk" resistor-"gold" carbon resistor. The following is the production process.
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Construction of carbon conduction mechanism. Simply put, it is how to fix a group of carbon together and make it conductive. Obviously, I don't have the high-end equipment like muffle furnace, and it is impossible to use clay for firing. I can only hope to use the carbon structure solidified by organic substances.
Based on very primitive behavior, amorphous carbon used for conducting electricity is not a purchased finished product (although their price is not expensive in China, the average price of conducting acetylene black industrial products is only a few dollars per kilogram), it is obtained from the lamp black baked on a vegetable oil lamp-I successfully proved that this kind of carbon black is indeed conductive through the lamp black and interdigital aluminum electrodes that I took over on paper in high school. They are not graphite, but amorphous carbon. Blacker, looser structure, and several times higher resistivity than graphite.
Another key problem is to choose a suitable curing material, which can not only firmly fix the amorphous carbon together, but also make the carbon contact with each other to form a conductive path. I first used 502 glue (ethyl cyanoacrylate quick glue) on the paper with lamp black to cure them. The effect was average, with tens of thousands of ppm voltage coefficient (VCR) and unimaginable hysteresis changes in the resistance than various modern industrial products, and it was difficult to accumulate enough lamp black on the paper, which made it difficult to reduce the resistance value. At one time, I could only make the resistance of simple electrode structure from hundred-kilos of ohms to 1~2mega of ohms, but I couldn't make their resistance smaller. This experiment was first carried out around 2018 ~ 2019, and later a relatively complete reproduction experiment was carried out around October 2024. I described it completely in the Chinese website. See the following links for details:
DIY Carbon resistor(CHN,中文)
The manufactured resistance sample is encapsulated by epoxy resin and sprayed with black paint.
Carbon in paper
Because ethyl cyanoacrylate glue has water absorption characteristics and poor temperature resistance, I did some experiments in the later stage to mix amorphous carbon powder with epoxy resin, hoping to get a conductive plastic with good fixing performance for carbon powder, but unfortunately the experiment failed-even if I increased the weight ratio of carbon powder to epoxy resin to 1:1 or even higher, epoxy resin could still effectively separate amorphous carbon powder and insulate the whole resin. I have done a lot of experiments, but I can't measure the effective conductive resistance. These experiments were carried out from October to November, 2024. At the last time, I even made a little thing like the carbon core of AB carbon resistor-it was mixed with 60% carbon and 40% epoxy resin, and it was almost impossible for me to get into more proportion before it solidified because it was sticky like plasticine played by children. Even so, however, it still not conductive.
It looks like ab carbon resistor with its shell removed, but it is not conductive. When I put it on the gas stove and decomposed the epoxy resin into carbon with a torch, it began to conduct electricity, but its mechanical strength was gone.
Based on very primitive behavior, amorphous carbon used for conducting electricity is not a purchased finished product (although their price is not expensive in China, the average price of conducting acetylene black industrial products is only a few dollars per kilogram), it is obtained from the lamp black baked on a vegetable oil lamp-I successfully proved that this kind of carbon black is indeed conductive through the lamp black and interdigital aluminum electrodes that I took over on paper in high school. They are not graphite, but amorphous carbon. Blacker, looser structure, and several times higher resistivity than graphite.
Another key problem is to choose a suitable curing material, which can not only firmly fix the amorphous carbon together, but also make the carbon contact with each other to form a conductive path. I first used 502 glue (ethyl cyanoacrylate quick glue) on the paper with lamp black to cure them. The effect was average, with tens of thousands of ppm voltage coefficient (VCR) and unimaginable hysteresis changes in the resistance than various modern industrial products, and it was difficult to accumulate enough lamp black on the paper, which made it difficult to reduce the resistance value. At one time, I could only make the resistance of simple electrode structure from hundred-kilos of ohms to 1~2mega of ohms, but I couldn't make their resistance smaller. This experiment was first carried out around 2018 ~ 2019, and later a relatively complete reproduction experiment was carried out around October 2024. I described it completely in the Chinese website. See the following links for details:
DIY Carbon resistor(CHN,中文)
The manufactured resistance sample is encapsulated by epoxy resin and sprayed with black paint.
Carbon in paper
Because ethyl cyanoacrylate glue has water absorption characteristics and poor temperature resistance, I did some experiments in the later stage to mix amorphous carbon powder with epoxy resin, hoping to get a conductive plastic with good fixing performance for carbon powder, but unfortunately the experiment failed-even if I increased the weight ratio of carbon powder to epoxy resin to 1:1 or even higher, epoxy resin could still effectively separate amorphous carbon powder and insulate the whole resin. I have done a lot of experiments, but I can't measure the effective conductive resistance. These experiments were carried out from October to November, 2024. At the last time, I even made a little thing like the carbon core of AB carbon resistor-it was mixed with 60% carbon and 40% epoxy resin, and it was almost impossible for me to get into more proportion before it solidified because it was sticky like plasticine played by children. Even so, however, it still not conductive.
It looks like ab carbon resistor with its shell removed, but it is not conductive. When I put it on the gas stove and decomposed the epoxy resin into carbon with a torch, it began to conduct electricity, but its mechanical strength was gone.
Until a few days ago, when I searched for carbon resistors aimlessly, I found a possible and very simple carbon paste formula: adding PVA and PVAC with graphite, which may sound a little more complicated than the above method, but the latter two just constitute a kind of glue commonly used for children's sticky paper-handmade white latex, and fortunately I have these materials left. In theory, using this formula will have great success, because PVA is a solvent. But PVAC only accounts for a small part of it. When the solvent volatilizes, only a small part of the substance is used to fix carbon, which is so little that it makes the interconnection of carbon extremely possible. Based on this rough carbon slurry formula, I tried an experiment: success. This is today's theme: the first step in manufacturing "gold" carbon resistor.
1: Make a skeleton. We choose FR4 as the base material, because the mechanical strength is relatively high and it is easier to process, but be careful of the dust during processing! Please wear a mask to operate. (Based on a well-known global public health incident, I still have enough masks), and this skeleton comes standard with two tin-plated copper pins.
2: Making electrodes. The electrode is made of small thin copper tape, and then it is soldered and tinned with lead solder-lead-free solder will lead to the faster damage of the adhesive on the back of the copper tape, so unfortunately this resistor is not RoHS, and the finished skeleton is not in direct contact with the electrode, but transited through the bundled thin wires, which can reduce the damage caused by stress to this poor resistor.
The Liquid in tube is alcohol，Which used for cleaning the rosin
3: Prepare carbon paste, and use hand-made white latex to mix the lamp black collected from the oil lamp (I think the fineness of the lamp black and the crystallinity of graphite particles in it may affect the resistance noise, so maybe olive oil and coconut oil have different sounds? Haha, only God knows. I used rapeseed oil anyway. ), the principle of configuration is to mix a little thinner than plasticine but a little thicker than mud. And then coated on the resistor skeleton.
4: Dry. I may have made a mistake in this step: I used infrared baking in a hurry, and as a result, the surface layer dried too fast, which led to cracking. Maybe it wouldn't crack if it was slower, but I'm not sure whether this idea is correct. When testing its resistance value with a multimeter while drying, it will gradually decay from 22kΩ to 3.46kΩ (this is the result of my work, and 3.46kΩ is probably a stable value after thorough baking). The gradually decaying resistance means that the solvent inside is evaporating.
5: Apply 502 glue for curing. Because the dried PVC is an elastic colloid, the dried carbon is not too hard, and the water resistance is very poor. When we apply 502 on the surface, the high-permeability 502 glue will penetrate into the gap and form a more solid plastic structure.
6: Packaging: use transparent epoxy resin, mix silica reinforcement and gold powder dyeing (definitely not Ture gold , because 100g is only RMB three yuan. It's just a special surface-modified micro-powder that can emit golden flash, and it's not conductive.), and then quickly put the heated resistor core into the mold for packaging (the purpose of baking is to drive away moisture, because it is easy to absorb moisture even if it is coated with 502). The shell is made of paper tube, and vaseline is coated inside, so the epoxy resin will not stick to the paper tube.
7: demoulding: after the epoxy resin is dried, the paper shell is torn off, and the complete resistor can be obtained.
1: Make a skeleton. We choose FR4 as the base material, because the mechanical strength is relatively high and it is easier to process, but be careful of the dust during processing! Please wear a mask to operate. (Based on a well-known global public health incident, I still have enough masks), and this skeleton comes standard with two tin-plated copper pins.
2: Making electrodes. The electrode is made of small thin copper tape, and then it is soldered and tinned with lead solder-lead-free solder will lead to the faster damage of the adhesive on the back of the copper tape, so unfortunately this resistor is not RoHS, and the finished skeleton is not in direct contact with the electrode, but transited through the bundled thin wires, which can reduce the damage caused by stress to this poor resistor.
The Liquid in tube is alcohol，Which used for cleaning the rosin
3: Prepare carbon paste, and use hand-made white latex to mix the lamp black collected from the oil lamp (I think the fineness of the lamp black and the crystallinity of graphite particles in it may affect the resistance noise, so maybe olive oil and coconut oil have different sounds? Haha, only God knows. I used rapeseed oil anyway. ), the principle of configuration is to mix a little thinner than plasticine but a little thicker than mud. And then coated on the resistor skeleton.
4: Dry. I may have made a mistake in this step: I used infrared baking in a hurry, and as a result, the surface layer dried too fast, which led to cracking. Maybe it wouldn't crack if it was slower, but I'm not sure whether this idea is correct. When testing its resistance value with a multimeter while drying, it will gradually decay from 22kΩ to 3.46kΩ (this is the result of my work, and 3.46kΩ is probably a stable value after thorough baking). The gradually decaying resistance means that the solvent inside is evaporating.
5: Apply 502 glue for curing. Because the dried PVC is an elastic colloid, the dried carbon is not too hard, and the water resistance is very poor. When we apply 502 on the surface, the high-permeability 502 glue will penetrate into the gap and form a more solid plastic structure.
6: Packaging: use transparent epoxy resin, mix silica reinforcement and gold powder dyeing (definitely not Ture gold , because 100g is only RMB three yuan. It's just a special surface-modified micro-powder that can emit golden flash, and it's not conductive.), and then quickly put the heated resistor core into the mold for packaging (the purpose of baking is to drive away moisture, because it is easy to absorb moisture even if it is coated with 502). The shell is made of paper tube, and vaseline is coated inside, so the epoxy resin will not stick to the paper tube.
7: demoulding: after the epoxy resin is dried, the paper shell is torn off, and the complete resistor can be obtained.
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Other supplementary statements:
1. Resistance value. The resistance value of the whole resistor changed repeatedly by 100% or even more before the epoxy resin was cured, and it stabilized at about 1302 Ω after the epoxy resin was cured-but I'm not sure that this resistance value has been stable all the time, so I need to test the resistance value and make a test report after storing this resistor for a longer time.
2: Size and power. The size of the package is about D12*L40mm, which is only the plastic part of epoxy resin and not included in the pin. The power is about 0.2W. Based on this resistance has high thermal resistance and low tempture work of organic materials inside.
3: Voltage coefficient. Different from the voltage coefficient of the general resistor in ppm level, the voltage coefficient of this resistor is very outrageous-it can reach thousands of ppm or more, which can bring extremely rich coloring to your audio (if you really need these coloring).
4: Noise, you can hear the noise directly by connecting a 1.5 volt battery in series through this resistor and headphones.
If you really want to use this resistor, then our suggestion is to use it on the "gate resistor" of JFET or OPA-these two places have wide requirements for resistor accuracy and are sensitive to audio.
Hope u good luck
😃
1. Resistance value. The resistance value of the whole resistor changed repeatedly by 100% or even more before the epoxy resin was cured, and it stabilized at about 1302 Ω after the epoxy resin was cured-but I'm not sure that this resistance value has been stable all the time, so I need to test the resistance value and make a test report after storing this resistor for a longer time.
2: Size and power. The size of the package is about D12*L40mm, which is only the plastic part of epoxy resin and not included in the pin. The power is about 0.2W. Based on this resistance has high thermal resistance and low tempture work of organic materials inside.
3: Voltage coefficient. Different from the voltage coefficient of the general resistor in ppm level, the voltage coefficient of this resistor is very outrageous-it can reach thousands of ppm or more, which can bring extremely rich coloring to your audio (if you really need these coloring).
4: Noise, you can hear the noise directly by connecting a 1.5 volt battery in series through this resistor and headphones.
If you really want to use this resistor, then our suggestion is to use it on the "gate resistor" of JFET or OPA-these two places have wide requirements for resistor accuracy and are sensitive to audio.
Hope u good luck
😃
Fascinating experiments... I didn't imagine it would be easy to make such a device oneself, but its great to put in the effort and see what can be achieved.
I have tried myself to build resistors from scratch, mainly using low-temp processes, but I have had little success. I sometimes managed to get a half-decent result (reasonably stable values, acceptable tempco and tolerable voltage coefficient), but it was hit and miss with lots of rejects and a result widely inferior compared to industrial types.
Basically, this kind of construction is carbon composition in one form or another, and it comes with its inherent weaknesses. I have tried to replace the carbon with other materials, like tin oxide, with varied results.
I have also tried to coat a ceramic substrate using a chemical solution to leave a resistive film, but it was also hit and miss.
Finally, I used the plasma generated by a Tesla coil to "bake" a quasi-insulating mix of an organic binder and carbon powder, to make it resistive, again with semi-random results.
Tomorrow, I'll try to post pictures of my attempts.
In the end I managed to make a good one that I used in my ion-chamber project, but that was a lot of work for a meagre result.
Without vacuum technology, high temperature ovens, ion sputtering equipments etc., it is difficult to arrive at a usable result.
One option looks interesting: I remember that in a vintage DIY radio dating from ~1925, I saw a resistor made by "Le véritable alter" or a similar manufacturer which consisted in a glass filament (certainly resistive) enclosed in an evacuated glass vessel.
The filament looked perfectly transparent, but it was obviously doped with something that made it slightly conducting.
The thing must still be somewhere in my attic, but locating it would be difficult.
This technology could more easily be duplicated with DIY means: glass work is possible at reasonable temperatures, and once finished it could be very stable and durable; one just needs to (re)find the glass doping formula
Basically, this kind of construction is carbon composition in one form or another, and it comes with its inherent weaknesses. I have tried to replace the carbon with other materials, like tin oxide, with varied results.
I have also tried to coat a ceramic substrate using a chemical solution to leave a resistive film, but it was also hit and miss.
Finally, I used the plasma generated by a Tesla coil to "bake" a quasi-insulating mix of an organic binder and carbon powder, to make it resistive, again with semi-random results.
Tomorrow, I'll try to post pictures of my attempts.
In the end I managed to make a good one that I used in my ion-chamber project, but that was a lot of work for a meagre result.
Without vacuum technology, high temperature ovens, ion sputtering equipments etc., it is difficult to arrive at a usable result.
One option looks interesting: I remember that in a vintage DIY radio dating from ~1925, I saw a resistor made by "Le véritable alter" or a similar manufacturer which consisted in a glass filament (certainly resistive) enclosed in an evacuated glass vessel.
The filament looked perfectly transparent, but it was obviously doped with something that made it slightly conducting.
The thing must still be somewhere in my attic, but locating it would be difficult.
This technology could more easily be duplicated with DIY means: glass work is possible at reasonable temperatures, and once finished it could be very stable and durable; one just needs to (re)find the glass doping formula
Humm, in fact, what I really want to do is an organic carbon resistor with high stability. There are quite a few reasons for this resistor to withdraw from the industrial production of fixed resistors very early.
Organic carbon resistor has strong hygroscopicity. If you don't make airtight packaging such as glass packaging and ceramic packaging, the stability of the resistor is basically poor-of course, in some places, high stability is not needed, such as the self-biased gate resistance of the cathode of the electron tube, which can generally tolerate any resistance within 500 kΩ-as long as it is not too small, the load working point of the previous electron tube becomes too severe to damage the health of the electron tube. For some JFET, this value can reach 1GΩ.
Organic mixed carbon resistor is completely different from the later carbon film resistor. The carbon film resistor is a crystallized graphite layer (by vacuum reduction deposition process), which has good conductivity, resistance stability and low noise. However, this resistor is just the opposite-unstable amorphous carbon and unstable organic substances form a mess, and you have no idea how many carbon particles are in direct contact with each other and the conductive areas that are separated by insulating substances and need to be tunneled by high voltage. You can't even control the final resistance value-but that's the charm. There is a wild beauty, a beauty in which carbon ink for painting and calligraphy was coated on paper strips in the early days of radio and then packaged in glass tubes as grid leakage resistor. When it is connected with a modern industrial precision resistor with the same resistance value, its nature can be completely exposed-this is an ancient traditional taste, just like the bad characteristics I hope to get from PIO and AB resistors. This is not a fidelity project, and it doesn't need to be accurate or good. I can draw an abstract landscape painting when use ink made of amorphous carbon, or I can make it into a resistor to put it down on my audio equipment. They are all the realization of personal abstraction.
If it is obviously not a cost-effective choice for individuals to make industrial-grade resistors, I suggest buying finished products-at least there are enough of these finished products available in China, and the price is not expensive, and the high-resistance resistors range from 40 cents to 10 dollars. Of course, the cheap price is poor performance (for example, high-resistance resistors also have absorption effect, and cheap high-resistance resistors may not use some precious metal oxides, resulting in their large temperature drift). However, compared with those "self-achievement products" of DIY, they are still very acceptable (note that there are many "abstractions" things in the electronic market in China, so don't buy them blindly).
Organic carbon resistor has strong hygroscopicity. If you don't make airtight packaging such as glass packaging and ceramic packaging, the stability of the resistor is basically poor-of course, in some places, high stability is not needed, such as the self-biased gate resistance of the cathode of the electron tube, which can generally tolerate any resistance within 500 kΩ-as long as it is not too small, the load working point of the previous electron tube becomes too severe to damage the health of the electron tube. For some JFET, this value can reach 1GΩ.
Organic mixed carbon resistor is completely different from the later carbon film resistor. The carbon film resistor is a crystallized graphite layer (by vacuum reduction deposition process), which has good conductivity, resistance stability and low noise. However, this resistor is just the opposite-unstable amorphous carbon and unstable organic substances form a mess, and you have no idea how many carbon particles are in direct contact with each other and the conductive areas that are separated by insulating substances and need to be tunneled by high voltage. You can't even control the final resistance value-but that's the charm. There is a wild beauty, a beauty in which carbon ink for painting and calligraphy was coated on paper strips in the early days of radio and then packaged in glass tubes as grid leakage resistor. When it is connected with a modern industrial precision resistor with the same resistance value, its nature can be completely exposed-this is an ancient traditional taste, just like the bad characteristics I hope to get from PIO and AB resistors. This is not a fidelity project, and it doesn't need to be accurate or good. I can draw an abstract landscape painting when use ink made of amorphous carbon, or I can make it into a resistor to put it down on my audio equipment. They are all the realization of personal abstraction.
If it is obviously not a cost-effective choice for individuals to make industrial-grade resistors, I suggest buying finished products-at least there are enough of these finished products available in China, and the price is not expensive, and the high-resistance resistors range from 40 cents to 10 dollars. Of course, the cheap price is poor performance (for example, high-resistance resistors also have absorption effect, and cheap high-resistance resistors may not use some precious metal oxides, resulting in their large temperature drift). However, compared with those "self-achievement products" of DIY, they are still very acceptable (note that there are many "abstractions" things in the electronic market in China, so don't buy them blindly).
Here are some examples of my tentatives:
The substrate is most often (but not always) PCB material, the resistive material is most often graphite (but not always), and the fillers and binders vary.
There are a few successes, some complete failures and many half-failures
The substrate is most often (but not always) PCB material, the resistive material is most often graphite (but not always), and the fillers and binders vary.
There are a few successes, some complete failures and many half-failures
Continue to record this project.
48 hours and 72 hours after the production, I tested his resistance respectively, and the obvious resistance value decrease which can not be by of multimeter error. I suspect that it is caused by the epoxy resin polymerization shrinkage force pressed for the organic carbon cured product with low strength. After 48 hours, the resistance decreased by 2.14%, and after 24 hours, it decreased by 0.47% on the basis of the above, reaching -2.61%.
I think that the added silica micropowder and shiny mica microplate pearlescent gold powder have played a role in controlling the thermal expansion rate of epoxy resin, and the temperature difference between the two tests is not big (the temperature was not recorded for the first time, and the temperature for the next two times was read by a precision mercury thermometer that can be vaguely read to 0.01 degrees), so it is more likely to come from the release of stress in the later period after shrinkage.
With reference to the standards for resistors such as MIL-STD-202, MIL-PRF-55342, GB/T-5729, JIS-C-5202, it maybe possible to keep this resistor in “cold, normal temperature and hot” cycles for many times, which will make it aging and stable faster. At present, I am doing this project-put it in a dry bottle and put it in the refrigerator for 12 hours (the purpose of putting it in the bottle is to avoid the harm of condensed water later), then take it out and store it at room temperature for 3 hours, then bake it in the oven to 50 degrees, and keep 1h，end for one cycle, and repeat it for 5 cycles or more, hoping that it can age quickly-the aged resistance will be relatively more stable than it is now, so it may have real practical significance to marked for it in that time.
48 hours and 72 hours after the production, I tested his resistance respectively, and the obvious resistance value decrease which can not be by of multimeter error. I suspect that it is caused by the epoxy resin polymerization shrinkage force pressed for the organic carbon cured product with low strength. After 48 hours, the resistance decreased by 2.14%, and after 24 hours, it decreased by 0.47% on the basis of the above, reaching -2.61%.
I think that the added silica micropowder and shiny mica microplate pearlescent gold powder have played a role in controlling the thermal expansion rate of epoxy resin, and the temperature difference between the two tests is not big (the temperature was not recorded for the first time, and the temperature for the next two times was read by a precision mercury thermometer that can be vaguely read to 0.01 degrees), so it is more likely to come from the release of stress in the later period after shrinkage.
With reference to the standards for resistors such as MIL-STD-202, MIL-PRF-55342, GB/T-5729, JIS-C-5202, it maybe possible to keep this resistor in “cold, normal temperature and hot” cycles for many times, which will make it aging and stable faster. At present, I am doing this project-put it in a dry bottle and put it in the refrigerator for 12 hours (the purpose of putting it in the bottle is to avoid the harm of condensed water later), then take it out and store it at room temperature for 3 hours, then bake it in the oven to 50 degrees, and keep 1h，end for one cycle, and repeat it for 5 cycles or more, hoping that it can age quickly-the aged resistance will be relatively more stable than it is now, so it may have real practical significance to marked for it in that time.
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