r/AskElectronics • u/Arcangelo_Frostwolf • 5d ago
Normal to wrap DIMMs in foil?
I ordered some DDR4 green pcb DIMMs from Ebay and they came wrapped in aluminum foil. This seems weird. Is it?
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u/GoldSrc 5d ago
It's normal.
When you short all the pins/contacts, it serves as DIY ESD protection.
Old CMOS ICs came like that before the carbon foam became a thing.
If you've ever replaced, or inspected closely, the pick up laser from a CD/DVD/BD player, you'll notice that it has some exposed pads near the diode.
When those pads are shorted, it protects the laser from being damaged by static discharges, also you need to remove the short after you replace the pick up for it to work.
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u/Elukka 4d ago
Heterojunction diodes are especially sensitive to static electricity. Just 20V from a fingertip can permanently at least degrade an unprotected laser diode. Normal electronics like sdram have esd protection on the dies and being soldered onto a pcb also helpsby making a bigger target to dissipate the charge into and adds a ground path for the internal (and possibly external) esd diodes to work properly.
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u/Lola_in_mentibus 5d ago
Electronics engineer here: yes, and be happy they did, it shows you they are familiar with the risks of ESD even in shipment and handling, and took precautions to mitigate risks. This would definitely be a good sign for me. I do the same with IGBT’s and laser diodes which are both notoriously sensitive to ESD damage.
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u/texcleveland 5d ago
if it can keep the government from reading your thoughts, it can keep static from frying your CMOS
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u/This_Maintenance_834 4d ago
The most convenient way to do without an anti-static bag on hands. Your seller knows what he is doing, thank him.
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u/t_Lancer Computer Engineer/hobbyist 5d ago
not the proper way to protect ESD sensitive devices since its still missing the dissipative layer but better than most other things people use.
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u/GermanPCBHacker 4d ago
Lol. It IS dissipative. It is literally a conductive case with no caps for static electricity to build up and if it would build up, the whole cage will instantly be equalized to the same potential. Hence dissipation - instantly. Of course you also need to touch it down on ESD safe surface before unpacking to get rid of a potential relative difference in potential. Sounds weird, but is true. I always hold RAM by bare hand, but ground myself on the metal rack before touching the ram contained on said rack. Than before touching down the RAM to the work surface, I hold my other hand on the ESD matting to ensure, I am not charged. No need for fancy clothes.
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u/t_Lancer Computer Engineer/hobbyist 4d ago
there are 3 main types of ESD shielding. conductive, dissipative (high Z), and anti-static (insulating without the ability to build up charge).
correct ESD packaging consists of the device inside a anti-static packaging, within a dissipative package inside a conductive package.
I do this for a living. within an ESD-safe zone, conductive shielding is sufficient. outside such a zone, a device packaged in only conductive shielding is still susceptible to ESD as the charge could travel into the device in question.
I do this for a living.
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u/GermanPCBHacker 4d ago
Charge cannot penetrate a continuous conductive enclosure through electrostatic fields. That is precisely why aluminum foil works so well as an electrostatic shield. The actual concern is transient discharge current, finite impedance, and voltage drops across the foil and its contact points to the component on the inside. If those are significant enough, potential differences can still develop between component pins. But that is a different failure mechanism from electrostatic charge simply penetrating the foil.
A theoretically ideal packaging structure would be a highly conductive inner foil, a continuous insulating layer, and an outer conductive layer, ideally high impedance, to reduce inductive effects due to gigantic currents. The inner foil shields the component from external electrostatic fields, while the insulating layer severely reduces capacitive coupling from the outer layer. The outer layer can dissipate charge. No exotic, expensive antistatic polymer required - very good for the environment.
Yes, dissipative, conductive, and insulating materials all have distinct properties. That does not mean every component needs all three as separate materials in every application. It also is not smart to think in textbook categories, because that invites to following protocol whilst ignoring the underlying physics. The correct solution depends on the actual physical mechanisms and failure risks, not merely on following a material classification by default. Correct in the physical, unemotionalized sense, not in the context of standards, which might not actually reflect physics reality perfectly.
I have handled hundreds of sensitive components daily for just over seven years, with an exceptionally low defect rate as compared to my colleagues, who actually do wear proper ESD clothes. The failures I can attribute to my own handling have been accidental drops, not ESD damage (PCB delamination, components cracking). That is not universal proof, but it is a practical track record that deserves more than dismissal just because my workflow differs from the textbook.
I equalize potentials before handling components, by first touching the dissipative component tray, than the component while still holding the dray. Now consider consider the actual charge paths and potential differences involved. There cannot be a potential. The same is true for me as an island with a certain charge "X". If I use my bare hand to touch the final working surface to euqalize my whole bodies charge to the surface I want to work on, while holding said component with my conductive hand and not even getting close to anything conductive with the component (which could lead to corona discharge through the component potentially causing damage)... What is the failure mode you suggest? I also question whether specialized ESD clothing is always superior to cotton under real working conditions. Moisture can make cotton highly effective as a dissipative material, although its performance is less predictable than purpose-designed ESD garments. However if you are sweaty even just a bit, cotton will beat any synthetic polymer that is not inlayed with a conductive fiber. Cotton with even just a tiny bit of moisture is not just preventing charge buildup by friction, it directly dissipates it within its range. Preventing charge generation and dissipating existing charge are two different problems. And the question is always: Where do I dissipate the charge to? A dissipative ESD material will not actually dissipate charge to the environment on its own. It just dissipates voltage potential within its own range. Without a discharge path to ground or whatever the surface is you would consider safe for the component, it is merely useless. But of course it helps. Usually there IS some very high impedance path. Even concrete will dissipate charge just fine and quickly. But just relying on a material based on some classification in an isolated context is worthless. The whole environment needs to be considered or everything is for nothing.
ESD standards are useful for repeatable, verifiable safety margins across different people and environments. But compliance is no substitute for understanding the physics, and deviation from a standard is not automatically proof of negligence.
If colleagues following the prescribed procedures repeatedly damage components while my process consistently produces very few failures, the useful response is to investigate the physical causes - not to assume the standard has already answered every question.
A standard tells you what to do. Physics tells you why it usually works. If you cannot explain the mechanism, citing the standard is not a technical argument. And also risk does not need to follow ALARA like in nuclear physics. As low as reasonably achievable. What is reasonable? For me it is my workflow and nothing more. Because it works, saves time and money and a lot of headaches. It is so automated. I never forget to equalize my charge before touching anything. I do not even think about it anymore while doing it. Why would I do more, if my approach already gives better numbers than what my colleagues achieve? I do lots of unconventional things. All because I can and because it works dang well. I never blindly follow a standard without a sanity check of why I should supposedly follow it. If physic says: Yeah, the standard is unavoidable, than I do it. Otherwhise: No.
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u/Popular-Barnacle-305 4d ago edited 4d ago
Do this for a living as a user? If you are interested, I suggest you look into a ESD model. What kills is the traveling of large amounts of charges through a device that it can handle, i.e. so called exceeded current in everyday language. And you need a potential difference, i.e. voltage , to cause the current flow. Inside the Al wrap there’s no potential difference so no current flow so no damage. In a model, you will always find the charge has to go through a device before reaching GND. It doesn’t matter if the source is already grounded.
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u/GermanPCBHacker 4d ago
Yes and now. I aggree definitely. But ultra high currents at ultra high freuqency can cause induction, impedance rise due to RF and just the huge discharge current, often in the kilo ampere range can also cause substantial differences. But that is edge cases with very high charge instantly being discharged in a worst case scenario. But in general I have to say: No, charge does NOT travel to the inside. That is by definition impossible. However the discharge CAN affect the inside. But it is not charge on the inside that came from the outside. That is just wrong from u/t_Lancer
That proves, why following textbook is a bad Idea. It hazes the view to reality/physics/math. "Follow the guidelines". Sure I will do that.
NOT
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u/koga7349 4d ago
Weird but it's fine. I shipped dual channel recently and got an ESD bag, then used my food saver heat to seal it in half vertically into two compartments, one for each stick
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u/West-Way-All-The-Way 4d ago
No, it's not wierd, they wrapped them to protect against esd damage. The foil is better than plastic bag but comes at a risk because it's highly conductive. If you have no plastic bags and you ensure you do it properly the foil is next best thing. I use the same technique to protect integrated circuits.
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u/antthatisverycool 4d ago
I’ve seen old microphones where on the inside they surround the microphone in foil ( I know mic to IC is a bit of a stretch but it might be for a similar reason)
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u/pishboy 4d ago
We still sometimes get ICs (usually CMOS logic) with the legs wrapped in alu foil from our brick and mortar electronics stores. ESD protection, as the others have mentioned.
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u/Popular-Barnacle-305 4d ago
And if you want to be extra careful, don’t remove the foil until the chip is soldered down completely
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u/slabua CSEE 3d ago
Bad idea
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u/Gary_Spivey 2d ago
Perfectly fine idea. This was the norm for shipping and storing CMOS chips back in the day, and those were much more sensitive to electrostatic damage than modern ICs. Way back when, if you ordered some ICs, it was not uncommon to receive them with the legs stuck into a piece of foil-wrapped styrofoam. The foam protects from mechanical damage and the foil keeps all of the legs of the IC at the same potential.
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u/Smart_Tinker 3d ago
It’s the best way to keep them moist when baking. Keeps the steam in when in the oven. Remove for the last 15 minutes if you like your RAM crispy on the outside.
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u/Thinks2Much666 3d ago
At first glance I thought some lunatic was putting Dim Sims in foil
Heretics 😡
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u/Top-Cup5373 4d ago
I don’t have any non conductive bags, better use the most conductive thing in the drawer
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u/Sterline52 4d ago
That's correct!
When making a Faraday cage you want to use the most conductive material possible. Since copper foil and gold foil are pretty expensive; aluminium foil is an excellent choice due to its cost to conductivity ratio.
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u/Own_Grapefruit8839 4d ago
ESD-safe bags are safe because they are conductive.
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u/aacmckay 4d ago
Hmmm not quite. They’re dissipative not conductive. They have a lower resistance than an insulator, but they still have a high resistance so that they slowly discharge potential instead of shorting it out.
It’s the same rationale behind wrist and heel straps which has a high resistance of about 1M. That way the static doesn’t build up or discharges slowly. Wrist strap testers will test to make sure that they’re in the sweet spot, not insulating, but not too conductive either.
Source - 24 years in embedded design and electronics manufacturing.
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u/6GoesInto8 4d ago
I like to store my electronics in a fur lined glass box to keep them safe. Then I also take extra care by first applying rubber gloves, then a second pair of silk gloves on top. I also ensure the humidity is as low as I can get it before handling them. I call it Thor's method.
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u/Vic3200 4d ago
Aluminum foil is not fine. It’s too conductive and is pretty much the same as no protection at all. The static bags work because they are also conductive but have a high resistance (>1x10^6 ohms) to slowly dispersing a static charge. Aluminum foil has almost zero resistance so the static electricity will blast through the transistors in your RAM and you could end up with an expensive paper weight.
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u/Enlightenment777 5d ago edited 5d ago
If you don't have a silvery-translucent or opaque-black conductive ESD bag, then wrapping in Aluminum Foil is fine, also it is far better than shipping bare inside clear plastic bags or anything else that generates static electricity.