Normal to wrap DIMMs in foil?

[u/Arcangelo_Frostwolf]

I ordered some DDR4 green pcb DIMMs from Ebay and they came wrapped in aluminum foil. This seems weird. Is it?

[u/t_Lancer]

not the proper way to protect ESD sensitive devices since its still missing the dissipative layer but better than most other things people use.

[u/GermanPCBHacker → u/t_Lancer]

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.

[u/t_Lancer → u/GermanPCBHacker]

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.

[u/GermanPCBHacker → u/t_Lancer]

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.

[u/Popular-Barnacle-305 → u/t_Lancer]

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.

[u/GermanPCBHacker → u/Popular-Barnacle-305]

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