Soldering thread

[paul1598419]

Back in the early 1970s I was a shop Tech for a large retailer of televisions while going to school. I carried a magnet around in my pocket protector and none of the leads to caps were magnetic back then. In fact the leads to all components were nonmagnetic back then. Everyone had these telescoping magnets as screws would find their ways into places where it would be difficult to retrieve them. No components back the would stick to them.

 

[Benm]

I just noticed by chance - i was working on a project and had a small Nd magnet laying around on the desk, and noticed resistors stuck to them by the leads. These were fairly recently bought (as in the last 5 years or so) and stuck. I tried with some older ones i had in store and those are not ferromagnetic at all.

As far as I can retrace is the magnetic ones came in an order from Futurlec, but it may be a common thing nowadays.

I've tried with some more components, and found roughly this:

- resistors: very variable, some strongly magnetic others not at all
- electrolytic caps: all i could find attracted
- ceramic caps: some magnetic some not
- transistors, mosfets (both small signal and power): none were magnetic
- diodes: 1n418 magnetic, 1n4007s and similar cased schottkey diodes: none magnetic
- ic's (opamps, current regs, microprocessors, logic chips): none were magnetic.

This is just a small sample of components i had close to hand, but it seems that ferromagnetic leads are common in some components. I have not any difficulty soldering these components, but it seems like they have tin plated steel wires instead of good old copper.

Makes you wonder about durability in wet environments though, i'm quite sure tin plated iron does corrode fairly easily and crumbles. Copper corrodes as well but doesn't break down as the oxide layer prevents corrosion beyond the surface.

I think this is a fairly realistic problem as i've seen older electronics where for example a switch just had its connections rusted through to the point where it didn't conduct any longer while the rest of the circuit was intact. This was not the result of the product actually getting submerged or anything like that, just a few decades of normal use.

 

[paul1598419]

I guess it is another example of planned obsolescence. I sure hate to hear these axial resistors are now made out of iron.

 

[Benm]

I have my doubt that's the reason behind it - i think it's just cutting costs wherever possible. These things literally cost 1 cent each even in small volumes (like 100 pieces for $0.99), probably a lot less in bulk - i've seen listings of 1000 pieces for ~$3 on ebay.

Using rusting wires for obsolescence isn't the best idea either i guess, as they are very visible and then easy to repair.

Somehow i think the amount of copper required is just too expensive to compete on the market and they resort to cheaper materials to cope.

Interestingly this seems limited to through hole resistors for now, i've never had a surface mount one that was noticeably ferromagnetic. I guess components in MELF packages could be susceptible as well, but i never use those.

 

[paul1598419]

The planned obsolescence was a joke. Of course copper is much more expensive than iron. In the end, I might pay more for one with copper leads as long as the price wasn't drastically increased for them. I have thousands of resistors in my stock and if the unit price were 2 cents for iron and a dollar for copper, that would be ridiculous.

 

[Benm]

I don't the difference in price is that dramatic really, at least not for the hobby user. Perhaps the copper leaded ones were $2 per 100 and the ferrous ones are $1 per 100. That's obviously double the price, but considering the cost for just the resistors in any project the total difference would be negligible.

What surprised me is what components they do these ferromagnetic leads on, and what ones they do not: They seem pretty common on resistors and capacitors, but i've never seen them on transistors.

Those transistors also are really cheap, i get the small signal ones like bc 337's in bags of a 100 pieces costing about 3 cents each at that quantity, but they never have ferromagnetic leads on them.

With components this cheap i usually just buy them in bulk - even if i only need 2 transistors right now i'll just the the bag of 100 since they are only a few bucks and always come in handy at some point.

So it doesn't seem that all -cheap- components now come with ferromagnetic leads, just mostly passives, but also small signal diodes so i doubt it's not used because it is somehow incompatible with semiconductors.

 

[paul1598419]

My point exactly, if you didn't get that from my posts. I often buy in bulk too and don't mind paying double what I would for these components. In the end, they will likely last longer, especially if they are exposed to moisture somehow.

 

[djQUAN]

It is mostly about the price. Copper prices have increased dramatically. If you are a manufacturer, saving $0.001 per part is a lot if you plan to make hundreds of thousands to millions of products, multiply that by the number of parts inside each product.

For electrolytics, I think it would be partly because of strength. These are heavy parts mounted on 2 leads. Bigger caps have stamped pins riveted to the base.

Transistors usually use copper wireframes because of the stamping process and heatsinking of the die (same with ICs). Even low power transistors dissipate some heat.

 

[Benm]

I'm fairly sure with the resistors it is a cost cutting measure, i've also noticed that the leads have become a lot thinner over the years, sometimes so thin they are hard to use on those solderless prototyping boards due to low contact pressure.

And yeah, shaving off part of a cent of component cost does make sense when you produce things by the millions. The downsize of it's now fairly hard to find resistors with properly thick, copper leads at all - even if you are willing to pay double or triple. It's rarely even specified in listings.

For soldering this als does have consequences: Copper actually dissolves to a small degree in tin/lead solder and makes mechanically very strong bonds - the entire joint is essentially an alloy with a gradient between pure copper and tin/lead (near) eutectic mix .

If you try to yank a 80/90s era resistor from a circuit board by brute force (wedging a screwdriver under it and pushing down etc), you'll break the resistor in half. With the components nowadays you'll most likely break one of the leads, or the solder joint and just rip the lead straight out of the board.

Usually this is not a big deal, but it's something to consider when you design a product where a solder joint takes a mechanical load beyond the weight of the component itself.

 

[Seoul_lasers]

This coming school year I get to be the head of MYP design at a new international school in town, manage a makerspace and teach soldering skills! I will be showcasing some projects my students build.

I am looking forward to posting more content. We are also going to build some lasers! That I promise.

 

[paul1598419]

Nice to see you posting again, Seoul_lasers. Looking forward to your laser building. + Rep.

 

[Sterling532]

I have some left over Indalloy soLder rosin flux #5RMA made by Indium Corporation of America. Originally bought to help out folks making DPSS on Sam's Laser FAQ but I still have some sitting around. You are welcome to a 30 ml re-fill sample if you can use this for a project. Special deal for anyone reading this post... one dime for 30 ml and I can ship it at cost.
https://sro-optics.com/shop?olsPage=t%2Fmisc

 

[paul1598419]

This is just flux, right? I mean it was meant to be used with indium solder, but it is rosin flux, isn't it? I would be interested in an ounce of it if that's the case.

 

[Sterling532]

Yes, just the rosin flux designed for low temp soLder work like indium. The indium and soLder are long gone. Sorry for describing awkwardly. The above link will get you to this special deal. Sharing what project you are using it for is a bonus for me.

-sterling532

 

[paul1598419]

Thanks. I placed an order for it just now. I look forward to receiving this liquid flux. 30ml is a full fluid ounce, so that is a pretty large amount of flux. I plan on testing it to see if it will work with some of my laser projects I have coming up soon for other member here.