NASA's Through-Hole Workmanship Req (2002)
workmanship.nasa.gov
workmanship.nasa.gov
1) On page three, that exposed end of the lead is a defect if you're NOT going to conformally coat the board. If you don't know what a conformal coating is, it's a defect.
2) On page eleven, flux residue. Sure, for NASA's applications. For most commercial applications, the IPC rule is "excessive flux residue". For prototypes, one-offs, and hobby projects, my rule of thumb is, if you can't measure the difference removing flux makes, leave it there. Incompletely cleaned flux can be more corrosive than undisturbed flux. Also, no-clean flux should be called "never clean" flux. Never clean it with ordinary methods because you will never get it clean.
Beginners should not ever clean flux. Most hobbyists should never need to clean flux. Professionals should have data driving any decision to clean flux.
I never considered flux compatibility between my solder rosin core and the flux paste and never considered measuring salt residues on the board.
I almost exclusively use the same Kester sn64pb37 rosin core solder and MG Chemicals #8342 RA rosin flux paste. Both must be cleaned promptly. Now, I don't bother cleaning if I don't intend to use the board after I test it (like when I do prototyping) but anything else gets a thorough wash. I use various PCB cleaners, typically ethanol (not IPA!) based and then rinse boards in electronic water. I never saw any oxidation on any of the traces unless there was some external contamination.
https://nepp.nasa.gov/whisker/
I thought they were just one of those low probability items until a Sunday morning when I was running live audio for a church service. Singer was mid verse and BOOOOM! Huge booming sound over speakers startling everyone into nervous laughter. I opened the cable up afterwards and sure enough found these alien crystalline structures growing between the conductors. It had shorted and even the little bit of current in the microphone vaporized about a mm of material.
Really really weird and I'm certain kept some folks up at night over the years.
Why would an engine require leaded gas, you ask? Because it helps keep the valve seats from degrading. We have other anti-knock additives, but nobody has figured out a replacement for the other properties that lead has.
And since aircraft are usually extremely long-lived, we'll be stuck with this problem until a substitute is found. Merely certifying new engines that don't require lead won't solve the problem because of the remainder of the fleet that does require leaded gas.
Essentially, we still don't have a viable replacement. The FAA was tasked with coming up with one by the end of 2018, but has been extended to 2021.
Did you read their specs?
There's a small part about whiskers that already convey enough meaning:
> UNACCEPTABLE WHISKER
> A whisker is a slender needle-shaped metallic growth between a conductor and a land. Typically the result of mechanical stresses in high tin compounds, it is a reliability concern."
'Please don't comment on whether someone read an article. "Did you even read the article? It mentions that" can be shortened to "The article mentions that."'
It doesn't add anything to the discussion. And in this case it was very clear that the OP read the article and just missed that part.
Your comment would have been just as informative and less snarky if it was simply:
There's a small part about whiskers that already convey enough meaning:
> UNACCEPTABLE WHISKER
> A whisker is a slender needle-shaped metallic growth between a conductor and a land. Typically the result of mechanical stresses in high tin compounds, it is a reliability concern."
> 'Please don't comment on whether someone read an article. "Did you even read the article? It mentions that" can be shortened to "The article mentions that."'
Not an article, but specs. You read specs carefully, you don't skim, especially to write long paragraphs about your personal experience
> And in this case it was very clear that the OP read the article
I disagree. Not read, skimmed at best.
> and just missed that part.
I agree: the most important part was indeed skipped.
You're factually wrong here. So the question would be where did this go off the rails?
The issue with whiskers is that they grow over time (which is why I mentioned 'point in time'). I didn't see anything in there about solder alloy selection or any other mitigation.
Sorry for the misunderstanding then.
Conformal coat really is the saving grace for tin whiskers. It's not perfect, a whisker can push through sometimes but then the whisker has to push back through the conformal coat again which is much harder.
About leaded solder and the environment: "Current alternatives are worse for the environment",page16 https://nepp.nasa.gov/whisker./reference/tech_papers/2011-ko...
I need to take a course.
Unless you're sending your stuff to space, I suspect you can cut yourself a bit of slack here. :)
No harm, no foul is what I mean to say, haha.
I used to work with a developer whose second job was with HP back in the 70s. He was hired as a technician building lab equipment and had to be prequalified from an educational and trades/skill perspective to be hired.
Then they taught him to solder again. Their standards were apparently incredibly high.
But I flick the little switch and the little fan comes on and I am happy.
But I should do a course. Or at least google some more. I don't even know many of the terms people are using here...
I want to share some of my thought on soldering: The best way to understand soldering is to think primarily in terms of surface tension or capillary action and intermetallic compounds. You set it up correctly and apply heat so that fluid dynamics can finish the job. The atoms get to where they are supposed to be. There is no technique or dexterity required with the soldering iron itself. I would also recommend that you think of solder wire as a 2in1. The flux core in the solder wire is helpful, but not the endgame. Use extra flux from a flux pen or flux bottle that is compatible with the flux core in the solder wire. For example: You can put a glob of solder on the tip of your soldering iron and just bring it in to the surface or joint. If you have pre-applied flux on a clean surface or joint, the liquid solder will wick off the soldering iron and onto the surface by itself. Perfect every time. (Surface tension, capillary action.)
For manual hand soldering, the flux management is the only complicated part. What flux to use? Do you have to clean it? How to clean it? Saponifiers, or IPA good enough? Compatible with the flux in the solder wire? You must be sure to reach the activation temperature of all the flux on the board or it can corrode metals over time. "No Clean" fluxes are really hard to clean without special saponifiers, I would avoid these fluxes. Is the flux residue on the board still inert after it gets wet by accident or at high humidity? There are also problems with high frequency circuits and No Cleans. Water soluble fluxes require excellent process control. Even tiny defects in the PCB can cause failures if you use water soluble flux. Read the datasheets and recommendations from the flux manufacturer.
Some fluxes are more easy going: For you Americans I would recommend Kester 186 Flux-Pen and Kester 285 Sn63Pb37 RMA Flux-Cored Wire. Do not use more flux than necessary, do not make a mess. Use eye protection for this flux from Kester!
Soldering gets even more interesting with gold embrittlement (gold plating thickness and migration to the center of the IMC), tin whiskers, silver whiskers, etc. There is much more to all of this if you want really high reliability. I went deep down this rabbit hole once. Not a professional soldering guy. Just obsessive compulsive about high reliability design. This is enough text for a post on HN :)
Don't have a source unfortunately other than personal experience working as an engineer.
That and, people who hand solder stuff all day are fast.
I’ve see the videos on IG every now and then on their hand soldering skills. So fast!
Really, learning how to braze and weld steel helped me a lot. Heat control is extremely important. Heat flows, and you learn how to position your iron to get the heat where you need it. You can also tell how hot something is by how the puddle looks.
Then practice with PVC insulated wire. The PVC insulation shrinks if it gets hot so this is good practice at speeding up.
I looked through the NASA document and most of it is not advance technique.
EDIT: people are saying "good tools" and I wanted to say a bit more about that. You can buy an iron for a few dollars from ebay. Don't use those. But almost any iron above that is going to be fine. I'd prefer to always be using Weller or Hako, but failing that any of the chinese no-name irons with temperature control are going to be good enough for most hobbyist projects. I love my Lindstrom and Bahco snips, but you can get good-enough cutters much cheaper. If this is something you're going to be doing all day every day you'll want to invest in the tools.
If you're looking for a practical way to do this, consider hand-wiring your own keyboard. I did this a couple years back, with 75 keys or so. With the diodes on each key, it was about 225 solder joints plus whatever extra to land the matrix leads on the microcontroller.
Good variety, too. Some were wire-to-wire joints, others were wire wrapped around post, and a few where through-hole joints.
If I look at the underside of that keyboard, I can tell where I started and where I finished by how clean the solder joints look :)