Anticept Posted June 21 Report Share Posted June 21 Remove the old solder because it will be contaminated. Rosin core solder at minimum but I recommend potted flux. More flux when soldering is better, just don't breathe it. It helps you control temp easier and finish the joint. If you burn off the flux during soldering, the joint is compromised. Dab some on the spot to be soldered and dip the wire for a thin coating. CLEAN IT THOROUGHLY AFTER as flux is corrosive. That "no clean" stuff should still be cleaned. If you dont mind lead, sn63pb37 is the best solder alloy for the application. It is eutectic (melting point is lower than the individual elements) which means it will form an extremely strong bond. Otherwise, K100LD is a decent bet. Quote Link to comment Share on other sites More sharing options...
Madhatter Posted June 21 Report Share Posted June 21 Electronics solder flux is not corrosive. You are not soldering water pipes with acid flux. Rosen core solder is used in all electronics, never acid flux. Quote Link to comment Share on other sites More sharing options...
Anticept Posted June 22 Report Share Posted June 22 https://app.aws.org/wj/supplement/WJ_1980_10_s289.pdf It's older material, but makes the point: supposedly non corrosive electronic rosin flux is indeed corrosive in different conditions due to additives. There are fluxes that exist that don't corrode in my experience, but plenty that do. Redid two solder "clean free" jobs years apart. https://ieeexplore.ieee.org/abstract/document/4914727 Many no-clean fluxes for electronics do contain acids and needs to be thoroughly heated to boil off the acid and if not done, it will remain corrosive. https://www.edn.com/flux-residues-can-cause-corrosion-on-pcb-assemblies/ Has some other info about how fluxes work and real world challenges. Now I just clean with HIGH PURITY IPA and toothbrush because I don't have the patience to do research on the all the flux compounds out there and all their silly nuances. Quote Link to comment Share on other sites More sharing options...
Madhatter Posted June 22 Report Share Posted June 22 I've been soldering electronics since 16 and owned an avionics repair station. It's not rocket science, there are standard practices to be adhered to. Quote Link to comment Share on other sites More sharing options...
Anticept Posted June 22 Report Share Posted June 22 22 hours ago, Madhatter said: I've been soldering electronics since 16 and owned an avionics repair station. It's not rocket science, there are standard practices to be adhered to. Just gonna... emphasize that. Nice and big. We should be giving advice based on people's probable skill level, not our own. That means telling them to clean it, they will know otherwise. Quote Link to comment Share on other sites More sharing options...
Madhatter Posted June 23 Report Share Posted June 23 My point to this forum is to provide correct information for those who may have the skills to do the repair. If they don't and do it anyway at least they have some guidance to go by. I don't know what others have as experience and it really doesn't matter in this case. Re-soldering printed circuit boards is not like putting two wires together, it takes a little skill not to damage other components with heat as lead wires are extremely short. It's best to have someone do it who knows how, I don't know how else to convey this message. I think this subject is pretty much played out, at least for me because I have to go out and pick up horse poop. Now that's something I'm really good at Quote Link to comment Share on other sites More sharing options...
FlyingMonkey Posted June 24 Author Report Share Posted June 24 I flew a few short hops over the weekend with zero issues, but then again this morning on my pre-taxi the flaps failed to cycle with the same symptoms. I pulled the relay board (PITA!) and there's some pictures below. The first two are just overview of the front & back of the board, and the rest are some areas where I noted the red sealant is cracked around solder points or worn through revealing bare metal. Is it possible some of the raised areas rubbed clean and shorted/grounded against the carbon fiber firewall? CF is mildly conductive IIRC. There are plastic standoffs for the board but maybe a hair too short? From here, am I correct that I'll have to remove all of the red sealant with acetone and then carefully inspect everything underneath? Or maybe just around the solder points? The sealant looks pretty thick and tough, should it come right off or need some work? Thanks! Quote Link to comment Share on other sites More sharing options...
Madhatter Posted June 24 Report Share Posted June 24 Sure looks like a failed solder joint, seems to have pulled away from the board. I suppose you could carefully clean the coating off. Be very careful on how much heat you apply with the soldering iron. You need something like this. Quote Link to comment Share on other sites More sharing options...
FredG Posted June 24 Report Share Posted June 24 Looks exactly like the one that failed on my relay board. Same location, I think. As you have already read, a soldering tool (iron) with adjustable temperature and a fine tip are needed for this. Madhatter has emphasized, too much head and you can damage components. Too little and you get a cold joint. Also, that red laquer is removable with acetone on a q-tip. Quote Link to comment Share on other sites More sharing options...
Towner Posted June 24 Report Share Posted June 24 Looks just like the previous pics of bad solder joints. That’s why I wouldn’t have had a clue without the previous pics posted on the forum. If I’m understanding your question correctly, Just clean around the joint and not the entire board. I believe it was Corey who remounted the board to the firewall using something to dampen vibration. Probably a good idea too. Quote Link to comment Share on other sites More sharing options...
FlyingMonkey Posted June 24 Author Report Share Posted June 24 Thanks guys. Is there a temp recommendation for the soldering iron to get a good joint without harming anything? I’ve got at least two joints with cracked sealant like that, so I might have to inspect a few different areas. Quote Link to comment Share on other sites More sharing options...
FlyingMonkey Posted June 24 Author Report Share Posted June 24 Upon cleaning, I found four cracked joints. Most are very minor but will get fixed, this is the worst. Quote Link to comment Share on other sites More sharing options...
Madhatter Posted June 24 Report Share Posted June 24 Some solders have different melting temperatures. Best to stay away from box stores and hardware stores, get it from electronics supply stores. They will have small diameter rosen core solder. Small diameter solder will melt quickly due to less mass. You don't need to pile on solder, just enough to coat the connection so you don't overheat it. Do it quickly and don't let it spread out and short adjacent conductors Quote Link to comment Share on other sites More sharing options...
FlyingMonkey Posted June 24 Author Report Share Posted June 24 15 minutes ago, Madhatter said: Some solders have different melting temperatures. Best to stay away from box stores and hardware stores, get it from electronics supply stores. They will have small diameter rosen core solder. Small diameter solder will melt quickly due to less mass. You don't need to pile on solder, just enough to coat the connection so you don't overheat it. Do it quickly and don't let it spread out and short adjacent conductors Sounds good. I think FredG said when he did it he didn't even add solder, just got the existing solder to re-flow. Is that a good strategy or does that mean leaving heat on the board too long? Quote Link to comment Share on other sites More sharing options...
FredG Posted June 25 Report Share Posted June 25 I would want input from others with printed circuit expertise, but I would say 700 F is a reasonable temperature. You do want solder to flow and close the fracture. You do not want it bridge to the foil on the PC board right next to that failed connection, however (you knew that...). I use 60-40 (lead-tin) rosin core electronics solder. Very thin diameter, as Madhatter said. If you don't have soldering experience, make sure the tip is clean and has a small amount of solder on it (i.e., "tinned"). It will transfer heat better. Quote Link to comment Share on other sites More sharing options...
FlyingMonkey Posted June 25 Author Report Share Posted June 25 30 minutes ago, FredG said: I would want input from others with printed circuit expertise, but I would say 700 F is a reasonable temperature. You do want solder to flow and close the fracture. You do not want it bridge to the foil on the PC board right next to that failed connection, however (you knew that...). I use 60-40 (lead-tin) rosin core electronics solder. Very thin diameter, as Madhatter said. If you don't have soldering experience, make sure the tip is clean and has a small amount of solder on it (i.e., "tinned"). It will transfer heat better. I’ve done soldering but I’m no expert, I’ll take all the tips! Should I start colder and creep up the temp until the solder flows, or go right to 700? Quote Link to comment Share on other sites More sharing options...
Anticept Posted June 25 Report Share Posted June 25 Creeping temp is the worst thing, it causes the heat to go into the parts. It should take no more than a few seconds to solder a joint. If you can't finish by that time, stop, let it cool down, throw a thin coating of flux on, heat again. You do need a good tool to remove the old stuff, solder wick is okay, desoldering pumps are better, POWERED desoldering pumps are the bee's knees. 600-650F if you are using leaded solder. 650-700F is best for the lead free stuff. If you have a GOOD iron it should be able to hold temp pretty well. Quote Link to comment Share on other sites More sharing options...
FlyingMonkey Posted June 25 Author Report Share Posted June 25 Thanks Corey. Quote Link to comment Share on other sites More sharing options...
Madhatter Posted June 25 Report Share Posted June 25 700 is way too hot. Around 375F to 400F for electronics. Again don't buy solder from hardware stores. Quote Link to comment Share on other sites More sharing options...
FlyingMonkey Posted June 25 Author Report Share Posted June 25 The solder I have is 0.6mm 60/40 rosin core, the melting temp is listed as 375F. Quote Link to comment Share on other sites More sharing options...
Madhatter Posted June 25 Report Share Posted June 25 Quote Link to comment Share on other sites More sharing options...
Towner Posted June 25 Report Share Posted June 25 Corey, you mentioned previously that when you remounted the relay board to the firewall, you did something to reduce the vibration to the board. What did you do? It’s probably a great idea and I may do it on mine. Quote Link to comment Share on other sites More sharing options...
FlyingMonkey Posted June 25 Author Report Share Posted June 25 1 hour ago, Towner said: Corey, you mentioned previously that when you remounted the relay board to the firewall, you did something to reduce the vibration to the board. What did you do? It’s probably a great idea and I may do it on mine. I'm guessing replacing the hard plastic spacers between the board and firewall with rubber donuts would help. Quote Link to comment Share on other sites More sharing options...
Anticept Posted June 26 Report Share Posted June 26 I've done rubber mounts, it doesn't stop it from happening. I don't even know if its vibrational in nature or if its heat cycling. One of the ugly thing about those relays is they are mounted flush to the board at least on mine, which means NO thermal expansion and contraction. I have to do this repair every few years and not just on mine. Quote Link to comment Share on other sites More sharing options...
FlyingMonkey Posted June 26 Author Report Share Posted June 26 15 hours ago, Anticept said: I've done rubber mounts, it doesn't stop it from happening. I don't even know if its vibrational in nature or if its heat cycling. One of the ugly thing about those relays is they are mounted flush to the board at least on mine, which means NO thermal expansion and contraction. I have to do this repair every few years and not just on mine. Ugh, that's disheartening. Maybe a heat shield between the firewall and the board, with a non-conductive backing closest to the board? Unless it's heat generated purely within the board itself, in which case not much to be done except add a heatsink(s) I guess. I guess I got off pretty easy since mine lasted about 16 years before failing. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.