USB-C port works fine after soldering but becomes unreliable the next day? - Page 1
Forum section: electronics / beginners

author: goof
author_rank: Newbie
timestamp: January 06, 2022, 04:06:26 pm
content: Hi! I just designed my first PCBs for a split keyboard. I don't have much experience with soldering so I hesitated to add Type C USB (2.0) ports but after watching a couple videos on YT where people solder these ports with basic equipment, I figured it can't be that hard.And it didn't feel that bad. A bit tricky at first, but in the end, it seemed like all I need to do is add some flux, bit of solder on the tip, and just get it in there. It'll flow to the right places. Check for bridges with a loupe, add more flux and drag away with clean tip to remove bridges. Then spray some IPA and clean the area with a cotton swab, wait a few minutes, plug it in. No problem, right?Both ports on both halves of my keyboard worked perfectly after soldering. However, the next day, both had became unreliable: wiggle the cable up and down just a little and you'll see a USB disconnect in dmesg. It was so sensitive that simply picking up the PCB and letting the weight of the cable tug it a little could cause a disconnect. Sometimes you'd have to plug the cable in more than once to make a connection.Okay, maybe a cold joint? So I decided to reflow the joints with flux and a little bit of fresh solder, clean bridges again and so on. Same thing, works perfectly after the operation. A day later, and it's cutting out again. Both ports.I repeated the same ritual a couple times, trying to use more flux / different kind of flux / higher tip temperature / bigger tip, but every time the result was the same: works great and then doesn't. I used hot air to remove one port and replaced it with a new one. There were no broken pads or other funky stuff. Again worked it perfectly after soldering, and then the next day it's cutting out. I tried to reflow the solder this time with flux and hot air, again it worked perfectly after the operation and then some time later it's as broken as before?I gotta admit I'm quite frustrated at this point, because I have no idea what I'm doing wrong. Am I actually making bad joints every single time?! Or is there something else going on? Why does it work fine initially but then starts failing some hours later?Molex 217179-0001 is the connector I have. I'm soldering with a pinecil, using the default tip as well as TS-BC2 (bevel, ~2mm diameter). Both tips seem to conduct heat very well and I haven't had issues with any other component in my project. Temp range 300-350 degC (as per the display on Pinecil; not calibrated or measured). Stannol Kristall 400 for solder. The flux I started with was Stannol 500-6B (pen, flows like water), and for the last few rounds I've used a jar of tacky Chipquik SMD29175G.

author: jmelson
author_rank: Super Contributor
timestamp: January 06, 2022, 04:10:17 pm
content: Clean the inside (connector contact area) of the connector with an alcohol-soaked Q-tip or whatever you have available. The heat from soldering may dry out whatever is in there, but then it absorbs moisture and causes issues. Also, clean all flux off the solder pins/pads, same issue as above.Jon

author: tooki
author_rank: Super Contributor
timestamp: January 07, 2022, 05:28:13 pm
content: I would strongly recommend using commercial flux cleaner, not IPA, because many fluxes contain activators (or the “wastes” of spent activator) that are not alcohol soluble, producing residue that can be conductive. These often appear as chalky white residue. Commercial flux cleaners are much better in this regard.Note that this also applies to no-clean fluxes (in fact, even more so!) and that no-clean fluxes are only no-clean after being FULLY heated, which is in no way guaranteed to happen in hand soldering. So if you hand solder and add any flux beyond the flux core of the solder wire, thorough cleaning is important.