Very soft solder on PCB

[BurningTantalum]

I have a low profile PC that I wanted to fire up but it only has a DisplayPort output socket. I ordered a DP to HDMI adapter from China which worked fine when plugged in. However after an hour's use it died so I opened up the case on the HDMI socket end. Inside was an 8 pin unmarked chip (microcontroller) and a few other peripherals. The soldering on the terminations of the short lead from the DP plug looked dodgy so I had a look under a microscope and the solid core wires (14 of) looked as if the solder had not wicked as if they were varnished and not cleaned off prior to soldering. I had a gentle scrape with a scalpel and to my surprise the copper seemed to disappear and the inside was extremely soft and very shiny. Then I realised that the solder on the pads was also very soft and could be pushed around with the knife. It has the consistency of something like room-temp milk chocolate. I scrubbed at it with a stiff toothbrush and IPA and it just smudged off the pads and ended up everywhere. I had intended to flow more 60/40 on the pads and then suck it off and repeat but I'm wondering what the 'solder' actually is, and if the wires are really aluminium. The solder on the rest of the PCB seems to be the same. I opened up the small case on the other end of the cable (DP plug end) and the soldering is the same if not worse. The copper-coloured wires just sit in a meniscus of 'solder'. Any ideas as to what I have found?
BT

[amyk]

Pictures please... but I suspect what you have is hardened solder paste (flux with microscopic balls of solder) that for some reason hadn't gone through the reflow oven.

[Psi]

I suspect what you have is hardened solder paste (flux with microscopic balls of solder) that for some reason hadn't gone through the reflow oven.

It probably has, just not for long enough, or the oven had a cold-spot.

It could be that ultra low temp solder got used accidently, or that someone reworked it and mixed leaded and lead-free together to make low melting point solder.
But a failed reflow process that wasn't long enough or hot enough is much more likely

[BurningTantalum]

Thanks, that would explain the slightly granular looking soft solder. I didn't think of the possibility it could be 'uncooked paste'. The 'copper' wire is definitely odd in that I scraped it very gently with a scalpel and it was also so soft that I must have removed about 1/4 of its diameter which was very shiny and silver. I will experiment with resoldering the connections tomorrow. I don't know if this was the cause of the failure, so before I do any more I will check the lead through for continuity on all pins. If the cores are copper-plated aluminium and the cause of the fault I will replace the whole short lead with a section of real copper lead from an HDMI cable.
Thanks for the info. BT

[tooki]

Why not just use a DP-to-HDMI cable?

[BurningTantalum]

As far as I know the two protocols are completely different, hence the electronics in the small case on one end.
After further examination and poking the solid single core conductors are indeed aluminium coated with copper. The solder fooled me initially as it looked like lead-free but was probably partly heated paste, and also seemed to have not been fluxed so had not tried to wick onto the copper plating. I didn't think it worth replacing the 100mm length of cable so reflowed the terminations and the pads on the PCB components with a bit of 60/40 and tried it - The unit sprang back to life. Another example of shoddy Chinese quality control, or simply someone scavenging the reject bin and selling the contents, but at least I learned something from it - $4 well spent !
BT

[tooki]

As far as I know the two protocols are completely different, hence the electronics in the small case on one end.

Of course they're completely different. But every graphics card DP output port can change what signals it outputs.

There are two kinds of DP-to-HDMI adapters/cables: active and passive.

Active converters use an actual chip to read in the DP signal, convert it, and retransmit as HDMI. For a while, this was the only way to get 4K/60Hz HDMI output from DP, though newer cards with newer HDMI versions can do it with a passive adapter.

A passive adapter contains no electronics. It shorts some ID pins to tell the graphics card "hey, I'm a passive HDMI adapter" or "I'm a passive VGA adapter", which the graphics card reacts to by outputting HDMI or VGA signals on the DP port. (These "alternate modes" were designed into DisplayPort from the start, so the ID pins and the pinouts of the adapters are standardized.)

DisplayPort's ability to switch modes is also how Thunderbolt works: it uses an alternate mode to essentially send PCIe packets over DisplayPort.

(Disclaimer: I'm not 100% certain on the official terminology and haven't looked it up.)

[SiliconWizard]

It sounds like SnBi solder, which can be handy for hand-prototyping or if dealing with specific parts that can't be reflowed at high temperatures (which is now rare), but is complete crap otherwise.