LGA 3647 discoloration

Discussion in 'Processors and Motherboards' started by Jon, Feb 14, 2020.

  1. Jon

    Jon Member

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    Anyone have experience with discoloration of pads on LGA 3647?

    But only looking at a angle
     

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  2. metacollin

    metacollin New Member

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    Most CPUs of any LGA style package have subtle imperfections like that if you look hard enough.

    It's nothing to worry about. The pads aren't discolored, and in fact the pads aren't really even to blame. The bottom of the interposer (where the LGA pads are) is covered with solder mask. The bottom of the CPU is only green because it is covered (except for the pads of course) with green solder mask. The actual color of the interposer is probably brown to grey. It's applied essentially like a paint, then cured to a hard protective finish using UV (and selectively, so uncured parts can be washed away, revealing things like our LGA pads).

    The discoloration you're seeing is actually just where the solder mask got applied a little thicker than other spots. If you look in your second photo, the pattern looks just like where something was painted slightly unevenly.

    The contact pads are all almost exactly in the same plane as each other, so when you look at them from side angles, thicker solder mask between them will block your view of the gold pads more than thinner areas of solder mask. It only works if you're looking at it from an angle though. The pads look fine and the same color if you look head-on. But if you look from an angle, you're effectively putting part of the pads, which are ever so slightly recessed relative to the solder mask, in the shadow of that said mask. Thicker areas will cast a larger shadow/obscure more of pads nearby.

    If you examine the CPU pads for long enough, hopefully that description will start to make some sense. It's not the easiest thing to describe, at least for me.

    Regardless, its just a perfectly normal and purely cosmetic imperfection that will not have any effect on anything. I know it is hard to not really give a CPU like that a good eyeing-over, especially considering how expensive any LGA3647 CPU probably is, but none of these are totally perfect. You can always find something off depending on how hard you're willing to look. But all the things that would cause problems are actually things that are obviously going to cause problems in this case. Like a dried coffee drip on the gold pads, or a capacitor ripped off, or a cracked interposer.

    All I see in your photos is a perfectly happy, healthy CPU though. It's fine :).


    When I say ever so slightly, I mean it doesn't actually matter. Everything manufactured has tolerances, and as long as they fall within them, its fine. I don't really know what part of the manufacturing process causes it - if I had to guess though, I would
     
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  3. Jon

    Jon Member

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    Thanks for the explanation. The solder mask thickness would do that. It is the paintbrush effect that puzzled me a bit. For now this particular ES chip is reporting no memory on all channels so waiting on another one actually tested with the same X11SPM-TF rev1.01 and bios 2a I have. Cleaning the chip pads with alcool did not change that pattern was somewhat wondering is that was not something insulating?
     
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  4. 101

    101 New Member

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    The soldermask is generally the same thickness everywhere. What you are seeing is ground/power plane pours as well as routing affecting the transparency of the dielectric layers under the soldermask.
     
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