tiny metal balls around PCB screw holes - Page 1
Forum section: electronics / general

author: coppercone2
author_rank: Super Contributor
timestamp: January 09, 2025, 11:27:15 pm
content: I have a gtx 1080 graphics card that I took apart and it seems like there is golden/copper colored balls lining the screw hole where you screw down the heatsink and other hardwareWhat is this called? is it some kind of feature for grip?https://tpucdn.com/gpu-specs/images/c/2951-pcb-front.jpgWhat is this texture/feature called and what is the exact purpose?bottom left its clear in the picture.Is that a soldered part, or they place those individually? it looks organizedIts not holes, it feels like someone soldered 'shot' to the PCB or something like that.I think mine were all gold plated but I don't want to take the card apart again.I thought they either solder on little features or have a part that is soldered on over the pad.and I wanna buy those too

author: jpanhalt
author_rank: Super Contributor
timestamp: January 10, 2025, 12:25:20 am
content: https://electronics.stackexchange.com/questions/313397/should-mounting-holes-have-solder-bumpsTwo supposedly flat surfaces may have poor contact. The balls, which are considerably softer than copper or plated copper, allow better contact as they deform more easily.

author: coppercone2
author_rank: Super Contributor
timestamp: January 10, 2025, 12:27:10 am
content: Oh damn, its solder. I was hoping it was something else. That is a can of wormI never searched for solder because there is no way I thought they would use solder.

author: thm_w
author_rank: Super Contributor
timestamp: January 10, 2025, 12:27:32 am
content: Discussed here:https://www.eevblog.com/forum/chat/solder-dots-around-mounting-hole-what-are-they-for/https://electronics.stackexchange.com/questions/240092/why-do-some-pcbs-put-vias-around-mechanical-through-holeshttps://electronics.stackexchange.com/questions/137394/mounting-hole-on-a-pcbhttps://electronics.stackexchange.com/questions/313397/should-mounting-holes-have-solder-bumps

author: coppercone2
author_rank: Super Contributor
timestamp: January 10, 2025, 12:32:48 am
content: When I took it apart, the screws were somewhat looser then I thought. But it is a creepy can of worm that they put on this graphics card.However, there is so many screws its like a RF can, so maybe whatever creep related problems there are its not a issue.I was hoping it was some special feature that would not lead to creep related discussion about solder.I guess because it has a high probability of going to a noob, the card is likely to die from being over tightened compared to issues caused by creep, so it works as a damage limiter.I wonder if the 5000 series cards have this lol. Because some pictures show bare copper pads like I expect.

author: thm_w
author_rank: Super Contributor
timestamp: January 10, 2025, 12:57:31 am
content: If its a flat screw head I can't see it helping with creep, could be worse if anything.If its a serrated head, it might help allow the head to bite into something instead of damaging the PCB.

author: coppercone2
author_rank: Super Contributor
timestamp: January 10, 2025, 12:58:43 am
content: I want to say most of them are flat cylinderical hex screws IIRC

author: Analog Kid
author_rank: Super Contributor
timestamp: January 10, 2025, 03:49:22 am
content: Quote from: thm_w on January 10, 2025, 12:57:31 amSorry to be a bit pedantic here, but this has always bothered me:You mean around-headscrew*, which has a flat bottom.Flat-head screws generally have tapered (cone-shaped) bottoms, unless you're referring to specialty screws like "cheese heads" which are flat on both top and bottom.It also bugs me when people conflate flat-head screws withslottedscrews, as opposed to Philips, Torx, etc. As in "hand me that flat-head screwdriver" when they're driving a round-head, slotted screw.That should properly be called aslottedscrewdriver.Now we'll have to see how my score compares to @TimFox's on the pedantry scale ...*Or fillister head, or pan head, or any number of other flat-bottomed screws.

author: jpanhalt
author_rank: Super Contributor
timestamp: January 10, 2025, 07:47:52 am
content: Head of the screw class:https://www.fastenersuperstore.com/fastener-guides/screws-head-styles?srsltid=AfmBOooVsbs-VtMlcF1M0hWuiwU1Hsb6BW19mgIMFFoQ_XsvTqMbTw1_On most electronic stuff I have seen, round heads are relatively uncommon. When there is a protruding head, it's usually one of the flatter head styles; although, one does occasionally see fillister styles. Once the head profile is defined, then you have to worry about defining the drive, e.g., Phillips, slot, hex, torx, Reed&Prince/Frearson, one-way (aka prison) ...

author: thm_w
author_rank: Super Contributor
timestamp: January 10, 2025, 09:23:43 pm
content: Quote from: Analog Kid on January 10, 2025, 03:49:22 amFlat bottom screw head yes.

author: Analog Kid
author_rank: Super Contributor
timestamp: January 10, 2025, 10:41:23 pm
content: Quote from: thm_w on January 10, 2025, 09:23:43 pmExcept that's not how they are identified. They're generally called by what's on top of the screw, not the bottom.Look at the screw-type chart that jpanhalt posted above. Very handy reference.

author: thm_w
author_rank: Super Contributor
timestamp: January 10, 2025, 10:59:06 pm
content: Quote from: Analog Kid on January 10, 2025, 10:41:23 pmI think you are missing the focus of this thread, I don't care about the screw type (philips/hex/whatever), that wasn't relevant to the discussion.What was relevant was the bottom portion of the screw that contacts the PCB and the shapes/features of that.As was demonstrated in the attached photo.Google search "PC case screw" and you'll see many are serrated.

author: Analog Kid
author_rank: Super Contributor
timestamp: January 10, 2025, 11:25:39 pm
content: I'm familiar with those. Thems are special-type screws, kind of with a built-in lockwasher.

author: jpanhalt
author_rank: Super Contributor
timestamp: January 11, 2025, 12:09:45 am
content: Quote from: thm_w on January 10, 2025, 10:59:06 pmYou seem to have missed the purpose of my post. Different head profiles have different contact areas. Truss and washer head have a lot of contact area. Pan has a bit less, round head and fillister are even less. The question posed was what are the bumps. That was answered. Then "why" transformed into area of contact. Undercut heads have a very specific purpose if you give just a little thought of how screws are made.If you really want to get irrelevant, let's talk about the difference between screws and bolts. You see both in electronics. Which would you use to attach a PCB to a project box versus , say, a ground wire to a PCB?

author: thm_w
author_rank: Super Contributor
timestamp: January 11, 2025, 01:01:56 am
content: Quote from: jpanhalt on January 11, 2025, 12:09:45 amI don't see where it transformed to area of contact but OK: presumably you want a wide enough area to reduce compression of the FR4.Here is another photo with screws in place:https://i.ebayimg.com/images/g/DD8AAOSwVaJjoiut/s-l1600.jpgplain but a little wide low profile screws there, no solder. There is a complete mix of with and without, even from nvidia themselves.The problem with solder I could see is creep: "That is, standard SnPb solder readily creeps at, and well below, room temperature."https://www.metallurgy.nist.gov/solder/clech/Sn-Pb_Creep.htmMaybe someone can compare FR4 with solder, I assume solder is worse but not sure?https://www.mdpi.com/1996-1944/11/11/2114

author: CatalinaWOW
author_rank: Super Contributor
timestamp: January 11, 2025, 07:28:16 am
content: Yes solder does creep. But except for a few weirdos like those of us on this forum there is no concern about this because the whole board will be obsolete and discarded in a couple of years. Also the boards only have to pass EMI/EMC tests when new, so if the primary purpose of these screws is to connect the case to ground no one will notice they have failed. Or a failure will trigger purchase of a replacement piece of gear making the manufacturer happy.Just recognize that if you, like me and many others on this forum want to keep your treasured old electronic goodies working like new you will have to snug up the screws periodically (maybe even schedule it for every other year). Or just recognize that this is mostly a belt and suspenders issue and things will work fine in most cases.

author: Analog Kid
author_rank: Super Contributor
timestamp: January 11, 2025, 07:54:50 pm
content: Small data point here: I tend to have, and use, many older adapter cards in my computahs, some of them two decades old.I've never had a failure on any of them while in service, and many (most?) of them have those kinds of ground connections with serrated-bottom screws and some kind of receptive pad on the PCB. So I don't think this is a major source of failure.

author: coppercone2
author_rank: Super Contributor
timestamp: January 11, 2025, 08:17:22 pm
content: the balls are new to cards I never saw that before

author: mikerj
author_rank: Super Contributor
timestamp: January 11, 2025, 09:37:09 pm
content: Quote from: coppercone2 on January 11, 2025, 08:17:22 pmThis is very common on computer and other equipment, though sometimes they are segments rather than dots. Just search for pictures of motherboards, you'll struggle to find one that don't have this feature.

author: thm_w
author_rank: Super Contributor
timestamp: January 13, 2025, 10:02:55 pm
content: Quote from: mikerj on January 11, 2025, 09:37:09 pmYes most motherboards use them, but, most motherboards are OSP. You won't get good connectivity with OSP forever so its kind of a necessity to use solder bumps there:https://www.raypcb.com/pcb-osp-surface-finish/GPUs are a bit more flash, and need ENIG for the fingers anyway, so they might do the whole board as ENIG. With ENIG there would be no connectivity reason for solder bumps. Though it may add some protection when over torquing and damaging nearby traces, as mentioned.