The importance of through hole plating - Page 1
Forum section: electronics / general

author: AndyC_772
author_rank: Super Contributor
timestamp: October 06, 2015, 01:06:14 pm
content: Today I finally got round to fixing the display on my old Yamaha DSP-A1.The amp is built like a tank and was top of the line in its day, but it suffers from an endemic fault with the display. First a few pixels go out, and over time, it becomes more and more unreliable until eventually the display goes completely blank. They all do it, it's not a problem unique to my particular unit.The attached photo shows why.Every singlejoint on that row of the DIL display module looks like this, with a 360 degree annular fracture around the pin, and about half the joints on the other row are broken too. The rest of the board is perfectly OK, it's just the display module itself that's affected.For reasons best known to Yamaha, the holes in the PCB for the display aren't plated through, so each solder joint is bridging a free space gap between the pin and the pad. It's clearly deliberate; every trace leading to the display is on the solder side of the board.I'm assuming the fractures are caused by thermal expansion, though I'm struggling to figure out the balance of forces that would break all the joints rather than just move the entire display by a fraction of a mm.If anyone has experience of this phenomenon elsewhere, I'd be interested to hear about it. Yamaha amps seem particularly prone to it, which is odd given the otherwise excellent build quality.

author: krivx
author_rank: Frequent Contributor
timestamp: October 06, 2015, 01:31:20 pm
content: This is a mid to late 90s product? It may have been designed (or used design rules) for construction with lead solder but manufactured with brittle lead-free. If those joints need to be heated to a higher temperature to reflow then that might be your answer.

author: nctnico
author_rank: Super Contributor
timestamp: October 06, 2015, 04:36:02 pm
content: I have seen this lots of times in computer monitors. Often around the HV transformer and other power semiconductors.

author: coppice
author_rank: Super Contributor
timestamp: October 06, 2015, 04:57:07 pm
content: Philips TVs and audio went through a phase of being notorious for this in the 70s. I guess they make the holes loose to assist rapid insertion of the parts, but it makes for a big gap bridged by nothing but solder. Not a recipe for high reliability.

author: tggzzz
author_rank: Super Contributor
timestamp: October 06, 2015, 05:10:51 pm
content: Quote from: AndyC_772 on October 06, 2015, 01:06:14 pmhttps://www.eevblog.com/forum/blog/eevblog-804-hp1740a-oscilloscope-repair-part-2/msg771062/#msg771062

author: langwadt
author_rank: Super Contributor
timestamp: October 06, 2015, 05:24:12 pm
content: Quote from: krivx on October 06, 2015, 01:31:20 pmI've seen it happen to almost anywhere there is a mechanical load on a solder joint, led or no lead

author: krivx
author_rank: Frequent Contributor
timestamp: October 06, 2015, 06:22:17 pm
content: Quote from: langwadt on October 06, 2015, 05:24:12 pmSo have I, but this is a display module. It shouldn't have any mechanical stress.

author: wblock
author_rank: Regular Contributor
timestamp: October 06, 2015, 06:55:41 pm
content: Think of the stress of repeated heating and cooling cycles. The solder is, hopefully, smooth and continuous around the pin, but the pin is a different metal with a different coefficient of thermal expansion.

author: John Coloccia
author_rank: Super Contributor
timestamp: October 07, 2015, 12:05:07 am
content: I'm not familiar with how that thing is built mechanically, but often what happens is they get build on a line and then stuffed in the box...and then everything gets bolted down. If that's the case, there's bound to be constant stress on that joint because nothing is perfect.I have board mounted stuff on my products, but when I build it I bolt everything together in a representative enclosure (a prototype, a scratch and dent I can't use, etc...), and THEN I solder it up. When it goes into the real box, everything is perfectly aligned and there's minimal stress.Does the display have a sturdy bracket that's also soldered to the board? That helps a lot, but it's often times absent for whatever reason ($$$). I'd be surprised if it didn't have that.Anyhow, anything that has any weight to it will generate mechanical stress, even just moving it around.