I don't tear down many consumer products (when they break, just throw them away) but it seems like COB (chip-on-board) construction isn't common any more. Did it go away, like cordwood?
John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics
It's going gangbusters in LED lighting applications. But it looks like it may be losing out to FlipChip in the emerging super-miniaturized and high density embedded systems, although it's still frequently used.
CAGR: Compound Annual Growth Rate
Right, LEDs are often wire-bonded to a pcb or to an aluminum thing with a thin white insulated coating.
Serious chips seem to be going to leadless packages and BGAs.
COBs don't look repairable to me, so a dense board might have bad yields with COB. Cordwood had the same problem.
We use some tiny unpackaged BGA GaN fets and glob-top them after assembly. We install them on small mouse-bite pcb subassemblies so we can replace them if a GaN fet fails.
I wonder what the first-pass yield is on cell phone boards, and if they are repaired or tossed.
AI Overview
Typical first-pass yield (FPY) for consumer electronics and standard PC board manufacturing generally ranges from 95% to 99% at individual steps or well-managed production lines. However, because smartphone circuit boards feature high component density, complex multi-step processes (component placement, reflow soldering, screen/housing assembly, and testing), the overall Rolled Throughput Yield (RTY) across all sequential operations is lower, often landing closer to 80% to 85% before rework.
John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics
In the distant past (approx 2005 - 2010), I helped maintain a few mountain top weather stations. Most of the hardware was cheap consumer grade products from La Crosse which used COB construction and phenolic PCB's:
"Teardown: Zapped weather station"
Notice the number stations and sensors that use COB construction:
Touch the epoxy blob and the IC wire bond breaks. Put it in a condensing atmosphere and water damage kills the chip after about a year. No conformal coating. Thermal cycle the COB, and the chip flakes off the PCB.
I haven't done anything with cheap consumer grade weather stations since Covid (about 2019). It's possible that La Crosse and Oregon Scientific have improved their acts, but I really don't know. My guess(tm) is that COB is slowly disappearing, but is not yet extinct.
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