why dont apple manufacture iphones/mac with cob,if dont want people fix them?

[aqarwaen]

why dont apple just manufacture iphones/macbooks with cob,if apple dont want people fix them?
I am not expert...but  if  i understand correct cob(chip on board) would render all repair attempts nearly imposible + would save some manufacture cost on large scale.
and with this i mean every single chip on iphone/mac board would deliberately be cob,to prevent people repair themself or make it near impossible.

so why dont apple and other manufacturers wont do it?whats reason why apple,samsung and ohters big electronic manufacturers dont use it?

[helius]

The simple reason is that there are much more important design criteria than the goal of frustrating repair, which it has never really been proven that they do.
COB is a method of connecting a bare die to a board using bond wires. It is used on cheap electronics to save the cost of chip packaging. What is wrong with COB?
1. Since it connects bond wires from the top of the die to the board, the pads must be outside the die footprint. This is a total obstacle to dense PCBAs like on today's cellphones and computers. Additionally, the number of I/Os on the die itself is limited by wire bonding. More I/Os are possible with flip chips and especially with multilevel packages.
2. Chips are tested in two stages: first, a wafer test does a very brief functional check over all dice prior to singulation. The bad dice are marked with a paint dot and thrown away, the good dice are packaged. After packaging, testing can be more intensive and identify chips with different performance levels (binning) as well as defects that cause reliability issues (margining). This intensive testing cannot be done for COBs, so they would cause failure rate of PCBA to increase.
3. Epoxy blob doesn't have such good thermal performance as you can get with integrated heat slug packages.

[tooki]

Apple doesn’t go out of its way to frustrate repairs; they just don’t prioritize third party repairability.

Anyhow, IIRC they’re using stacked SOCs and stacked PCBs. I don’t think you can do this with COB. Additionally, COB is used for devices without too many leads. But the SOCs have far too many pins, meaning that you’d need a ton of PCB space to put all the leads at the periphery of the SOC. This would frustrate the goal of compactness. They already use chip-scale packaging for some ICs, where the BGA has no actual package, and the balls are simply attached to the die. (Is this called flip chip? I forget.)

[helius]

CSPs are flipped, but the term flip chip (among its other meanings) is currently used for die-down packages using solder bumps and interposers. CSP is the same if you delete the interposer and just put the bumps down against the PCB.

[amyk]

Stop giving them ideas...

CSP is effectively COB without the epoxy.

If they wanted to make it nearly impossible to repair they could've done it already even with regular components --- just pot the whole thing and weld the case shut.