I was trying to replace a larger memory size for my e-reader by re-balling, and I accidently knocked off the caps / resistors highlighted in red.

Do I need to replace these? Or can I ignore?

If I have to replace, how can I identify the types and farads etc.

 

Can you ignore them? No.
If the manufacturer of the board could have ignored them then they would have done so.

What values to use as replacements?
Your guess is as good as mine. You need to find the circuit diagram or reverse engineer the board and figure out the function of the missing components.

Or you can locate an identical board. You would have to remove the components in question and measure their values while they are off the board.

 

I've no idea what they do, but in these days of producing something for the lowest possible price, it's a pretty safe bet that they wouldn't have put something on that board unless it was absolutely necessary.

 

Can you ignore them? No.
If the manufacturer of the board could have ignored them then they would have done so.

Ive read many times over the years especially in laptop repair circles, that these tiny capacitors/resistors most times do not make difference when left off or left broken.

I havnt attempted to turn the device on since, would it be likely ok to turn it on and test if it works?

I've no idea what they do, but in these days of producing something for the lowest possible price, it's a pretty safe bet that they wouldn't have put something on that board unless it was absolutely necessary.

The difference in price between putting 5x 0402 caps and 7x 0402 would be negligible.

 

The difference in price between putting 5x 0402 caps and 7x 0402 would be negligible.

Have you ever designed anything for large quantity production?

 

Have you ever designed anything?

Everything in the circuit has a purpose. Some loss of functionality may not be immediately apparent.

 

Everything in the circuit has a purpose. Some loss of functionality may not be immediately apparent.

They may be decoupling capacitors. Loss of functionality may be hard to spot. A few extra errors here and there, random crashes etc.

 

The difference in price between putting 5x 0402 caps and 7x 0402 would be negligible.

Per unit yes... per 10,000,000 units that's a loss of profit

 

Have you ever designed anything for large quantity production?

Per unit yes... per 10,000,000 units that's a loss of profit

As you buy large quantity, prices come down further still.

aliexpress returns 10,000 0402s for $9, putting 3 extra 0402s per device(even if extraneous) would be immeasurable from a profit point of view.

 

Everything in the circuit has a purpose. Some loss of functionality may not be immediately apparent.

Ofc it does, but the question is can the device work safely without them.
There are multiple other components, some put in just to meet FCC laws, some superficial, etc.

 

Powered on the device, it works fine so far.

 

If I have to replace, how can I identify the types and farads etc.

If you still have the caps, you can measure their values.

Ive read many times over the years especially in laptop repair circles, that these tiny capacitors/resistors most times do not make difference when left off or left broken.

Those people don't know what they're talking about. Manufacturers won't waste money on unnecessary components.

The difference in price between putting 5x 0402 caps and 7x 0402 would be negligible.

Manufacturers still won't waste money on unnecessary components.

Powered on the device, it works fine so far.

The problem is that you can't test for worst case switching problems. It might work most of the time, but the first time that it doesn't could give you grief.

It took me many months to figure out that a bad memory board in one of my laptop (9 years old) was causing it to not boot. I was fortunate that the failure prevented booting 90+% of the time. It has booted consistently after removing the bad memory board. Which reminds me that I need to contact the manufacturer for a replacement (lifetime warranty).

 

As you buy large quantity, prices come down further still.

aliexpress returns 10,000 0402s for $9, putting 3 extra 0402s per device(even if extraneous) would be immeasurable from a profit point of view.

Personally I wouldn't by 10,000 of anything from aliexpress. 10,000 from a site I would buy them from is between 3 to 10 cents each depending on capacitance.

No matter what you think a penny is a penny and a dollar is a dollar. If they can save it they will. The shareholders expect it, the designers aren't going to add extra parts just to add complexity and more work to qualify the design, and profit is profit no matter how minute you think it is.

Edit:

Just because this is a stupid argument in the first place and I should have kept out of it...

It's not just the cost of the capacitors, but also the cost of the glue to set them in place, the solder used to solder them, and the time to place them. Consider a board that takes 60 seconds to place all the components minus the capacitors in question, but takes 61 seconds to add in the additional capacitors. In a 24 hour period that is the difference of 34 units. Using $59.99 I found for an Amazon fire and assuming a 100% markup that would put the factory price at $29.995. The difference of 34 units in a days time is $1,019.83... in a week $7,138.81... in a year $372,274.45.

Yes these are essentially made up numbers and I may be way high... or even way low. At the end of the day those four "meaningless" capacitors could equal the annual salary of the plant manager and maybe even first assistant.