water splash caused minor iPad Power Button problems, what is the risk of mainboard corrosion? Summary


Water splash on iPad Pro 12.9" (first generation)
Power button stopped working, then few times appeared to press itself, then started working again.
Third party repair service refused to open it and clean the mainboard to prevent corrosion.


Detailed explanation and questions are later, but basically I'm not sure if it's better to keep insisting and searching for other repair service to clean motherboard or maybe the risk is negligible?

Details

I have a waterproof backpack but I must have not zip it completely in a hurry and I was caught by heavy rain.

Upper part of my iPad got slightly wet (about 5cm from the top, based on trace left on protective case). It was not submerged in the water, it appears to be a splash type effect.

I haven't even noticed that after arriving in my office, I was working on it as usual and suddenly noticed the power button is not working and then suddenly noticed the water stain on the protective cover.

As emergency solution I enabled the accessibility feature as replacement for it.

Few hours later the button started to act like pressing itself, just few times, randomly.

Few more hours later it started to work back as usual.

After hours I went to nearest electronic repair shop which is trusted by couple of my friends. I requested them to open up my iPad and clean up the area around the power button using isopropyl alcohol to prevent corossion.

They refused to do it, they said it's just water and my iPad is going to be fine. Honestly, it sounds to me like they just didn't wanted to do it and gave me a bad advice. 

Some research

As explained in this reference, the rain water is not pure, it contains contaminants from the atmosphere and even after dried out, can cause corrosion and oxidation.

http://www.circuitnet.com/experts/80616.html

I also reviewed all the water damage related questions on this Stack and extracted relevant ones.

Answers that recommend cleaning at third party repair shops. However in case of those questions, device was submerged or there was large spill making most of the liquid enter insides of the device, not just splashed.

How to deal with phone dropped in water
MacBook Pro mid-2010- water damaged - but it still plays the chime?

Those answer recommend drying, ventilation and just using it as long as possible, however here there was a serious spill and most of liquid ended up inside of the device, in my case probably only a little bit, there is not much cavity to let water through on top of iPad case.

Spilled water on Macbook Pro 13 inch, early 2015
No sound (speakers/jack) + microphone&#39;s dead after spilling water

This one in addition seems very optimistic if amounts of water are small.

A few drops of water on my Macbook Pro

The answer here recommends ultrasonic cleaner, however I suppose it also requires opening up the device so doesn't make the repair less risky.

iPhone 4S fell into water and blacked out, with only CPU and mainboard burning. Is it possible to export the data from two years ago?

Questions

Potential damage could be worse than just power button replacement?

Given the fact the device was not submerged, only partially exposed to stream of water and visibly affected only the power button

If potential corrosion occurs, would it require only power button replacement or entire iPad mainboard?

Better to find another repair shop and insist for cleaning?

Cleaning the motherboard is a complicated repair, my iPad is 12,9" version, screen is easy to break, I don't feel confident doing it myself. I head iPads are designed to be splash resistant, I'm wondering if it is worth taking the risk and just not do anything or is it sure corrosion might get it and I absolutely need to search for new repair shop that will take the challenge and clean up the motherboard?

What if they offer this ultrasonic cleaning instead of isopropyl approach? Should I go for it?
I've been to one more repair shop, they also refused to open it and redirected me to official Apple Service center. I scheduled an appointment at the Genius Bar.

Apple representative provided me with following information:


They don't open iPads. Assuming you have Apple Care and there is a problem, they replace the whole unit.
They don't advise opening it, they say the device is sealed and glued and it would be hard to put it back together as it was.
They say they understand my concern about corrosion, after my requested, they showed me more or less where motherboard and batteries are placed.


I returned home and did more research on my own.


I checked settings of my iPad and got it's exact model: A1584
I Googled "A1584 teardown"
On this website I found very detailed photos of the inside. I grabbed the case my iPad had on during splash - it still had the mark after the splash. 
I downloaded the x-ray photo and highlighted the pattern of the splash on it, I also highlighted where mainboard is placed and with arrows I marked potential entry points of water.
I estimate, since the device was not submerged, only trace amounts of liquid could enter inside of the case and I think it's reasonable to say it couldn't reach the battery or mainboard.
I estimate worst case scenario, potential corrosion could damage the the smaller circuit boards connecting power button, camera and volume buttons to the mainboard.


Reference on iPad teardown

My decision:

Taking into account following information:


Device was not submerged and I estimate liquid couldn't reach critical components.
Device is sealed and non-trivial to open, after closing it again might become less hermetic.


I decide to


Not open it for cleaning of the motherboard.
Prepare extra means of precaution for such events, purchased a case with better sealing.