Replaced part affecting service life?

[VinceTech]

Hi

A new ME equipment manufactured in 2015 has service life of 10 years. A year later (2016), PCB was damaged. A spare part PCB manufactured in 2010 replaced the damaged PCB.

My question is:
1. If the PCB service life is 10 years too, should be service life of the equipment after replacing the PCB become 5 years. How should manufacturer specify this.
2. If any suggestion/requirement in spare parts manufacturer, so that the service life of the equipment will not be affected after replacement of a part.

Thanks,

 

[Ronen E]

Are you asking from a regulatory perspective, warranty perspective, or otherwise?

From a regulatory perspective it depends how you define things. My advice is to be as clear and as explicit as you can in your definitions. For example, if you define that the allocated service life begins when a part starts being actually used (i.e. installed and activated), it doesn't matter when it was made (at least as long as its design is still current). However, shelf life might be an issue. It depends on the nature of the part (or the device), what potential ageing mechanisms are there, are they time dependent (i.e. does anything decay/deplete/deteriorate etc. over time regardless of actual use) and so on.

 

[yodon]

Agree with @Ronen E but let me add that service life is just the period you indicate in which the device will meet specification. There may be service / repair activities in there that don't affect the advertised service life. As @Ronen E noted, there may be factors that affect the ability to meet spec in which case you either define the service life within that period or you establish a service schedule to ensure continuity.

I had one client that tried to argue that the "service life" was indefinite since, with scheduled service and repair, the system would meet spec 'forever.' This was not acceptable to the Notified Body who required that a specific timeframe be cited. It's kind of a wonky requirement (to have to specify), IMO. How does one define the service life for software for example? In my world, it seems to frequently boil down to market viability life.

 

[Miner]

For example, if you define that the allocated service life begins when a part starts being actually used (i.e. installed and activated), it doesn't matter when it was made (at least as long as its design is still current). However, shelf life might be an issue. It depends on the nature of the part (or the device), what potential ageing mechanisms are there, are they time dependent (i.e. does anything decay/deplete/deteriorate etc. over time regardless of actual use) and so on.

I am speaking strictly from a product reliability perspective, not regulatory.

Ronen makes a very important point here. Some product will not appreciably age/wear while in storage. However, some do. Tires are an example of the latter. The rubber in a tire begins to deteriorate as soon as it comes out of the mold. A 5 year old tire that has never been installed on a vehicle is end of life and should not be used.

With a PCBA, corrosion while in storage is a potential risk. If the PCBA was sealed in a anti-static bag, corrosion is probably fairly low risk. If not sealed, you would need to consider the environment (e.g., temperature, humidity, corrosive gases, etc.). Another potential issue might arise if electrolytic capacitors were used. These have the potential for the electrolyte drying out under higher temperatures. A less likely, but possible issue is damage from shock and vibration. In other words, perform a risk analysis before deciding.

 

[VinceTech]

It seems that a shelf life for the PCB before assembly shall be determined. Without control of the raw material shelf life, the service life of the equipment can be assured.

Has anyone had similar experience in control of raw material for ensuring the service life of equipment? How was it done? Thanks

 

[Ronen E]

"Control of raw material" is very general. It depends what "materials" (products?) you are referring to.

 

[VinceTech]

"Control of raw material" is very general. It depends what "materials" (products?) you are referring to.

Thanks, Ronen

For example PCB. We have PCB manufactured and stored in house. Customer/3rd party service organization can purchase the PCB for replacement. Do you think we need ensure the PCB sold is able to assure 10 year service life from the date it was shipped out? This means we have to ensure the date of manufacturing PCB is not too old (e.g. already in store for 5 years) as some capacitors can only have life of 10 years.

 

[Ronen E]

Thanks, Ronen

For example PCB. We have PCB manufactured and stored in house. Customer/3rd party service organization can purchase the PCB for replacement. Do you think we need ensure the PCB sold is able to assure 10 year service life from the date it was shipped out? This means we have to ensure the date of manufacturing PCB is not too old (e.g. already in store for 5 years) as some capacitors can only have life of 10 years.

With specific regard to PCBs, this is outside my technical expertise. You need to conduct a careful technical analysis, identify the risks and address them.
More generally, it's a matter of stock management, stock rotation etc. Obviously you need to implement measures to ensure spare parts are dispatched such that technical claims (e.g. effective service life) and contractual obligations can be met.

 

[Peter Selvey]

"Service life" should be seen as a regulatory point of view, which is the period of time which the device is safe to use. It is declared in risk management file. During the service life faults, breakdown or trouble can occur, but they should not place the patient in any immediate danger. Most devices have protection against faults and abnormal situations, so the critical point is making sure these are reliable for the "service life". So for example if your replacement PCB has safety critical circuits (e.g. over-temperature protection) then it might be prudent not to use 5 year old PCBs. I would also question the compatibility, for example if the design has changed is the old PCB compatible with the newer design?

Apart from this it is just a business decision. Equipment fails from time to time, it is to be expected. But if your failure rates start to rise above normal levels (which could be due to poor stock management of replacement parts) then you get a bad reputation. Sales go down and the business dies. So you want to make sure your 5 year old PCBs do not cause any trouble.