Electronic Assembly Design FMEA (DFMEA)

T

twobits

#1
Hi,

I’ve been asked by my boss to implement a FMEA review into a new design. The product is an electronic assembly consisting of 4 Circuit Card Assemblies (some based on old designs, some are new), a back plane and housing. I’ve compiled a review scoring sheet but I’m currently not sure of the best way of carrying out the FMEA. My queries are:-
1. Do I carry out a FMEA against each sub-assembly or just the completed product
2. When carrying out the FMEA, does each individual component have to be reviewed for failure modes? Some circuit cards have up to 2000 components, although majority are resistors and capacitors. Or can we split the circuit card up to functions and address the failure modes of that circuit function.
3. Does any one have any examples of a FMEA for an electronic assembly please

Any comments or guidance will be gratefully appreciated. Thank you
 
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Stijloor

Staff member
Super Moderator
#2
Hi,

I’ve been asked by my boss to implement a FMEA review into a new design. The product is an electronic assembly consisting of 4 Circuit Card Assemblies (some based on old designs, some are new), a back plane and housing. I’ve compiled a review scoring sheet but I’m currently not sure of the best way of carrying out the FMEA. My queries are:-
1. Do I carry out a FMEA against each sub-assembly or just the completed product
Welcome to The Cove Forums! :bigwave: :bigwave:

You can start with a System FMEA followed by Sub-system FMEA's.

2. When carrying out the FMEA, does each individual component have to be reviewed for failure modes? Some circuit cards have up to 2000 components, although majority are resistors and capacitors. Or can we split the circuit card up to functions and address the failure modes of that circuit function.
You can perform Component FMEA for families of components.

3. Does any one have any examples of a FMEA for an electronic assembly please?
Search the "Post Attachment List" here at The Cove Forums.

Any comments or guidance will be gratefully appreciated. Thank you
 
M

manuuee

#3
I was searching for the example of FMEA analysis but i couldn't found it...and i didn't found the Post Attachment List indicated into the topic.
Can you help me?
Thanks a lot!
 
M

Murphys Law

#5
If I was you, I would make it as modular as possible: Do a DFMEA on the product (You are a bit late in the development process to be doing it IMO) and a PFMEA on the manufacturing process.

For the PFMEA, I recommend to split it into each manufacturing step and do a sub-PFMEA on each process step. If you have a control plan, use that as your basis for assessing the process steps.

One thing is a true FMEA should a team effort. It should not be produced by Quality alone. Quality can facilitate it but the FMEA should be owned by a functional owner. For example, a process engineer. You should also involve manufacturing personnel as they best know their processes and failure modes.

For a Design FMEA, in my world we run two levels of DFMEA: A technology level FMEA that goes across products and then a local product DFMEA that addresses items local to the new design not addressed in the technology FMEA.

We tend to produce DFMEAs for Automotive devices. For commercial devices, we do a "risk assessment" which is essentially a cut down FMEA without the cumbersome quirks of a true DFMEA. We use Excel to do this. For your application, you may want split this into your respective modules/piece parts or do it by categories such as Supplier / board assembly / System mount/ Test.

For our manufacturing processes, we do PFMEA regardless of whether it is an ISO or TS16949 line. The PFMEAs are now pretty much in sustaining mode run by the factories.
 
Z

Zbigniew Huber

#6
Hi,

I?ve been asked by my boss to implement a FMEA review into a new design. The product is an electronic assembly consisting of 4 Circuit Card Assemblies (some based on old designs, some are new), a back plane and housing. I?ve compiled a review scoring sheet but I?m currently not sure of the best way of carrying out the FMEA. My queries are:-
1. Do I carry out a FMEA against each sub-assembly or just the completed product
2. When carrying out the FMEA, does each individual component have to be reviewed for failure modes? Some circuit cards have up to 2000 components, although majority are resistors and capacitors. Or can we split the circuit card up to functions and address the failure modes of that circuit function.
3. Does any one have any examples of a FMEA for an electronic assembly please

Any comments or guidance will be gratefully appreciated. Thank you
Hi.

Ad.1.
It depends. If your team designed entire system (including cards) then yes.

Ad.2.
IMHO ? it is not necessary to go down into each part individually. It may be treated as ?blocks? (like power supply circuit, blocking capacitors circuits etc.) Split into functions.

Ad.3.
I do not have such DFEMA in English - sorry.


I suggest:

1.
Prepare System-FMEA (SFMEA) first (top level D-FEMA of the entire system with housing, backplane and cards. The cards and backplane are ?sub-systems? of your system.

2.
Prepare boundary diagram with major blocks (cards, housing, cables, backplane, connections to external systems, environment influence, operator/user interactions

3.
Use Interface matrix to identify relationships between each sub-systems and between subsystems and environment and user.

4.
For each item (sub-system) define functions (what the subsystem should do/provide/ensure/prevent. Take ideas form:
- customer requirements
- legal requirements
- manufacturability requirements
- industry standards like IPC-2221
- requirements form "interfaces" between sub-subsystems (from interface matrix).
- customer usage


When functions are defined then define failure modes (as non-fulfillment of functions) and continue with rest of the DFMEA columns.

For SFMEA the cause of the failure will be a ?sub-system? failure or environment or user misuse. Example:
- Function: Maintain data transfer at temperature ranges 0C-70C
- Failure: Data corruption at elevated temperatures
- Cause1: Temperature inside the unit above 70C due to fans failure (subsystem failure).
- Cause2: Operator covered the fans with foreign objects (user misuse)

As next step:
For each card and backplane ? prepare ?sub-system DFEMA? where card failures (failure modes) listed as causes in SFMEA have own causes where sub-circuits or discrete components failures are identified as causes.


Note that for DFMEA you should focus on ?design related causes? like ?part with lower power rating SPECIFIED etc. Consider manufacturing process as correct.

Best Regards,
Zbigniew
 
S

SmallBizDave

#7
I've been successful doing FMEAs on complex products by defining the target failure modes by starting strictly from the specifications. Typically we'll have less than, say, 50 specifications for a product that might have multiple circuit cards and thousands of components. This helps focus the FMEA on things the customer cares about.

We look at each spec and consider the various ways the product might be caused to go out of that spec. Those become the failure modes to look into. While this is a system level FMEA it is not uncommon for the investigation to delve down to the subassembly level pretty quickly, so I don't know that it's realistic to define it as a system level or subassy FMEA necessarily. It accomplishes the mission.
 
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