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Relationship between PFMEA & Control Plan for Special Characteristics

Discussion in 'FMEA - Failure Modes and Effects Analysis' started by Pongsakorn, Jun 1, 2016.

  1. Pongsakorn

    Pongsakorn Active Member

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    I need someone to enlighten me regarding the relationship between PFMEA & Control Plan in term of "Special Characteristics". I might be confused on this since my understanding is as follows:
    - "Special Characteristic" defined in "Classification" column of PFMEA refer to Failure Mode.
    - "Special Characteristic" defined in the "Special Char Class" refer to the characteristice to be controlled taken from "Current Process Control (Prevention/Detection)" of PFMEA.

    As such, I do not see any linkage between PFMEA adn Control Plan, I am now having problem in explaining customer on how to develop Control Plan from PFMEA.

    If anyone has a good example of PFMEA containing special characteristic and related Control Plan, please
    share to me so that I can clearly see and know how do I transfer Special Characteristic from PFMEA to be in Control Plan.

    Thanks for reading this post and your help
     
  2. Miner

    Miner Moderator Staff Member

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    Per the AIAG FMEA Manual, the Classification column is dual purpose. It may be used to:
    1. ...highlight high priority failure modes or causes that may require additional engineering assessment.
    2. ...classify any special product or process characteristics... ...that may require additional process controls.
    In the context of item 2, there is definitely direct linkage to the control plan for both product characteristics and process parameters.
     
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  3. ncwalker

    ncwalker Well-Known Member

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    When our suppliers submit to us the Process Flow Diagram, the PFMEA, and the Control Plan, one of our checks before we approve the PPAP is that the special characteristics are annotated as such on all three documents. In the PFMEA and Control Plan there is a column that is usually checked. They typical way they complete this is they annotate this column with OUR marks for the special characteristics we have designated on the design documentation. And they also mark the column with THEIR marks if they have identified something that may not be important to us, but could be important to them. Then we look that the OP numbers match from the control plan back into the PFMEA and back into the process flow diagram. On the process flow diagram it is a bit unstructured as to how they choose to mark the special characteristics because it is less common, but we still require it.

    Some key points: If the special characteristic is generated in several steps, usually the last step is the only one marked to avoid confusion. Example: I have a tightly toleranced inside diameter that I have marked as an SC. You drill the hole on OP10 then you ream the hole to final size on OP20. You would only mark OP20, even though OP10 contributed to the hole.

    Also, while an SC marking typically bumps the "Severity" score on the PFMEA, it does not necessarily mean "Detection" and "Occurrence" get bumped as well.
     
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  4. MCW8888

    MCW8888 Well-Known Member

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    "SC" is generally interpreted as Special Characteristic, which is a feature of the product which requires special process controls, which are Key Control Characteristics. For each SC there should be a corresponding Control in the CP.
    If you have a Process Flow Diagram with 10 OP's there should also have a corresponding 10 OP's in the PFMEA and in the Control Plan.
     
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  5. Pongsakorn

    Pongsakorn Active Member

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    Really thanks for your reply.
    I originally understood as what you mentioned in item 2 but when I actually did the FMEA and Control Plan, it cannot be done so.
    As an Example (BTW, I work in Semiconductor Company), at Wire Bonding Process the Failure Mode is Lifted Ball Bond, if we put "SC" for this failure, then
    determine the detection by 1) Perform Visual Inspection 2) Perform Wire Pull Test, so the Visual Inspection and Wire Pull Test will the product characteristics to be controlled. With this scenario, please advise where "SC" should be indicated in the Control Plan.
    If you have any good example to illustrate this, kindly share me.
     
  6. MCW8888

    MCW8888 Well-Known Member

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    I would not put any "SC" symbol in the CP but I will have "Wire Bonding" as a step.
     
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  7. Pongsakorn

    Pongsakorn Active Member

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    Thanks for the reply.
    If there is no "SC" defined in the Control Plan, it will be deviation to the ISO/TS 16949 para 7.3.2.3 requirement as shown below.
    upload_2016-6-2_14-52-32.png
     
  8. Golfman25

    Golfman25 Well-Known Member

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    I wouldn't read it like that. It can't logically force you to have special characteristics. You have to identify any special characteristics. There may or may not be any. If you do identify them, then you have to include them in your control plan.

    It seems that for years we did process flow, femas, and control plans without incident. Then all of a sudden our "wording" was wrong. These processes and documents are supposed to be helpful for your organization, not points of endless discussions of semantics and confusions. Good luck.
     
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  9. ncwalker

    ncwalker Well-Known Member

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    And here is the difficulty with the tabular layout of the PFMEA and CP. I am unclear as to the layout of the two inspections (Visual and Pull Test) as I don't know the industry. But for the purposes of the illustration, let's assume that Visual is done by the operator at the OP on the line, and Pull Test is done in an audit fashion later. Let's also assume there are 5 OPs: OP10 to OP50 and this Visual is done in process on OP30, while the Pull Test is done off line. A roving inspector does it later by taking a sampling of boards to a lab where the pull test machine is located. Without ALL the details your control plan OPs could go
    10 Do this
    20 Do that
    30 Bond the ball?
    40 Something else
    50 Last step

    Now this OP30 has our critical "Bond the ball" step. And the check is visual. Probably not going to look good on the RPN. Even if you add:

    60 Roving Inspection (Pull test goes in here)

    Upon review of the OP30 it's going to look weak (initially, until someone grasps the entire control plan and realizes there is an ADDITIONAL step of inspecting it later). What you want to do is eliminate this.

    Option 1: If the roving inspection is checking various things generated by ALL the OPs, some people sprinkle in the inspection as sub steps. Like:
    10 Do this
    15 Inspect this
    20 Do that
    25 Inspect that

    But that's misleading. Unless the inspections truly ARE done piecemeal, in between the OPs, then it is appropriate. You should be able to put a sticker on a piece, and the order of "touches" to the piece should match the control plan. So if the roving inspection with pull test is truly last, it needs to be:
    60 Roving Inspection and Pull Test

    Now, where do you put the SC mark? At a minimum, it needs to be located at the last point where it was CREATED. You want to know where it was MADE in the process. Now if this is at OP30 then put it there. And if OP30 looks like a weak control (Visual always looks weak) and at the end of the process you have added a layer either by an end of line test OR a statistically sound periodic inspection, you CAN put in the "Action Plan" section of OP30 something line "Refer to OP60 for additional checks of this SC."

    Alternately, you could put the SC anywhere it was mentioned. Let's say OP10 does some prep work, and OP60 inspects it. You could mark all three (10, 30, and 60) with the SC. There's no rule against this. I personally find it very confusing. I want to look at the print, count up all the SC marks and find the same number of SC marks on the PFD, the PFMEA and the CP. So my preference is that they go on the last OP that is involved in making, not measuring, the SC.

    There is a truism in that part of this actually IS a bit of a game. The real goal of the control plan is as the blue books state. But the auxiliary goal is structure it in such a way that your customer representative likes it AND can easily follow it. There is a human nature problem sometimes with being "wrong." Here is what I mean:

    You hand me this control plan and it's a little unclear. So I say "Your RPN stinks on this OP30 ...." And you say back to me "No, no, it's OK, see later on? We have additional controls." Well, you're going to make me feel like a dummy for not seeing it. So, I have to save a little face and prove to you that I am NOT a dummy. So what am I going to do? Start digging .... You want to avoid that at all costs. And let's be clear, I do NOT mean to advocate dishonesty or trickery, I am advocating clarity and organization. If your control plan is like that, I won't get all up in your business on a witch hunt. :)

    Oh. And STOP merging all the vertical rows in Excel. When you scroll around, it makes it glitchy and jumpy looking on the screen. It's frustrating and makes me want to dig. :)
     
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  10. Pongsakorn

    Pongsakorn Active Member

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    Thanks for your reply. I interface with many customers / auditors, I experienced different understanding and comment. I have ever thought that I understood FMEA clearly but not for today since there are many different input causing confusion. Anyway, I am trying to settle this with all of your worthwhile inputs. Really thanks.
     
  11. Pongsakorn

    Pongsakorn Active Member

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    Thanks for your reply.
    Visual Inspection and Wire Pull Test are out in the "Product Characteristics" column in the Control Plan. That' why I see that the "SC" in "FMEA" refer to Failure Mode but "SC" in "Control Plan" refer to "Product/Process Characteristics" taken from "Current Control" column in FMEA. This is my main confusion.
    The correct example of FMEA and Control Plan could help me. I am finding out but still not yet discover.
     

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