Figure of Merit: A Way to Score Your Opinions
Metrics are data, and statistically backed measures. It is always expedient to base decisions on data and metrics. But what if a metric doesn’t exist? Then you can create the next best measure: the Figure of Merit.
The problem with opinions is that they are difficult to defend, and when used in conjunction with producibility, they often they vary from person to person. That is why the Figure of Merit process is so popular. For a small amount of work by experts it produces a scoring procedure that can be used and understood by all.
Metrics also establish a common language that links manufacturing to design. The "producibility scores" form an unbiased basis that allows a team an approach that results in quality, cost competitive products.
The strategy in applying these measures is shown in Figures 1. The process of analysis is unique to every individual and company, but certain conditions have to be met and considered if the product is going to be successful. If the score meets producibility requirements, then select this approach. If not, evaluate other opportunities and repeat the process.
Creating A Figure of Merit
Metrics can take many months to develop, and the amount of experimentation may make them costly. One measure that is much more cost-effective and quicker to develop is the Figure of Merit. The Figure of Merit is the result of one or two days’ work by a group of design and manufacturing experts. The process is a nine-step procedure as follows:
- Definition of New Measure (FOM)
- Why Selected
- Survey Customers for Needs and Expectations
- Brainstorm factors
- Sort ideas into groups
- Create group header definitions
- Prioritize groups
- Construct Factor Weighting Value Tables:
- Create Linear Model for FOM
This procedure uses classical Total Quality Management (TQM) techniques to brainstorm, rank and formulate an equation that will score producibility, assemblability or any other measure that can be used to do design planning. The two factors used in the producibility score are made up of the 1. COEFFICIENT- CN and the 2. Factor Weighting- FWN
1. Definition Objective of New Measure
Define or identify the new measure to be developed. What property of a product would gain you the most competitive advantage? Manufacturability, DfM, Reparability, Serviceability, Testability, Reliability, Low Cost or Rapid Time-to-Market.
2. Why Selected
Ensure that there is relevance to improved performance and communication if this FOM is developed. Are they part of this Team? How does the new FOM improve the product?
3. Survey Customers for Needs and Expectations
Who are the intended users of this FOM? Identify their NEEDS and EXPECTATIONS. Collect data by surveys, interviews, or brainstorming of contributing characteristics or variables.
4. Brainstorm Factors
Collect a team of ‘experts’ that have a vested ownership of this new FOM. Invest in a “Facilitator” to keep the activities rolling and on schedule. Give everyone plenty of cards or ‘Post-its’, then go around the team and collect “ideas’ of what is important for this new Measure of FOM. Allow plenty of time! If the ideas stop coming, take a break and resume. Have the Facilitator PUSH for “one more idea”. There are no discussions or arguments during the Brainstorming-just ideas. Randomly lay out the cards so that all the team members can see them. Take as much room as it needs. See Figure 2.
5. Sort ideas into Groups
The purpose of this step is to collect the ideas that go with each other. In silence, all team members should simultaneously begin moving the idea cards, collecting and arranging in columns the cards that each person believes belong together. All the cards should remain visible during this process so that everyone can consider the arrangement as it emerges. If cards are redundant, overlap them, but in such a way that both can be read. Team members should freely change cards between groupings or create new groupings as they feel appropriate. Team members are allowed to disagree with a placement by making a new placement or returning to a previous one. Back and forth moves may occur for some time until the team settles on an arrangement that is acceptable to everyone. Some cards (ideas) may be loners that do not seem to fit in any grouping. They should be left that way rather than try to force-fit in any grouping. The Facilitator helps resolve conflicts about ideas by changing their definition or creating a new Group. See Figure 2.
6. Create header card for each Group
The Facilitator works with the Team to create a ‘header’ or ‘definition’ for each Group which captures the essential link among all the ideas in that Group, and consists of enough words to clearly convey the meaning. Look for one idea that ties the whole group together. In many cases that central idea will not exist yet on a card. If it does not, the team should decide on a central idea and create a concise, usually three to five words. See Figure 2 and Figure 3.
7. Prioritize and Rank Each Group
The Team needs to prioritize and rank each of the groups created by the last two steps (5 & 6). Three methods can be used:
Mulitvote: each member of the Team is given a fixed number of votes (usually the number of groups divided by 3) to cast to the groups he/she thinks is the most important.
Ranking Vectors: arrange each group in circular layout and connect and connect by arrows as to which affects the other. Count the arrow-starts to give scores.
Paired Ranking: This is the method I prefer. It simplifies the choices for voting and is the easiest to interpret. This is seen in Figure 4. Each Group is listed in the horizontal and vertical axis. A diagonal line is drawn. Discussion and voting are performed on each pair; 1-2, 1-3, 1-4, 1-5, then 2-3 (already did 2-1), 2-4, 2-5, then 3-4, 3-5 and finally 4-5. Which group wins get a “ PLUS +”, ties get 0 and losers get “NEGATVE –“. The +, 0 and – are placed in opposite on the other side of the diagonal.
Coefficient-CN: The coefficients in the producibility score are the result of the prioritization process (Step 7). The actual voting scores of ‘wins+’ form the coefficients, Cn. In Figure 5, that is; 1 has 2 wins, 2 has 3 wins, 4 has no with and is dropped (coefficient of 0) and 5 has 2 wins.
8.Construct Factor Weighting (FW) Table
Each factor that emerges from the ranking process is calibrated by assigning values from one (1) to one hundred (100). The "1" factor are "easy to manufacture" and the "100" factor are impossible today but merely very difficult in a few years. In my example, the measure is “minimum drill diameter size” and values are assigned for 1-25-50-75 and 100. The Factor Weighted is used to calibrate the ‘measured’ group from 1 to 100.
9.Create Linear Model for FOM
The resulting scoring equation will look like the linear equation below (sum of CnFWn) and would be used like this:&
SCORE = (C1) (FW1) + (C2) (FW2) + (C3) (FW3) + (Cn) (FWn) +
For example, if we assume the producibility of a bare PWB may be scored with the above equation if the following factors were established by the F.O.M. Process :
1. Size of the substrate C1 = 1.5
2. Number of drilled holes C2 = 3.0
3. Minimum trace width C3 = 4.0
Where the proposed PWB design has:
1. Size of the substrate FW1 = 36
2. Number of drilled holes FW2 = 18
3. Minimum trace width FW3 = 31
The producibility SCORE would equal : 232 = 54 + 54 +124 = 1.5 x 36 + 3.0 x 18 + 4.0 x 31
As I sometimes tell people about the process, “It’s based on expert opinions, used over and over, but it is surprisingly ACCURATE!
Would you like to find out more about how Altium can help you with your next PCB design? Talk to an expert at Altium.