First pass yield

Thus, it is no surprise that commercialization results are far from optimal. University research that could be converted to useful products is done not at all or done imperfectly. In a process sense, the latter stages of the development process can have very low first-pass yield. Consider as well the education process. Due to the lack of experiential understanding of the reality of the business world, students can emerge from the process essentially poorly educated. For example, as a result, those entrepreneurial graduates who start their own companies are prone to make mistakes—not just unavoidable mistakes but mistakes that could have been avoided. 

Base stock consistency control is the secret to first pass yield, i.e., meeting finished product specification limits with the specified blend of base stocks. Most finished shortenings physical characteristics are controlled with solids fat index (SFI) iodine value (IV), and/or a melting point analysis. However, time restraints during hydrogenation do not allow the long elapsed times required for these results. More rapid techniques to control base stock end points are ... 

The direct amination of olefins (hydroamination cf. Section 2.7) has only been achieved efficiently for alkenes with a tertiary carbon atom (e.g., isobutene) or ethylene [6]. Furthermore, the equilibrium of the hydroamination is not favorable in many cases, so first-pass yields can be low with a need for a high recycle stream. 

For each process, estimates of process capability and yield for critical processes should be summarized and reported (baseline). Based on overall business objectives, realistic and attainable objectives for process capability and first pass yield should be set. 

First-Pass Yield. The first-pass yield equation derives from the Wiebel probability failure equations. Equation 19.12 is of a more general form of the equation typically used to predict ASIC yields by defect density. 

To determine the constants A and B in Eq. 19.12, a fabricator will need to characterize their manufacturing process. Selecting a number of printed circuits currently being produced that have various complexity indexes does this, ideally some low, medium, and high. The first-pass yield (at electrical test without repair) of these printed circuits for several production runs is recorded. Any statistical software program that has a model-based regression analysis can now determine A and B from the model (Eq. 19.13). 

The first-pass yield will follow the examples in Eig. 19.14. Constant A determines the slope of the inflection of the yield curve, whereas constant B determines the x-axis point of the inflection. 

FIGURE 19.14 Estimated first-pass yield as a function of PWB design complexity. 

Yield Calculation Steps. To calculate the first-pass yield coefficients, there are six steps ... 

Collect the first-pass yield information for these selected boards, at least 10 runs (see Table 19.5). 

P/N Run First pass yield (at Electrical test) Average... 

PWB Complexity. Figure 19.14 shows this company s first-pass yield. The curve with A = 11.5 and B = 9.0 was current for six months. Price index is the total points from the complexity matrix divided by the first-pass yield. 

PWB Fabrication Example. Let s continue with the consumer electronics board example from Sec. 19.4.5.Table 19.9 lists the initial design characteristics of the printed circuit and the resultant total design points. Table 19.10 shows the calculation of the complexity index, estimated first-pass yield, and resultant price index and price adjustment. 

Rolled throughput yield (RTY) It is also known first pass yield (FPY). It is the ratio of the number of completely defects free without any kind of rework during the process units at the end of a process and the total number of units at the start of a process. The theoretical throughput rate is often regarded as the number of units at the start of the process. RTY/FPY is used as a key performance indicator to measure overall process effectiveness. 

The supplier must demonstrate that the capacity of the process meets DaimlerChrysler s requirements. This includes measuring first-pass yield at various steps of the process. 

Product quality is usually determined and certified off-line in a quality control laboratory to ensure that specified properties of a production batch fall within the established range. Specifications related to molecular weight, charge density, composition, particle size, viscosity, rate of dissolution, solution viscosity, and residual monomer are common. Production batches that do not meet the specifications either require further processing, rework, or disposal and reduce production efficiency. As online analytical methods are employed, first pass yields (the proportion of production that meets specifications the first time) usually increase. 

The coverage of a FR by (sub-)products shall be above an appropriate threshold in order to determine them as appropriate reusable (sub-)products with some certainty. With respect to this coverage, Suh recommends to calculate the entropy as introduced by Shannon. In K-RAMP, the theoretical possible first pass yield (FPY) with a range between 0 and 100 % is used to determine how much the members of Pz and therefore the derived handling instraction of the new process segment would cover the specification range If the theoretical FPY is above a certain threshold the existing subproduct can be considered for reuse. 

The old saying, You can t inspect quality in, remains true. Defect prevention is essential, and it starts with a well-defined process quality plan that reduces process variation. This plan must outline the methods used to monitor products and processes during production. Processes must be stable and repeatable before they can be measured. Critical processes must be continuously monitored and analyzed to determine if it they are achieving the desired quality targets. When problems are detected countermeasures should be employed immediately. First pass yield and DPMO are essential quality metrics. 

The first pass yield metric reveals (in percent) the number of boards that make it through all of the assembly processes without failing. First pass yield is the number of acceptable boards (x) divided by the number of inspected boards (n), or fpy = x/n. 

Several long-term studies show a 50% reduction in all categories of defects, which in some cases translated into a 5-7% gain in first-pass yield. Benefits due to nitrogen inerting depend on the activity of the paste, where the milder the flux activity of a paste is, the greater are the benefits that are realized. Fine-pitch boards show a markedly higher improvement in defects than coarse-pitch boards [7,8]. 

---