What is Rolled Throughput Yield? A Complete Guide

Rolled throughput yield is an important quality metric that measures the percentage of units that make it through a process without any defects Unlike traditional yield metrics that focus on individual process steps, rolled throughput yield provides a holistic view of process quality by considering the cumulative effect of defects across multiple process steps

In this comprehensive guide we will cover everything you need to know about rolled throughput yield including

• What is Rolled Throughput Yield
• How to Calculate Rolled Throughput Yield
• Rolled Throughput Yield vs. First Pass Yield
• Why Rolled Throughput Yield Matters
• How to Improve Rolled Throughput Yield
• Best Practices for Using Rolled Throughput Yield

Let’s get started!

What is Rolled Throughput Yield?

Rolled throughput yield (RTY) measures the probability that a unit will be produced without any defects across all production processes. It is calculated by multiplying the individual yield percentages at each stage of production.

For example, if a process has four steps with the following yields:

• Step 1: 95%
• Step 2: 90%
• Step 3: 85%
• Step 4: 80%

The rolled throughput yield would be:

0.95 x 0.90 x 0.85 x 0.80 = 0.612 or 61.2%

This means that only 61.2% of units, on average, will make it through this four-step process without any defects.

Rolled throughput yield provides a more realistic view of process performance than looking at individual step yields alone. High yields at each step do not guarantee high quality if defects are accumulating along the way.

How to Calculate Rolled Throughput Yield

The rolled throughput yield formula is simple:

Rolled Throughput Yield = Yield 1 x Yield 2 x … x Yield N

Where N is the total number of process steps.

To calculate it:

1. Identify the key process steps
2. Determine the first pass yield at each step
3. Multiply the first pass yields together

First pass yield is the percentage of units passing a step on the first attempt, prior to any rework.

For example, if 100 units go through Step 1 and 85 pass while 15 fail and require rework, the first pass yield for Step 1 is 85%.

Make sure to use the first pass yields in the rolled throughput yield calculation, not the overall step yields.

Let’s look at an example for a 5 step process:

• Step 1 Yield: 90%
• Step 2 Yield: 95%
• Step 3 Yield: 85%
• Step 4 Yield: 80%
• Step 5 Yield: 90%

Rolled Throughput Yield = 0.90 x 0.95 x 0.85 x 0.80 x 0.90 = 0.56 or 56%

While the yields for individual steps look decent, only 56% of units are making it through the entire process without any issues.

Rolled Throughput Yield vs. First Pass Yield

Rolled throughput yield is often confused with first pass yield. While they sound similar, there are some key differences:

• First pass yield measures the yield at a single step in the process.
• Rolled throughput yield measures the cumulative yield across multiple steps in the process.

First pass yield is limited because it does not account for defects introduced in later steps. A unit could pass first time at Step 1 but still fail at Step 3. This would count positively towards first pass yield but negatively towards rolled throughput yield.

Rolled throughput yield provides a more holistic view of process health by capturing the compounding impact of defects across all steps. It quantifies the true percentage of good units coming off the line.

Why Rolled Throughput Yield Matters

There are several reasons why rolled throughput yield is such an important metric:

1. Identifies hidden factory “waste” – Processes with high step yields but low rolled throughput yield are essentially creating scrap and rework “waste” that is going undetected. The cumulative defect rate gets masked by rework loops. RTY shines a light on this issue.

2. Drives proactive improvement – By exposing waste, RTY motivates organizations to make improvements before defective units get too far downstream. It promotes stabilization and defect prevention rather than reactive containment.

3. Enables data-driven decision making – RTY yields actionable data to identify problem steps and prioritize improvement efforts on biggest opportunities. Resources can be optimized to maximize overall equipment effectiveness.

4. Allows benchmarking – Unlike step yields, RTY can be benchmarked across different processes and plants. It provides an “apples to apples” comparison of true process capability. Best practices can be identified and replicated.

5. Supports customer satisfaction – High RTY translates to less finished product inspection, scrap, and rework. This results in more consistent on-time delivery and higher customer satisfaction.

6. Impacts profitability – Defects drive up costs due to yield loss, rework labor, material, testing, and delayed shipments. Maximizing RTY minimizes these costs and can significantly improve profit margins.

For all these reasons, understanding and optimizing rolled throughput yield is key for any operation looking to improve quality, reduce costs, and better satisfy customers.

How to Improve Rolled Throughput Yield

Here are six approaches to improve your process rolled throughput yield:

1. Address lowest first pass yield steps first – Focus improvement projects on steps with the lowest first pass yields as those have an outsized impact on overall RTY. Solve the biggest issues first.

2. Perform root cause analysis – Analyze process data to identify the most common defect types and root causes. Address these at the source rather than relying on inspection and rework.

3. Optimize preventive maintenance – Many defects originate from equipment issues like tool wear, misalignment, fouling, etc. Enhance PM plans to better prevent breakdowns.

4. Standardize procedures – Lack of standardized work and operator-to-operator variability drives defects. Document best practices and train employees.

5. Improve incoming part quality – Supplier defects are amplified across downstream processes. Implement supplier quality programs and controls.

6. Automate processes – Manual and semi-manual processes are less consistent. Automating can eliminate operator-induced defects.

It’s also important to have disciplined closed-loop corrective action processes when defects do occur so issues are contained, addressed at the root cause, and prevented from recurring.

Best Practices for Using Rolled Throughput Yield

To get the most value from rolled throughput yield, keep these best practices in mind:

• Track regularly – Monthly or quarterly is usually frequent enough. Avoid tracking daily or weekly as normal variation can obscure trends.

• Compare over time – Look at historical trends to see progress. Short term fluctuations are normal but the goal is an upwards trajectory.

• Segment by product and process – Calculate separately for different products, processes, lines, plants, etc. to identify areas for targeted improvement.

• Set goals – Define a rolled throughput yield target to drive continuous improvement behaviour. Make sure goals are realistic yet challenging.

• Communicate results – Share RTY openly across shifts, functions, and levels. Transparency helps engage everyone in improvement initiatives.

• Link to financials – Connect the dots to product costs, scrap expense, rework hours, etc. so that impact is clear.

• Reward and recognize – When RTY goals are met, celebrate wins with the team! And if targets are missed, focus on learning not blaming.

Key Takeaways

• Rolled throughput yield (RTY) measures the percentage of good units from start to finish of a multi-step process.

• It captures the cumulative impact of defects across process steps rather than just looking at individual step yields.

• RTY is calculated by multiplying the first pass yield percentages at each step together.

• High RTY requires stabilizing processes and preventing defects at the source rather than relying on containment and rework.

• Monitoring and optimizing rolled throughput yield improves quality, productivity, cost, and delivery performance.

By mastering rolled throughput yield as a key process metric, organizations can drive systemic improvements in operational excellence. While it takes diligence and teamwork to get RTY levels up, the long-term rewards are well worth the effort.