Circuit Board Fabricators

CBF has hired you to help determine why they are not able to produce the 1,000 boards per day.

1. What type of process flow structure is CBF using?

The company is using a batch shop process flow structure. CBF, Inc. bases its board fabrication process on the average job size or on its typical order. This means that the company proceeds with the manufacturing process in batches so as to meet the specific requirements per order. The typical contract that the company currently gets is 60 boards per order. However, due to persisting factory defects, they manufacture a total of 75 boards per batch in order to compensate for 20% of the boards that they typically reject during the process.

2. Diagram the process in a manner similar to exhibit 6.7.

According to the book, the diagram is an operation and route sheet that specifies operations and process routing for a particular part. It conveys such information as the type of equipment, tooling and operations required to complete the particular part.

The "Setup Hr." is derived from dividing the setup (minutes per job, as illustrated in exhibit 6.9) by 60 minutes. Likewise, the hourly capacity of each operation (Rate Pc. Hr.) is solved by dividing 60 minutes by the run (minutes per part, as shown in exhibit 6.9).

3. Analyze the capacity of the process.

The first thing to consider is the process of cleaning and coating of the boards. This particular process involves the set-up of the machines, the loading of the boards, and the actual cleaning and coating of the said boards by the machines.

From the computations above, it is clearly illustrated that there is a disparity between the loading of the boards into the machines and the output of the cleaning and the coating machines. The loading rate exceeds that of the cleaning and coating capacities.

There are 5 exposure machines, with a person attending to each one's operation, loading and unloading. This exposure machine involves a set up time, as illustrated below.

Again, the capacity of the exposure machine, which is 1,138 board, exceeds its preceding process, which only churns out 900 boards per shift.

In this part of the manufacturing process, a person is in charge of loading the boards into the machine. From the previous computation (in the part of coating and cleaning), the average loading rate per day is 1,019.

It can be seen here that the developing capacity of the machine far exceeds the number of boards that are loaded into it. Again, there is disparity between the processes.

Two people are stationed at the inspection part of the process where each board is picked from the conveyor as it comes from the developer. Moreover, the inspection machine optically checks the boards.

The inspection can go through 120 boards per hour. However, this is the part in the process where rejects are picked out. Historically, 15% of those that go through inspection do not pass. This means that out of the 120 boards that are churned out of inspection in an hour, 18 of them are did not pass. Therefore, in a full shift which ideally would inspect 1,800 boards, only 1,530 boards will make it to the next process, which is baking. The capacity of the bake oven is computed below.

If 1,530 boards passed the inspection and are passed on to the bake oven, only 1,365 of them are accomplished. Again, there is a deficit in capacity of the bake oven as compared to its preceding process output.

After baking, the boards are manually unloaded and placed on the cart to be moved to the drilling machines. Before drilling, there is a set-up required, and the capacity of this process is computed as follows.

The drilling machine can well accommodate the number of boards that are transferred to it because it exceeds the capacity of its precedent, which is baking.

After drilling, the boards are transferred for copper plating. Each board is manually loaded on a conveyor that passes through the plating bath. Likewise, there is set-up time involved before the boards are copper plated. This process has a lower capacity than the drilling machine.

The circuit board fabrication comes to an end after the copper plating. The boards are subjected to a final electrical test to check the integrity of the circuits. Another 5% of the boards are found to be defective during this stage. Before the tests are done, a setup is needed. The capacity for final testing is computed as follows.

Overall, there is an apparent disparity between the capacities of each of the operation processes. The output from the different stages ranges from 900 to as much as 1,800 boards. It is seen that the bottleneck in the whole manufacturing of circuit boards is in the part that has the lowest capacity, and incidentally, located in the earliest part of the production process - the cleaning and coating machines. This means that the maximum number of circuit boards that will be finished by the end of the day is 900. From the finished boards, there is a historical defect rate of 20%, thereby leaving a total of only 720 boards that are ready for packing and shipping to the customer. It is therefore apparent that CBF is manufacturing very inefficiently, as they 280 circuit boards short of the required output per shift of 1,000 units.

4. What is the impact of losses in the process in Inspection and Final Test?

It is said in the case that "due to the losses in the system", CBF created a policy to increase the size of an order to give way to rejected boards. The company has to make allowances in production because there may be problems in the process, which cause some boards to be deemed rejects.

On the average, 15% of the boards are typically rejected during inspection, and another 5% during the final testing. This translates to a total of 20% rejection/defect rate that happens in the whole process. In other words, for every 10 boards manufactured, 2 are scrapped out.

In order to meet the average order size, at least 120% of the orders should be started into the manufacturing process because along the way, 20% of those that went into production get rejected. In the case, an average job size is 60 boards. This means that fabrication should start with at least