*2.4.1 Design for test*

*Design and Manufacturing*

and distributors).

failures (MTBF).

part numbers must be equal.)

• Regulatory compliance: RoHS/REACH.

• Screening: favor pre-screened or tested parts.

• Life span: favor parts with higher Shelf life.

• Economic order or lot quantity: Consider minimum buy.

• Bring the strategic suppliers on board the PPL project

nance), the possible savings in each phase are examined:

the company's PPL project.

enforce the practice of using a PPL.

• Lead-time: consider cost vs. the desired lead time trade-off.

• Accessibility: parts that can be purchased from multiple sources, (vendors or/

manufacturers' names and part numbers. (Different manufacturers' crossover

• Alternating source: same form, fit, and function for parts, but different

• Reliability figures: mean time to failures (MTTF) or mean time between

Considering the main stages in the product's life-cycle (from concept to mainte-

• Research and design: Excluding a newly introduced component's unknown performance will accelerate design validation and testing efforts. Shorter development cycles realized through less component failure issues and time taken for trouble-shooting and reworking breadboards and prototypes. Quicker proof-of-concept results. Parts used from PPL are more likely to be

• Purchasing: Material planning is more stable making part procurement less challenging. Strategic suppliers are encouraged if they is actively involved in

• Manufacturing: Less line failures using proven parts. Assembly personnel already very familiar with part handling requirements and issues.

• Customer Support: Fewer returns and higher reliability. Practice with frequently used parts promotes a deeper understanding of part behavior and common failure mode and symptom identification. Customer satisfaction with longer life product and fewer returns, and fast turn-around time in repair.

The design engineer who selects the components must choose as many parts as possible from the PPL. Ideally >80% of the bill-of-materials (BOM). By selecting even a majority of the parts from the PPL, the benefits realized from the arguments presented above should be sufficient to encourage the company to validate and

Finally, it is obvious that the PPL should be created and managed by the Industrial engineering people who are the stakeholders of the activity. In fact, PPL has a n impact on all phases of the product life-cycle. The size of PPL depends on the complexity of the typical system the company develops. For an aerospace

available, and small development quantities can be ready at-hand.

**14**

Design for test is a crucial aspect to guarantee the part can be efficiently produced during its life-cycle- The part must be designed so that it's key features and characteristics are accessible and verifiable during production test. Keep in mind that in the aerospace industry, practically 100% of the realized parts are fully tested, often over temperature and in mechanically stressful condition (vibration or similar), to verify they are fully compliant to specification and free from manufacturing defects. Moreover, the test is functional and not merely structural. Manufacturing functional tests are carried out to verify that the part is working and function as expected and not just assembled correctly. Functional test on 100% realized HW parts is typical of the aerospace industry to guarantee performance and reliability of manufactured parts and is less applicable to consumer products due to the very high time and cost involved in these kind of test. Finally, aerospace modules that fail the first manufacturing test need to be analyzed and tuned so the part meets the technical specification. Given the time and cost involved in the assembly process, it is illogical that the part should be discarded if the first production test fails. Consequently, designing parts for testability greatly aids the troubleshooting phase, ensuring production people can speedily identify the shortcoming and restore the part.

Given this scenario, it is mandatory that the design team keeps into account these aspects when designing the part. The principle is to add components and interfaces to make it easier to develop and apply manufacturing tests to the designed hardware. At the same time, test engineering department should be consulted in the design phase, so they can bring provide advice and most of all start designing the Automated Test Equipment (ATE) that will be used in production phase but could also be used by the engineering team for product verification and validation. The idea underlying design for test is: Pay less now and pay more later without DFT.
