Testing and Rework

Bed of nails. The subassembly is placed on a dedicated test fixture and held in place by a vacuum or mechanical means. Probes access key electrical traces on the subassembly to check individual devices. Through a technique known as hackdriving, the inputs of each device are isolated from the associated circuitry and the component is tested for functionality. This type of testing is expensive and is only practical for high-volume subassembly qualification testing and rework. 

Over time, a wide assortment of packages has been developed to house components. Selecting the correct package type for each component is one of the most important parts of the design process. Package types chosen affect ease of design, assembly, test, and rework, as well as prodnct cost and component availabUity. 

This requirement can impose unnecessary constraints if you take it literally. Many activities in quality plans and procedures are performed to give early warning of nonconformities. This is in order to avoid the losses that can be incurred if failure occurs in later tests and inspections. The earlier you confirm conformance the less costly any rework will be. 

State laws, corporate policies, insurance regulations, and any other appropriate mandates should be considered when establishing regular testing cycles. Additionally, any SRV that pops or discharges a corrosive or tar-like fluid should be removed and reworked as soon as the discharge is detected. 

As previously stated in Chapter 10, testing should be designed to detect errors in the developed computer system. If the testing process itself is not robust, that, too, will induce errors and rework. The testing conducted on 85 computer systems used across primary and secondary pharmaceutical manufacturing in several companies is analyzed here to examine test failures and how they were managed to closure. 

Written procedures for the receipt, holding, testing, and disposition of returned APIs and intermediates should be established and followed. These procedures should provide for the identification and holding of relumed APIs and intermediates. Where an API or intermediate is placed back into inventory, the reason for its return should not have been due to quality issues, and the integrity of the returned materials should have been verified. If the quality or purity of the API or intermediate cannot be ensured, the returned materials should be destroyed, reprocessed, or reworked as appropriate. If the reason for the return implicates associated batches, an appropriate investigation should be conducted as described in Section XII.F.4. 

All reprocessing and reworking must come to the attention of the quality unit for final review and approval. Continuous reprocessing to bring a batch into conformance should not be allowed, as it indicates that there is something unusual and unknown about the process and/or the quality of the product. The need for additional or new tests must be... 

When the intended aim is to change a formula, reduce costs or duplicate a formula, an evaluation is sought. Holistic tests (with same-different or triangular tests) can be used in the context of a similarity-based approach (beta risk). In practice, these tests can certainly be implemented, but at project team level they are impossible to manage because of insufficient participants. Rework of products is also difficult, because these tests do not provide any information on how products differ. We have therefore formalized an approach that can evaluate proximity between tests and a reference product. 

A wide range of methods has evolved for attaching components to PCBs. The methods chosen as well as the combinations of methods chosen for a product have a substantial impact on the final cost, ease of assembly, availability of components, ease of test, and ease of rework. The five basic attachment combinations are through-hole only, through-hole mixed with surface-mount on one side, surface-mount one side only, surface-mount both sides, and surface-mount both sides with through-hole. 

The metrics of assembly trade-offs relates factors of process, component selection, and test to assembly prices. Yields and rework are factored into the points of the Assembly Report Card. The point total provides an estimation of the relative prices of assembly and test. 

Thermal Stress Solder Float Test Soldering temperatures expose PCBs to thermal and mechanical stress and may deform the PCB shape and cause premature degradation of the base material. Thermal stress inspection is performed to predict the acceptability of the PCBs after the assembly and rework process. FIH degradation, separation of platings or conductors, and base material delamination are induced or amplified by the thermal stress test. The PCB specimen is oven-conditioned to reduce moisture, placed in a dessicator on a ceramic plate to cool, fluxed, floated in a solder bath, and placed on an insulator to cool. Visual inspection for imperfections is followed by microsectioning of the PTHs and inspection under a microscope for integrity. Test coupons are typically used for thermal stress inspection. 

Semipermanent connections have been required for rework, replacement of components and modules, and repeated connections. Realistic assembly processes for most electronic prodncts are not perfect, so semipermanent terminations are required for rework and replacement of electronic components or modules in standard assembly processes to increase final manufacturing yields. Also, temporary connections are required for testing and adjusting electronic products and modules. These often need 5 to 10 reconnections, with as many as 100 reconnections required in extreme cases. Basic data on typical semipermanent termination technologies are summarized in Tables 64.6 through 64.8. 

Quahty control iaspection is a post-, or at best concurrent, manufacture activity. The QC laboratory reports on ia-process and finished product quahty based on testing. Thus QC confirms whether a material has been manufactured in conformance. Sometimes QC also assists the production unit in salvaging process material or reworking off-standard finished product. 

Some tolled products can be reworked if they fail quality assurance tests. In these cases the production cost may go up, but the product is not a complete loss. However, other tolled products, some pharmaceuticals for example, could be completely ruined by similar processing mishaps. Losses in these cases can be quite extensive. Test runs and approved rework procedures for such products may help avoid these losses. 

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