2005 Articles

When considering whether to outsource rework operations, the quality of the rework needs to be ensured. An EMS provider or OEM can use several criteria to qualify the suitability of a contract rework and repair facility including the quality systems of the provider, training of their personnel, equipment used and material control system employed.

The facility should have a quality system with appropriate operating controls in place. ISO 9001:2000, ISO 14001 (medical) and MIL-I-45208 (military) are some of the accreditations that contractors should be registered to or be able to comply with. The vendor should be able to anticipate and prevent problems in the rework process by complying to the practices of the applicable standards for assembly (J-STD-001), rework (IPC-7711), repair (IPC-7721), moisture-sensitive device handling (J-STD-033) and inspection criteria (IPC-A-610). Systems should be in place to calibrate and maintain the equipment.

Rework and repair facilities and their customers need to agree on both procedural (generally IPC-7711 for rework and IPC-7721 for repair) and inspection (generally IPC-A-610) criteria. Each rework operator should be able to perform standard repair and rework operations such as repairing a lifted pad or removing and replacing an SOIC per IPC guidelines. In addition, where appropriate, the QC inspection staff at the contract facility should be able to demonstrate the ability to inspect the performed rework either per contractual requirements or applicable standards. Rework personnel should be trained in proper rework, repair and workmanship guidelines and have demonstrated the ability to properly handle electronics assemblies while maintaining ESD handling guidelines (per EOS/ESD 2020).

The contract facility should also have the equipment to ensure a high level of workmanship. This includes a variety of area array rework systems, from simple time and temperature control models to those with split vision capable of employing computer-controlled time-temperature profiles. These sophisticated systems permit the right level of profile control for the broad spectrum high-density large package area arrays requiring rework. A diverse set of reflow options including IR, convection hot air directed systems and reflow ovens will permit the rework provider to properly remove components without damaging or shifting nearby components. For board-level repair, precision mills and high-speed drills and routers should be available to fabricate the fixtures for rework and make precision populated board trace cuts (Figure 2) and routings. Also, QC tools should be on hand, including x-ray with void detection and a 120KV plus plate voltage for a variety of telecom, power and military boards, as well as endoscopes for determining the attachment characteristics of the ball to the device or the board (Figure 3). A digital camera-based optical inspection system is also useful for issues documentation.

FIGURE 2: Populated board trace cuts.

FIGURE 3: Endoscopic image of BGA.

For Pb-free rework, equipment should include a high-end area rework system that can control top-of-package-to-board temperature tolerances to 10°C; dedicated soldering fountains (to minimize potential cross-contamination of solders); board preheaters with Pb-free temperature capability (to minimize board warpage). Pb-free also means components will be more moisture-sensitive, thus requiring the rework facility to be able to bake, dry and seal parts.

Control of rework and repair materials and components is necessary to ensure a high level of quality. Contract rework and repair providers are nearly always provided with parts, boards and labels by the EMS or OEM. This requires that the material be logged and tracked with the job order. Material control of the fluxes and solders, generally provided by the contract rework provider, ensures consistent, high-quality workmanship. Solders should be properly stored with solder pastes refrigerated under monitored temperature conditions. PCB repair materials such as dry-film backed circuit frames, epoxy and hardeners and mask repair material need to be monitored for the proper shelf.

Pb-free materials require new levels of control. Soldering materials such as wire spools, bar and paste solders, and fluxes need to be controlled and quarantined for release against job orders. Job orders should be tagged to make sure the right solder alloy and materials are used. These materials should be controlled and only used with specific job orders. Material control is key to ensure RoHS compliance and reliable solder interconnects. PCB repair materials should also be RoHS compliant; for instance, make sure that a replacement circuit trace or pad is made from non-lead solder.

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