Wednesday, June 27, 2012 | Sjef van Gastel, Assembléon Netherlands B.V.
A single key requirement, ultra-repeatable assembly, dominates medical electronics production. While obvious for pacemakers and other implantable devices, it is essential for wearable devices like hearing aids, too. Poorly performing products can lead to instant rejection from users, leading them to prefer their original, bulky, but reliable, devices. Older patients particularly have difficulty coming to terms with new technology and can have little tolerance for a new device if it doesn’t work properly the first time out of the box. Repeatability is also critical for equipment like MRI scanners. Many diseases need early treatment and patients cannot afford the delays introduced by an expensive machine lying idle because a component on one of the boards was poorly soldered.
Quality and repeatability can’t be inspected in products. These features must be designed in, which involves working on each part of the process to reduce variation. That, incidentally, also reduces costs. In every step of the manufacturing process, detecting a defect costs 10x more than the previous step. Costly automated optical inspection (AOI) and test equipment can filter out defects as early as possible, but, even then, at least 10% of defects still go undetected. Figures from various industries show that over 60% of returned products were subject to earlier rework. And, as miniaturization progresses, rework is often no longer an option and that significantly increases scrap costs.
Medical production also has to be flexible to keep pace with regular high-mix product changes. Production needs traceability and effective enterprise resource planning (ERP) software to integrate management information throughout the organization. Most importantly, though, medical production must give a first-pass yield of virtually 100%. That means optimizing each of the three major surface-mount processes shown in Figure 1: Stencil printing, pick-and-place, and reflow soldering (the best solder technique for high-density electronics production).
Figure 1: Process requirements for each of the three major SMT process steps.