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Inspection Machine Capability


Inspection Machine Capability | 7 May, 2001

Automatic optical inspection machine suppliers seem to tailor their machines for different tasks [eg, paste inspection, component ID & positioning, reflowed solder quality]. Is this observation accurate? If not, why? If so, what characteristics of the different types of inspection machines make them suited to the different tasks?

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Inspection Machine Capability | 8 May, 2001

The AOI suppliers are not tailoring the systems to the application but are defining the applicability of their system to a specific AOI segment �i.e. �leveraging� the limitation of the technology. Would a AOI supplier possess a technology that will allow the acquisition of 3D information in real time � say equivalent to 50 � 60 sq cm / sec.- and at a sufficient resolution � say 15 micro-meters/reading all AOI applications will be equal performed by an identical system .

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Inspection Machine Capability | 9 May, 2001

Yes, your observation is accurate. Different process steps have different inspection requirements which necessitates employing different imaging technology to ensure the best performance (detection and throughput). Orbotech, for example, offers both 2D- or 3D-based AOI systems depending on the inspection step and inspection requirements.

In general, it's easiest to divide the in-line inspection tasks in SMT lines into two types: pre-reflow and post-reflow, or even refer to it as prevention and detection. Pre-reflow inspection bares with it more measurement and placement accuracy reporting, while post- reflow inspection primarily deals with fault detection. For example, in the placement stage, an in-line AOI system "sees" each and every element on the board and can measure and identify an evolving drift or trend before a defect has actually occurred. While the drift and trends may not actually lead to the creation of a defect at the post-reflow stage because the oven may "correct" the component position during soldering, the data gained from the post-placement inspection is an important indicator for process control and prevention. Likewise, the exact measuring of the component at the post- reflow, although maybe important in some cases, is practically less useful.

While post-placement inspection can employ 2D imaging to detect and measure the correct placement of components, the post-solder AOI system must use 3D imaging to deal with the 3D properties of the elements on the board due to the type of defects and process faults, such as bad solder joints, that must be found at this stage.

The post-paste stage is a special case in which 2D imaging is used to check for the detection of 2D defects types such as: twisted, missing, smeared, offset, bridging and pad coverage, while a volumetric measurement is needed for the paste volume measurement.

So, to summarize, if you want the highest performance at a given inspection step, you should choose the relevant solution designed for that step. You may also choose to have your AOI tool to be able to deal both with the measurement challenges of pre-reflow and the 3D detection challenges of post-solder. As we do not live in an ideal world, and budgetary constraints are playing an important role, you should look a vendor that can offer flexible solutions and the capability to field retrofit your system per your changing inspection stages and needs. This maximizes value of your investment.

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