Written by Charl Roux
Since X-ray was discovered in 1895 by W.C. Roentqen – (he called it “X”-ray because the ray’s nature was unknown at first), X-ray technology in the electronic manufacturing environment has taken a huge leap forward providing a new way of doing process and quality control. It has added an incredible increase in confidence and quality assurance to manufacturing processes.
Parsec utilizes its X-ray machine to rectify process deficiencies right at the start of a production run. Without an X-ray machine, manufacturers have to rely on normal visual inspection methods, trusting that their manufacturing processes are in order. There is however no guarantee that mishaps will not occur with the resulting rework and repair guaranteed to eat into profits which in today’s competitive environment may already be very marginal. If potential deficiencies are detected at the first-off inspection stage, adjustments can be made prior to the start of a large production run of thousands of boards.
Besides the visual evaluation of a first-off board assembly, functional testing is necessary to determine if the assembly is meeting the design specification. However, none of these methods can provide an indication of long term reliability.
Environmental stress screening may be applied at a later stage of production to reveal reliability problems; but by this time it may be too late. With the aid of X-ray, many defect or process indicator opportunities can be inspected. Apart from the common issues such as bridging, Ball Grid Array (BGA) voiding, dry joints, open circuits, missing balls on BGAs and misalignment issues, the less common and subtle issues such as pop-corning, BGA co-planarity problems, incomplete reflow, BGA ball size variation, solder balling, wetting, THD hole fill, secondary reflow, fillet lifting/tearing in lead-free joints, tomb stoning, via plating, wire bonds and “grey” components can be observed. In the case of reworked BGAs, there can never be 100% confidence that a reworked BGA has been fitted correctly unless an X-ray machine is put to the job.
In a recent production run, we were able to identify a batch of “grey” components before the production button was pressed, by doing a simple first-off PCB assembly process check with X-ray inspection. Since Parsec was not contracted for functional testing of these boards and a batch of 12,500 boards was on order, the impact of building these boards without the first-off X-ray inspection is too vast to contemplate. The following X-ray photos tell the story:
The picture on the left reflects a reliable component. The picture in the middle indicates a defective component – it is completely empty as it has no die. The picture on the right also shows a defective component which at least has a die but only 3 bonding wires. These defects would not have been detected without an X-ray inspection.
Most manufacturing companies are of the opinion that the initial capital outlay and cost of ownership for an X-ray facility is not justifiable. However, if one could quantify the savings that such an X-ray facility could potentially bring to the table, manufacturers would not think twice before motivating for such an instrument on their next budget cycle. The above example shows the value X-ray inspection adds.
X-ray inspection is a vital step in the test regime of the PCB and semiconductor industries. Fault finding on current package designs is extremely demanding so X-ray systems must provide, as a minimum, high resolution, high magnification and high contrast X-ray images, at the largest and different angular views. Parsec’s XiDAT digital X-ray technology equipment is providing us with that capability and with a new way of doing process control. It has added an incredible increase in confidence and quality assurance to our manufacturing process.