There can be differences in the height the solder rises up the ball due to the paste volume and the wettability of the terminations. This is because the ball does not reflow but the paste does. With high-temperature balls like 90%lead/10%tin there will be a demarcation line between the solder alloy and the ball. With balls that become liquid with the paste, there is little evidence of any demarcation between the two solder surfaces. Solder joints to high temperature terminations do look different! – see Figure 2.Įxamples of the soldering quality on high-temperature balls often featured on ceramic ball grid arrays (CBGA) should be included due to the difference in surface appearance. Criteria should include conventional BGA, chip scale package (CSP), package on package (POP) and flip chip terminations with tin/lead or lead-free eutectic and high-temperature ball terminations. This is true for both X-ray and optical inspection, as assessing joints can be daunting for staff members new to these techniques. Ideally some visual standards should be provided for operator reference during final inspection or during process monitoring. Example of high-temperature ceramic package satisfactorily soldered to the pad surface. If the budget is available, the ideal situation is to have both methods of controlling and defining the manufacturing process, or to have samples from production examined by an external source.įigure 2. However, this is not feasible to use on inner ball terminations or where the overhang obscures the terminations when tilting the board assembly.īoth X-ray and these specialist inspection systems have limitations on the process issues and defects they can detect. It is possible to examine the outer row of ball terminations with traditional inspection equipment, depending on stand-off height and the overhang on the side of the BGA. The author has conducted many hands-on training courses on inspection criteria for both optical and X-ray inspection, and produced the first training videos and interactive CD-ROM on area array inspection X-ray was of course the first choice for BGA inspection when area array devices were first introduced, and is commonly used in industry.
ALTIUM DESIGNER ALTERNATIVE FREE
With care, design engineers can always leave areas free of parts, particularly on the corners of adjacent sides of a device.Īlthough not covered in this article, X-ray criteria are available, and this is the popular alternative to optical inspection. The close proximity of components to the body of the device to be examined may also limit the opportunity for inspection, particularly when scanning along the sides of devices. Often there are limited stand-off heights and overhang restrictions due to the body of the package. This type of defect is intermittent so finding it in the first place is a challenge. One of the biggest challenges to inspection and process improvement has been head-in-pillow defects.
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