September, 2019
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Fast and Reliable: X-Ray Inspection Detects and Measures Voids
W
hile the technology of inline X-ray (AXI) and automatic optical inspection (AOI) dif- fer, both systems are designed to provide
high-speed and high-quality 3D images. One exam- ple of an important use of X-ray is reliable void detection, such as in the manufacturing of elec- tronic assemblies with BGAs and LEDs. There are a variety of factors responsible for
the formation of voids, and X-ray is the only non- destructive method available for accurately detect- ing them in solder joints. One factor is the behav- ior of solder pastes with different compositions, and another is the surface finish of the PCB and components to which they are soldered during the production process. Pollutants that remain on the PCB after
cleaning are also a cause of voids. Also, the quality of solder paste can degrade when stored too long, which may contribute to increased voiding. The joint quality is also impacted by the specific reflow oven parameters selected during production. If there is insufficient time for flux in the solder joint to escape during reflow, voids may form. The standards set by IPC serve
as guidelines for process optimization: IPC J-STD-001 and IPC-A-610 specify the requirements for soldered electri- cal and electronic assemblies and the acceptance criteria for electronic assemblies, respectively. Helpful in - for mation specific to voids and void measurement for BGAs can be found in IPC-7095D.
Voiding Thresholds Viscom’s inspection software for
BGA solder joints uses a default threshold setting that doesn’t permit the total area of all voids to exceed 25 percent of the solder area. “This default threshold is based
on years of experience at Viscom, but can naturally also be adjusted to meet any specific inspection needs of production,” explains Axel Klapproth, head of application, serial products, Viscom AG. Inline 3D X-ray can obtain horizontal and vertical slice images of objects under inspection. This opens up new and interesting possibilities in void measurement, such as measuring the void-substrate and void-component distances. In the case of BGAs, IPC-7095D
states that the positions of cavities in solder joints are critically more important than their size or quantity. Consequently, small gaps between the edge of the solder joint and the contact surface can significantly impact the point of breakage once a crack begins to form. During process qualification,
void measurement results can be used to test and statistically differen- tiate between solder pastes, reflow settings and even different surfaces, until defined limits are actually met. Viscom’s advanced software meas- ures individual voids, calculates the total void percentage and evaluates the results.
3D AXI for LEDs Meeting specified thresholds
during ongoing production requires that inspections be performed reli- ably and precisely. The goal is to ensure high-quality solder joints in each product. The impact that voids can have on product quality is a well- known issue in the manufacturing of LEDs as well. From interior lighting to street
By Olaf Szarlan, Marketing, Viscom AG
lamps and displays, there are countless ways to use LEDs. For industrial designers, this brings with it an abundance of creative possibilities for making lighting designs a reality. The automotive industry was quick to recognize the potential of this technol- ogy, which has long been established as standard in vehicle lights, such as turn signals and headlights. Advantages of LEDs include long service lives, high light yields and low energy consumption.
Crucial Heat Dissipation LEDs emit heat as well as light. Quick dissi-
An X-ray image (left) can be used to perform precise void measurements (right).
pation of heat is critical for their longevity. The standards in IPC-A-610 Revision G, regarding components with connections to heat sinks on
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