MEDICAL ELECTRONICS SUPPLEMENT
NON-DESTRUCTIVE 3D CHARACTERISATION OF INTERFACIAL VOIDING VIA X-PLANE
Evstatin Krastev, PhD, director of applications, Nordson Dagepresents the cutting edge in X-ray inspection technology with the latatest non-destructive 3D characterisation of interfacial voiding via X-plane
T
he need to inspect electronic components and assemblies non-
destructively is the main driver behind the development and advancement of X ray inspection technology for the electronics industry. In many cases, X- Ray inspection (2D and 3D) provides the only non-destructive techniques to inspect optically hidden components and solder joints such as BGA, POP, QFN, flip chips, through holes, TSVs, micro-bumps, copper pillars, etc. All X ray inspection systems (2D and 3D) rely on absorption contrast imaging, where the contrast is generated by the stopping power of the sample. As such, higher density and/or thicker regions of a sample produce darker regions in a grey-scale image. X ray inspection systems use this method to image features such as wire bonds and ball grid arrays down to a feature recognition size of 100nm (0.1µm). X-Plane is a novel 3D partial angle CT (PCT) technique also known as large board non-cutting CT. X-Plane provides us with the powerful capability to quickly build a 3D CT model at any location of a large printed circuit board (PCB) in a completely non- destructive way. X-plane produces high quality CT models in minutes. It is extremely easy to setup, as it uses advanced algorithms that eliminate the need of a rotation table. All other PCT techniques, that use a rotation table, are known to require difficult and lengthy set up and time consuming adjustments due to the fact that the area of interest needs to be in the middle of the rotation table. The details of the X-Plane technique are described in detail in figures (1, 2 and 3). In this article we would like to
summarise our findings of using X-plane as an effective non-destructive tool for characterising interfacial voiding in BGA devices. The figures suggests (see 1 to 3) that the interfacial voiding could be crucial for the joint strength/quality of BGA and QFN devices. 2DX is capable of providing very accurate representation only of the total voiding within the BGA joint that includes both volume and interfacial voiding (see Figure 1).
joint strength up to 10% for a very moderate amount of interfacial voiding (6% to 10%). We expect higher levels of interfacial voiding to produce much stronger negative effect. Further work is planned to expand the testing in order to gain better statistical significance and understanding of the underlying phenomena.
Figure 1: Typical 2DX voiding calculation of a BGA device as per IPC-A-610 stand
In order to characterise the interfacial
voiding we utilised the X-plane technique by performing a virtual non-destructive e-sections at the BGA joint interface as shown in Figure 2.
Figure 2:
X-plane 3D virtual e-section of the interfacial region of a BGA device with voiding calculation. Using X-plane we are able to precisely characterise the voiding at the critical interfacial region
Previous studies have shown that there is a very poor correlation between total voiding calculated as per IPC-610 and the actual interfacial voiding (See figure 3).
IN SUMMARY It is evident that interfacial voiding has a crucial negative effect on the quality and reliability of PCB devices with optically hidden joints. PCT in general is the only non-destructive technique to study interfacial voiding in BGA and QFN devices mounted on large PCBs. X-Plane has proved to be an extremely powerful and easy to use PCT technique that is not limited by the disadvantages of a rotating table. Recently, Nordsan Dage introduced the new Quadra range advanced X-Ray inspection systems featuring improved maintenance-free sealed-transmission X-ray sources with feature recognition of 100nm (0.1um) and up to 20 watts of target power. Due to the extremely advanced target
design, that does not require beam defocusing, these new X-ray sources deliver unmatched sharpness up to the full 20 Watts of target power available. The new Aspire flat panel (FP) detectors provide unsurpassed sensitivity and a pixel size of 50um for a total of 6.7 Megapixels. All these exciting developments are the base underlying the enhanced X-plane capabilities available on the new Quadra range. Armed with these new enhanced tools the company plans further X-plane studies in order to boost the industry understanding of the impact of interfacial voiding on BGA and QFN devices.
Nordson Dage
The findings of study 1 were reinforced by study 2 that used a mechanical Nordson Dage bond tester to quantify the BGA joint strength for different voiding levels. It was found that interfacial voiding negatively impacts
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Figure 3:
Total voiding vs. interfacial voiding of a BGA device. Very week correlation between interfacial voiding and total voiding (IPC-610) is evident- (R2 =0.12)
ELECTRONICS | FEBRUARY 2018 S7
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