electronics The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices. Electronics uses active devices to control electron flow by amplification ...

, a cross section, cross-section, or microsection, is a prepared electronics sample that allows analysis at a plane that cuts through the sample. It is a destructive technique requiring that a portion of the sample be cut or ground away to expose the internal plane for analysis. They are commonly prepared for research, manufacturing

quality assurance Quality assurance (QA) is the term used in both manufacturing and service industries to describe the systematic efforts taken to ensure that the product(s) delivered to customer(s) meet with the contractual and other agreed upon performance, design ...

, supplier conformity, and failure analysis. Printed wiring boards (PWBs) and electronic components and their solder joints are common cross sectioned samples. The features of interest to be analyzed in cross section can be nanometer-scale metal and dielectric layers in

semiconductors A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...

up to macroscopic features such as the amount of solder that has filled into a large, 0.125in (3.18mm) diameter plated through hole.

Preparation

Cross sections can be prepared by several methods typically chosen based on the scale of the feature of interest because the technique affects the smoothness of the final polish. Smoother polishes allow an analysis of smaller features but can also take longer or be more expensive to prepare. Cross sectioning hard materials such as alumina might require a different technique than a soft material like

gold Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile met ...

or soft plastic.

Mechanical grinding and polishing

Mechanical grinding and polishing is a common method of preparation to analyze features on the order of 1s to 10s of microns to macroscopic features. Samples may first be cut down in size, for example, around a

via Via or VIA may refer to the following: Science and technology * MOS Technology 6522, Versatile Interface Adapter * ''Via'' (moth), a genus of moths in the family Noctuidae * Via (electronics), a through-connection * VIA Technologies, a Taiwan ...

in a PWB or around a

ceramic capacitor A ceramic capacitor is a fixed-value capacitor where the ceramic material acts as the dielectric. It is constructed of two or more alternating layers of ceramic and a metal layer acting as the electrodes. The composition of the ceramic material de ...

soldered to a PWB. Samples may be prepared by encapsulation in a rigid material such as

epoxy Epoxy is the family of basic components or cured end products of epoxy resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide functional group is also coll ...

to keep the sample intact during grinding and with a vacuum step to fill in air gaps and create a solid sample with no voids. However, cross sections of some samples can be prepared with no encapsulation. Encapsulated samples are prepared using a rough grinding medium to remove material from the sample until just before the plane of interest is reached. Equipment can help automate the process by holding grinding and polishing media firm and then spinning it so a sample can be pressed against it. Typical grinding media are

silicon carbide Silicon carbide (SiC), also known as carborundum (), is a hard chemical compound containing silicon and carbon. A semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder and crystal sin ...

and

diamond Diamond is a Allotropes of carbon, solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Another solid form of carbon known as graphite is the Chemical stability, chemically stable form of car ...

, which can be in the form of disposable discs impregnated with the grinding media or a slurry applied to a reusable pad. Successively finer media are used to finish grinding to the plane of interest and to polish at the plane of interest. Each successively smaller grit is used to remove the scratches and damage caused by the previous grit.

Mechanical cutting or milling

Some equipment allows for preparation of cross sections by direct cutting or milling.

Other techniques

Focused ion beam Focused ion beam, also known as FIB, is a technique used particularly in the semiconductor industry, materials science and increasingly in the biological field for site-specific analysis, deposition, and ablation of materials. A FIB setup is a s ...

, ion beam milling, and cleaving are common techniques in the semiconductor fabrication industry.

Printed wiring boards

Manufacturers of substrates used in electronics prepare cross sections of a final product for quality assurance. In cross section, the quality of drill holes can be assessed and the plating quality and thickness in vias can be measured. Voids in the substrate materials may be seen which show the quality of the lamination process.

Electronic components

Viewing the internal structures of electronic components by cross section can reveal problems with manufacturing and material quality. In integrated circuits, a cross section can reveal the die, and its active layers, the die paddle, and 1st level interconnect (wire bonds or solder bumps).

Solder joints

Cross sections of component solder joints are commonly prepared to assess the quality and extent of the metallurgical bond. This analysis can be used to help determine any issues during the soldering processes that could lead to

solder fatigue Solder fatigue is the mechanical degradation of solder due to deformation under cyclic loading. This can often occur at stress levels below the yield stress of solder as a result of repeated temperature fluctuations, mechanical vibrations, or mec ...

and failure. Solder joint cross sections are also commonly prepared during failure analysis to see cracks in the solder. Crack morphology can lead to identification of the type of stress and ultimately the root cause of the solder joint failure.https://nepp.nasa.gov/docuploads/D084F3EB-BFA9-4733-8F535584A99095F9/Dernning_BGAInspection.pdf

Analysis techniques for cross sections

Analysis of polished cross sections can be performed with a variety of techniques. Images are commonly taken with

optical microscopy Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviole ...

and scanning electron microscopy. Chemical analysis can be done with energy dispersive x-ray spectroscopy (EDS). Hardness testing can also be performed.

References

{{Reflist, 30em Semiconductor device fabrication Quality control