electronics Electronics is a scientific and engineering discipline that studies and applies the principles of physics to design, create, and operate devices that manipulate electrons and other Electric charge, electrically charged particles. It is a subfield ...

, 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 assure 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

semiconductor A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities (" doping") to its crystal structure. When two regions with different doping level ...

s 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 Aluminium oxide (or aluminium(III) oxide) is a chemical compound of aluminium and oxygen with the chemical formula . It is the most commonly occurring of several aluminium oxides, and specifically identified as aluminium oxide. It is commonly ...

might require a different technique than a soft material like

gold Gold is a chemical element; it has chemical symbol Au (from Latin ) and atomic number 79. In its pure form, it is a brightness, bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal ...

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 in a PWB or around a ceramic capacitor 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 Curing (chemistry), cured end products of epoxy Resin, resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide fun ...

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 wide bandgap semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder a ...

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. Diamond is tasteless, odourless, strong, brittle solid, colourless in pure form, a poor conductor of e ...

, which can be in the form of disposable discs impregnated with the grinding medium 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, 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, 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 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, ultravio ...

and

scanning electron microscopy A scanning electron microscope (SEM) is a type of electron microscope that produces images of a sample by scanning the surface with a focused beam of electrons. The electrons interact with atoms in the sample, producing various signals that ...

. Chemical analysis can be done with energy-dispersive X-ray spectroscopy (EDS). Hardness testing can also be performed.

References

{{Reflist, 30em Quality control Semiconductor device fabrication