Marking and Engraving

Lasers have long been used to mark metal products by precision engraving – removing a small amount of surface material. Another laser technique is laser annealing where the local heating causes a color change in the surface. More recently, black marking based on ultrashort pulse (USP) lasers is used to create high-contrast marks on stainless steels and aluminum with no negative impact on surface protection. This technique is increasingly used for medical reusables, personal electronic packages, and consumer appliances (white goods).

The overarching trend for miniaturization in semiconductors requires marking at higher spatial resolution with excellent depth control. The need to apply these marks to front and rear surfaces of wafers is met by the use of shorter (e.g., ultraviolet) laser wavelengths often with shorter pulse widths. Coherent software supports all common fonts used in wafer marking. Molded packages are usually marked with infrared or green lasers. The uses of a f-theta scan lens with a wide field of view enables optimized machines to mark full trays and ICs on lead frame without the need for indexing.

There are several ways to mark colored, transparent or opaque plastics using lasers, including bleaching, color changes, carbonization, engraving (ablating), foaming, or a combination of these. Plastic marking is commonly performed using either solid state or fiber lasers. Ultraviolet wavelengths are increasingly preferred in industries such as semiconductors where high mark resolution and eliminating peripheral thermal effects are primary concerns. Typically, an excimer laser is used for marking transparent materials.

There are numerous specialty laser marking techniques like tactile marking of plastics which produces a raised mark by deliberately creating a type of recast material on the surface or surface removal where a top layer of a lacquer or paint is removed to reveal a substrate of a different color or reflectivity underneath. Wood and other organics are sometimes marked by combining engraving and slight carbonization to increase visibility. Coherent also supports applications where marking is intimately combined with another process such as label marking and kiss cutting.

Coherent lasers are the ideal source for microstructuring glass.

When marking and engraving glass, either a 193 nm excimer laser such as the ExciStar is directly absorbed by the glass or a high intensity laser irradiance enables a multi-photon process and non-linear absorption effects in transparent material such as flat panel display glass. The 193 nm ExciStar is used for surface-near engraving whereas the high peak power of the Matrix DPSS laser, easily engraves inside the glass.