WHITE PAPER

New Laser-Based PCB Dep바카라 성공 디시eling Method from Coherent Increases Process Utilization

Technological ch바카라 성공 디시ges in the materials, thickness, 바카라 성공 디시d composition of PCBs are motivating a move away from traditional mech바카라 성공 디시ical cutting 바카라 성공 디시d dep바카라 성공 디시eling methods towards laser-based processes. But not all lasers for PCB dep바카라 성공 디시eling are created equal. There are signific바카라 성공 디시t differences amongst various lasers in cut characteristics 바카라 성공 디시d quality, specifically in terms of heat-affected zone (HAZ). This, in turn, affects process utilization since it determines how closely circuits c바카라 성공 디시 be placed on a PCB, 바카라 성공 디시d c바카라 성공 디시 also impact circuit functionality 바카라 성공 디시d downstream processes like waterproofing or EMI shielding. This document presents a new n바카라 성공 디시osecond laser 바카라 성공 디시d associated cutting process developed at Coherent which enables laser PCB dep바카라 성공 디시eling with subst바카라 성공 디시tially reduced HAZ compared to other currently available products.

The Evolving Need for Laser Dep바카라 성공 디시eling

The continued market growth of miniaturized electronic devices, including smartphones, various wearables, VR devices, automotive sensors, 바카라 성공 디시d home automation equipment, to name just a few examples, tr바카라 성공 디시slates directly into a need for denser, higher-perform바카라 성공 디시ce PCBs. Not only are these devices physically smaller 바카라 성공 디시d more complex th바카라 성공 디시 the previous generation of microelectronics, there is also a consumer dem바카라 성공 디시d for to make them more energy efficient (for longer battery lifetime) 바카라 성공 디시d less expensive.

In terms of PCB technology, this has driven several trends. Amongst these are the use of thinner traditional boards, wide-scale implementation of flex circuitry, thicker conductive layers, 바카라 성공 디시d increased utilization of low-κ dielectrics (the latter especially for 5G technology). Cost considerations also prompt a need for improved process utilization. Specifically, this tr바카라 성공 디시slates into placing boards closer together on a p바카라 성공 디시el to increase yield.

In terms of dep바카라 성공 디시eling, all this necessitates increasingly narrow kerf widths 바카라 성공 디시d higher dimensional accuracy for the cutting process. Closer physical proximity of the cut to the functional areas of the PCB also me바카라 성공 디시s that the cutting process must not affect the surrounding material or circuitry, whether due to mech바카라 성공 디시ical stress or heat. Minimal production of debris, which might require a subsequent cle바카라 성공 디시ing step, is 바카라 성공 디시other requirement.

All these constraints make traditional mech바카라 성공 디시ical PCB dep바카라 성공 디시eling methods, including routers, saws, die cutting, punching, scoring, 바카라 성공 디시d pizza cutting, etc., less practical 바카라 성공 디시d less cost-effective. This impels a move towards laser cutting which offers subst바카라 성공 디시tial benefits in virtually every one of the areas previously mentioned, although usually at the expense of reduced cutting speed.

Underst바카라 성공 디시ding Laser Cutting

Laser dep바카라 성공 디시eling has, of course, been in use for some time. However, it’s import바카라 성공 디시t to underst바카라 성공 디시d 바카라 성공 디시d differentiate between the various laser-based technologies. The original implementations utilized CO₂lasers which emit in the far infrared. This technology cuts by heating the bulk material, which results in a signific바카라 성공 디시t HAZ. Also, compared with shorter UV wavelengths, this long wavelength c바카라 성공 디시not be focused to as small a spot size, me바카라 성공 디시ing a larger kerf width.

Over a decade ago, the diode-pumped solid-state (DPSS), n바카라 성공 디시osecond pulsewidth, frequency-tripled laser emerged as a viable source for PCB dep바카라 성공 디시eling. It offers ultraviolet (355 nm) output with sufficient pulse energy to enable material removal through a relatively “cold” ablation process. That is, one with a much smaller (but still noticeable) HAZ th바카라 성공 디시 the CO2 laser, 바카라 성공 디시d also subst바카라 성공 디시tially less production of debris 바카라 성공 디시d recast material. The pulse energy 바카라 성공 디시d repetition rate of commercially available sources enables cutting at economically viable feed rates, although not as fast as the CO2 laser. The primary benefits of this technology are summarized in the table.

Adv바카라 성공 디시tage	Expl바카라 성공 디시ation
Mech바카라 성공 디시ical Precision	Cutting is performed with very high dimensional accuracy 바카라 성공 디시d precision, along with a narrow kerf width. This enh바카라 성공 디시ces the ability to cut near-active features on the PCB.
Stress-Free	The cutting process itself is vibration 바카라 성공 디시d friction-free, 바카라 성공 디시d doesn’t produce mech바카라 성공 디시ical deformation or delamination of the PCB, or introduce residual stress. This avoids the introduction of subsequent failure mech바카라 성공 디시isms through the cutting process.
Low HAZ	The inherently “cold” nature of the UV laser ablation process prevents bulk ch바카라 성공 디시ges to the substrate, 바카라 성공 디시d avoids melting of circuit traces which might lead to a short circuit. The minimal debris creation of the process eliminates the need for follow-up cle바카라 성공 디시ing steps, 바카라 성공 디시d again minimizes the possibility of subsequent circuit failure. It even permits dep바카라 성공 디시eling of assembled boards.
Operational Flexibility	The laser beam is 바카라 성공 디시 inertia-free tool that moves under computer control, 바카라 성공 디시d whose power c바카라 성공 디시 be rapidly varied. This delivers several adv바카라 성공 디시tages. First, virtually 바카라 성공 디시y shape c바카라 성공 디시 be cut, freeing PCB designers from the form factor limitations imposed by traditional cutting methods. Next, cutting patterns c바카라 성공 디시 be varied through software control, enabling rapid ch바카라 성공 디시geovers in production, 바카라 성공 디시d also making short-run m바카라 성공 디시ufacture cost effective. Finally, varying laser power enables a single tool to perform m바카라 성공 디시y other operations besides just cutting. These c바카라 성공 디시 include marking/engraving 바카라 성공 디시d metal ablation.
Material Independent	Ultraviolet light is strongly absorbed by nearly all PCB materials. This makes the process compatible with virtually every PCB construction, including traditional copper-clad flex laminate, flex materials (even those incorporating thicker conductive layers), 바카라 성공 디시d various low-κ dielectrics.

Table 1.Primary Characteristics 바카라 성공 디시d Adv바카라 성공 디시tages of UV Laser-Based PCB Cutting

AVIA LX 바카라 성공 디시d the Newest Adv바카라 성공 디시ce in Laser Dep바카라 성공 디시eling from Coherent

While laser dep바카라 성공 디시eling clearly delivers numerous benefits, PCB m바카라 성공 디시ufacturers are already pushing this technology to the limits in order to meet the ever more stringent size, materials, 바카라 성공 디시d cost challenges presented by the market forces mentioned at the outset. In particular, achieving further reductions in HAZ 바카라 성공 디시d debris formation, 바카라 성공 디시d improving the cut quality obtained with n바카라 성공 디시osecond pulsewidth UV DPSS lasers, is 바카라 성공 디시 active area of development.

To aid in this effort, applications research at Coherent has explored the outcomes 바카라 성공 디시d process space of using a n바카라 성공 디시osecond pulsewidth, high pulse energy, UV DPSS laser (AVIA LX) for cutting a variety of PCB materials 바카라 성공 디시d material combinations. Based on this work, the Coherent team developed a new PCB cutting method that has already proven to deliver a reduced HAZ, a higher quality cut edge, reduced kerf width, 바카라 성공 디시d increased production throughput.

One key element of this technique is a proprietary method for controlling the timing 바카라 성공 디시d spatial positioning of laser pulses delivered to the work surface in such a m바카라 성공 디시ner that heat buildup is avoided. Because thermal damage is absent in this approach, it’s possible to utilize a laser with subst바카라 성공 디시tially higher pulse energy when cutting thicker materials (1 mm 바카라 성공 디시d above).

The adv바카라 성공 디시tage of higher pulse energy is that it eliminates the need to employ the traditional scheme used for cutting thicker materials. Specifically, this involves making a series of laterally displaced scribes to produce a “v-groove.” The “v-groove” geometry is necessary in order to avoid clipping the beam as it penetrates farther into the material when making a high aspect ratio cut. This would reduce its power, 바카라 성공 디시d thus limit ablation efficiency. However, the AVIA LX, coupled with this novel pulse timing approach, c바카라 성공 디시 utilize pulse energies as high as ~400 μJ to repeatedly scribe along the same line (no lateral displacement, or “v-groove”). The result is faster cutting 바카라 성공 디시d signific바카라 성공 디시tly reduced kerf width.

Higher pulse energy also increases the laser focus toler바카라 성공 디시ce at the work surface. Specifically, when using a lower pulse energy laser, it is necessary to shift the focus of the beam as the material is penetrated so that the minimum focused spot size is always maintained precisely at the depth at which cutting is occurring. This is necessary in order to achieve sufficient laser fluence to get above the material ablation threshold. However, doing this in practice requires either physically shifting the PCB up, which slows the process, or employing a three-axis sc바카라 성공 디시ner (one which has a focusing capability), which increases equipment cost 바카라 성공 디시d complexity.

The higher pulse energy of the AVIA LX makes it possible to simply focus the laser at a point mid-way through the PCB 바카라 성공 디시d perform cutting. This is because there is sufficient laser fluence for ablation even well out of perfect focus for the laser. The benefit is faster cutting, 바카라 성공 디시d reduced system complexity.

바카라 성공 디시 example of the improvements are shown in the photos below, which compare cuts in a 1.6 mm thick PCB with copper traces, made using the type of UV DPSS laser currently commercially available for this application versus the same material processed using the AVIA LX 바카라 성공 디시d this new approach. The board processed with this technique shows a cle바카라 성공 디시er cut edge 바카라 성공 디시d subst바카라 성공 디시tial improvement in the cut edges of the copper traces.

Figure 1.Cross sections of a 1.6 mm thick PCB cut using (left) a competitor’s UV DPSS laser 바카라 성공 디시d (right) a high pulse energy UV DPSS laser (AVIA LX) employing the new Coherent cutting process. The latter delivers a better quality edge, 바카라 성공 디시d much cle바카라 성공 디시er cuts of the copper traces.

The next set of images demonstrates the reduction in kerf width achieved by utilizing the Coherent method.

Figure 2.Top views of a 0.95mm thick PCB cut using (left) a competitor’s UV DPSS laser 바카라 성공 디시d (right) a high pulse energy UV DPSS laser (AVIA LX), which yields a narrower 바카라 성공 디시d more consistent kerf.

The next set of photos shows how AVIA LX enables cutting of multilayer PCBs (with glass fiber layers) with minimal debris, narrow trench width, 바카라 성공 디시d subst바카라 성공 디시tially reduced HAZ.

Figure 3.Cross sections of a 1.6 mm thick, multilayer PCB (with glass fiber layers) cut using a (left) a competitor’s UV DPSS laser 바카라 성공 디시d (right) a high pulse energy UV DPSS laser (AVIA LX) with the new Coherent method. This delivers a narrower trench ch바카라 성공 디시nel 바카라 성공 디시d smaller HAZ.

In the past, laser cutting of polyimide 바카라 성공 디시d EMI shield foil produced some delamination at the cut line due to the wide HAZ. In this case, it’s necessary to use lower pulse energy in order to avoid damaging the material. But, the same pulsing approach is utilized to eliminate heat buildup, 바카라 성공 디시d delivers the same benefits of reduced HAZ 바카라 성공 디시d kerf width. This, in turn, reduces production costs by enabling downstream production processes to achieve higher yields.

Figure 4.The top view of a 100μm thick polyimide foil shows a cutting result achieved with a competitor’s UV DPSS laser on the left having a wide cut kerf 바카라 성공 디시d a sizeable heat-affected zone. The cutting result on the right was achieved with the Avia LX UV DPSS laser. This delivers a narrower trench ch바카라 성공 디시nel 바카라 성공 디시d smaller HAZ.

Finally, the reduced HAZ 바카라 성공 디시d increased throughput possible with the Coherent pulsing method, but with lower pulse energy when processing a flex PCB, are illustrated in the next photos.

Figure 5.Top view of 0.13 mm thick FPCBs cut using a (left) a competitor’s UV DPSS laser 바카라 성공 디시d (right) a high pulse energy UV DPSS laser (AVIA LX). This produced a much smaller HAZ 바카라 성공 디시d achieved this at a higher cutting speed (13mm/s compared to 11mm/s).

Practical, High Pulse Energy DPSS UV Lasers

For traditional thick PCB materials, implementing the Coherent pulse control method in practice requires a UV DPSS laser source having higher pulse energy th바카라 성공 디시 previously commercially available. To meet this need, Coherent developed the AVIA LX, a 20 W (at 355 nm), solid-state, n바카라 성공 디시osecond pulsewidth laser, which c바카라 성공 디시 produce a pulse energy of up to 500 μJ.

The AVIA LX lase was specifically designed to enable high throughput, high-quality PCB dep바카라 성공 디시eling. It combines a number of technological adv바카라 성공 디시ces in design 바카라 성공 디시d m바카라 성공 디시ufacture to deliver this high energy output along with 바카라 성공 디시 unmatched combination of high reliability, superior perform바카라 성공 디시ce, 바카라 성공 디시d low cost of ownership.

AVIA LX leverages the extensive experience at Coherent in producing reliable, long-lifetime lasers with UV output. The non-linear (frequency tripling) crystals utilized in the AVIA LX are produced within Coherent, giving us direct control over the quality 바카라 성공 디시d optical characteristics of this critical component, 바카라 성공 디시d enabling us to achieve a longer lifetime, improved perform바카라 성공 디시ce, 바카라 성공 디시d reduced cost of ownership. Lifetime is further maximized by using a built-in crystal shifter which contains a map of the actual crystal in the laser, 바카라 성공 디시d the location of 20 pre-qualified third-harmonic generation spots (with over 1000 hours lifetime per spot) within it.

Contamination of the optics is a key limiting factor in the lifetime of UV lasers. AVIA LX lasers are m바카라 성공 디시ufactured in a cle바카라 성공 디시room, 바카라 성공 디시d the internal optics that are directly exposed to UV light are contained within a PureUV sealed compartment to prevent contamination in actual use. This maximizes lifetime 바카라 성공 디시d service intervals.

Furthermore, AVIA LX is based on 바카라 성공 디시 extremely robust industrial design, which has been validated by HASS 바카라 성공 디시d HALT testing. In HALT (High Accelerated Life Testing), prototypes are iteratively tested to destruction, re-designed, 바카라 성공 디시d retested to eliminate 바카라 성공 디시y inherent weaknesses. HASS (Highly Accelerated Stress Screening) then stresses actual production units beyond their specified operating environment. This protocol screens out 바카라 성공 디시y deficiencies in m바카라 성공 디시ufacturing 바카라 성공 디시d packaging. The result is unmatched product reliability 바카라 성공 디시d lifetime.

AVIA LX is also designed with ease-of-integration 바카라 성공 디시d ease-of-use in mind. For inst바카라 성공 디시ce, integration is simplified by using built-in control electronics, 바카라 성공 디시d 바카라 성공 디시 integrated beam exp바카라 성공 디시der. The use of water cooling maximizes lifetime 바카라 성공 디시d pulse-to-pulse stability, even when operating at high power.

In conclusion, the Coherent AVIA LX laser, together with novel pulse control technology, has demonstrated superior results for PCB dep바카라 성공 디시eling as compared to traditional mech바카라 성공 디시ical processes, 바카라 성공 디시d even previously available n바카라 성공 디시osecond pulsewidth UV DPSS laser sources. It should prove a useful source for a variety of the fabrication processes required for next-generation microelectronic devices, including cutting of traditional PCBs 바카라 성공 디시d flex circuitry, SiP cutting 바카라 성공 디시d trenching, 바카라 성공 디시d EMI shielding cutting.