A few months ago, a customer came into our Monrovia lab intent on processing application samples using hot bar reflow soldering - the part was specifically developed with that technology in mind. Sr. Lab Technician Vickie Buckley, however, took one look at the part and decided that reflow soldering wasn't the optimum process: the wires were too small and would flatten out before the solder melted and reflowed creating a proper bond on the terminals below. All was not lost, however, her 20+ years of experience told her that the application could be done using thermocompression bonding; they moved over to that equipment and had immediate success! The customer went home content that he had a process that would work!
Scenarios like this play out in our labs every day. Thankfully, we have both the expertise and the broad range of equipment to address applications with multiple technologies depending on the material, part accessibility, mechanical and aesthetic requirements, and budget. Avoid costly redesign by getting it right the first time. Here are some tips for doing just that:
- Choose materials carefully. Our FREE Weldability App can help you make selections based on whether or not they can be successfully joined.
- There really is a 'right' process - be open to finding it. Our customer may indeed have been able to find a reflow soldering solution that worked, but it wouldn't have been as fast or as robust as thermocompression bonding and while less expensive to implement, would have cost more money over time.
- Review our Fundamentals and Part Design Guidelines early in development. Better yet, contact our lab engineers - folks familiar with the different joining processes - and get their opinion regarding designing parts for manufacturability. FREE!
Are you working on a new design? Want some help? Contact us for a FREE sample evaluation today!
Flexible circuits are found everywhere: cell phones, tablets, flat screen tvs, cameras, rockets, satellites – anywhere electrical connections are required in three or more axes; where the assembly is required to flex during operation; where weight is an issue; and, as devices get smaller and smaller - where board thickness or space is a driving factor. They are most often connected using hot bar reflow soldering which utilizes a thermode heating element and allows for a more repeatable and consistent joint quality than traditional hand soldering, and are commonly made of two layers of polyimide encapsulating copper traces. Copper trace thickness generally ranges from 0.0007 – 0.004 inches, and thickness of the flex is between 0.001 – 0.0047 inches.
The three most common flex circuit termination designs for successful pulse heated reflow soldering are “exposed lead,” “single-sided,” and “open-windowed.” Choose the one that best suits your design and manufacturing needs:
- “Exposed lead”- both sides of the polyimide material are removed, leaving the traces free of insulation. This allows the thermode (hot bar) to contact the traces directly, conducting heat to the parts and creating the bond. This design tolerates some excess solder on the pads, as there are open areas for the solder to flow into. Exposed leads can be easily bent or damaged; handle carefully!
- “Single-sided” - polyimide is removed on one side only. Heat is conducted from the thermode, through the polyimide, to the exposed traces underneath. The polyimide thickness in the joint area can be no more than 0.002” to enable proper heat conduction without burning. This design is not tolerant of excess solder on the pads, as there is little room for excess to flow. This design is well suited to fine pitch applications.
- “Open windowed” – as it sounds: joint area is exposed in a ‘window’ in the polyimide. This design is a little more durable and tolerant of harsher handling. The traces are exposed, so thermal transfer is good and excess solder has space to flow into. Thermode sizing is critical, however, as it must fit into the window.
Hot bar reflow soldering of flexible circuits is a stable and well controlled process. The process window can be made substantially wider by a joint design that promotes easy and equal heat distribution, accommodates the flow of solder, and can compensate for variations in process.
Fiber lasers come in two flavors: single mode and multi mode. What are the differences and which should you choose for your fiber laser micro welding application?
Single mode fiber lasers are typically delivered via fiber with a core diameter of around 9 microns producing a narrow, high intensity beam which can be focused down to a spot size as small as 10 microns. This high intensity, small spot is ideally suited for laser cutting applications, but generally not great for welding, as weld widths are too narrow to accommodate most production fit-up tolerances.
Multi-mode fiber lasers, by contrast, utilize fibers with core diameters between 50 – 300 microns resulting in lower intensity, more uniform, “flat top” beams which promote an enlarged melt zone more in line with welding requirements.
This figure shows a schematic of the laser exiting the fiber and the cross section of power intensity through the beam diameter for the two modes:
Consider also laser alignment to the weld joint –stack-up positional tolerances and gaps between weld edges mean that aligning the beam to the joint line generally requires a spot size of at least 200 microns. To attain that large a spot with a single mode fiber laser, you’d need a focal length of 2-3 feet! Not practical in any welding system... Furthermore, the single mode's high central intensity which tapers rapidly to the edges, concentrates all of its power in a small volume of material. If there is any gap in the joint, the weld will be undercut or underfilled, and, if the intensity is too high, the laser will remove material.
The multimode fiber laser beam more equally distributes its intensity across the weld, resulting in more stable welding conditions. It is less sensitive to gaps between welding surfaces, and its larger flat top intensity profile melts more base material volume, effectively bridging gaps as needed.
The figure below shows cross sections of bead on plate welds for single mode and multimode lasers in 0.06” thick stainless steel utilizing (a) Single Mode Fiber Laser at 500W, 300ipm with a 30 micron spot size (b) Multi Mode Fiber Laser at 700W, 100ipm with a 150 micron spot size (c) Multi Mode Fiber Laser at 1kW, 80 ipm with a 250 micron spot size:
There are some cases where single mode fiber lasers can be implemented effectively in welding applications; high speed lap welding, for example, or very close fitting joints that can be welded with significantly lower laser power, but still achieve a certain penetration over multi mode lasers.
Posted by
Mark Boyle on Fri, Feb 24, 2012 @ 04:50 PM
In our last blog, we explored when laser markers make sense in comparison to other marking technologies. Key reasons included high mark and material variation, fragile material, and mark durability. But did you know laser markers can also be used for machining? Yep - your laser marker can do double duty as a micromachining system!
Although laser markers are typically used for labeling parts with serial numbers and other identification codes, they can also be used for some basic material processing, e.g., drilling holes and cutting materials. While they may not function as well as a laser designed specifically for the process, they can provide insight to the feasibility of the process. Here are some of the manufacturing processes that can be achieved with lasers:
- Drilling removes material to create a hole in a material. Laser drilling is achieved by repetitively hitting the same location until enough material has been removed for a hole. Hole diameters achieved with a laser can be as small as <50 um (depending on optics and material).
- Cutting removes material to create a slot. Laser cutting works by directing the output of a high-power laser at the material to be cut. The material melts, burns, vaporizes, or is blown away by a jet of gas, leaving an edge with a high-quality finish.
- Trimming utilizes a laser to adjust the operating parameters of an electronic circuit. By selectively removing material from the surface, a device like a resistor can be fine tuned.
- Scribing removes material just to a certain depth so it can be easily broken along the lines created.
- Ablation removes material from a solid surface by irradiating it with a laser beam. This is done without damaging the substrate below.
Micromachining with a laser marker has distinct advantages over competing technologies including the fact that it is a non-contact technology, there is no need to retool the machine for each job, it can work with fragile, brittle materials, and laser markers are great for precision part work down to the micrometer scale.
Yes, there are some limitations to laser processing. The time required to do each of these processes depend on the laser power available and the properties of the material (type, thickness, etc). In addition, the properties of the laser beam inhibit particularly deep drilling and limit the aspect ratio achievable for holes close to the beam diameter. In spite of those limitations, laser micromachining has become a major industrial tool for a wide range of industries.
Laser markers are generally low powered variants of the ideal laser micromachining system, but could be used for R&D, providing an indication of part manufacturing feasibility, or low volume production.
So keep that in mind the next time you have a micromachining application - and give your laser marker a go at the process!
Interested in a free feasibility study? We can help!
Posted by
Mark Boyle on Wed, Dec 21, 2011 @ 06:35 PM
Product identification, serialization and tracking are key elements for any production environment. Parts are labeled with all kinds of marks: alpha-numeric serial numbers, date stamps, barcodes, etc.. There are a lot of marking methods available out there including dot-peen, chemical etching, pad printing, ink-jet printing, and laser marking. As manufacturers of laser markers and laser marking systems, we, of course, believe that there are many good reasons why laser marking makes sense in your manufacturing operation?
Consider these things:
- Do you need one machine to mark both metals and plastics?
- Are your parts fragile?
- Do you need to mark graphics, logos or barcodes?
- Do you need to mark many parts, very quickly?
- Does the mark need to be permanent?
- Would you like to have one machine capable of addressing all of the above?
- Would you like a process with no consumables or maintenance?
If the answer to all or most of the above questions is 'yes' you should seriously consider laser marking.
We're not just saying that because we make lasers - consider the following: Dot-peen is a mechanical marking method, meaning that it marks are made by gouging material using a hardened stylus - it’s cheap and great for simple marks on metals but requires the part to be clamped, is a slow process and cannot mark non metals or fragile parts. Electrochemical etching produces very high quality marks but has very limited mark content flexibility and is suited only to metals. Pad printing is a marking method that transfers an image from a plate via a silicone pad to a part. It is a high volume, low mix technology; fast but not flexible. And ink jet marking, accomplished by spraying small dots of ink directly onto moving parts, is very fast and efficient, but easily worn off, and, therefore, not considered a permanent marking method. This is highly undesirable for markets like automotive, where parts are likely to undergo a significant amount of wear, or medical where ink/chemicals are frowned on. And don't forget the cleaning required in a process which uses ink/chemicals like this. Something to consider if you're trying to go a little more 'green' in your manufacturing processes.
Laser marking, by contrast, is a direct, non-contact marking method which can be used on a variety of materials. For example, fiber laser markers make excellent marks on metals, plastics, and ceramics. It's a clean marking method that doesn't require water, oils, chemicals, or post-processing cleaning. Laser markers can mark fonts, barcodes, and pictures without the need to retool. It has already been established in a wide array of markets, most notably the medical device, automotive, and electronics industries. The picture below shows a wide range of applications for laser marking:
OK, laser markers do cost more to acquire, however, they provide a quick ROI over 1-2 years with added functionality, material flexibility, speed and zero maintenance. Laser markers are continuing to come down in price with so they may not be as expensive as you think!
So, just when DOES a laser marker make sense?
- Your parts are fragile and cannot withstand the percussive nature of a marking method like dot peen
- You have high mix/high volume part marking needs
- You’re working in a high-tech industry (aerospace, automotive, medical, etc.) where permanent, readable marks are imperative
- You’d like your manufacturing process to be a little more ‘green’
Wire and sinker EDM are two of the oldest, most widely used traditional precision cutting technologies, but more and more manufacturers and jobshops are replacing or complementing their wire EDM capabilities with laser cutting systems which generally feature a smaller footprint, faster processing times, and lower cost-per-part ratio. Here are 3 reasons for YOU to consider laser cutting:
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Faster Processing Times and Higher Quality Cuts - Wire EDM works in a two dimensional geometry, so parts with more geometry features - even simple bevels - require separate set up, programming and cutting processes, all of which add significantly to the total process time. Laser cutting systems can process multiple featured parts using up to 5 axes of motion in a single step. And single pass laser cut quality is superior to wire EDM cut quality; wire EDM may require up to four (4) separate passes (more time!) to achieve the same quality. Also, with a focused spot size of 0.001” lasers offer increased cut resolution for internal radii.
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Lower Cost per Manufactured Part - with linear motors and direct drive rotary stages laser cutting speeds are extremely fast and precise. For tube cutting with single sided features, laser cutting is significantly faster than wire or sinker EDM providing substantial cost savings per part. As laser cutting is a “tooless” process there is no requirement for equipment maintenance as needed for wire EDM machines.
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Small Footprint - Is floor space a premium? The typical wire EDM system measures up to 10 or 12 feet square. Laser cutting systems are half that size - maybe 5 to 6 feet square.
If you're looking to maximize productivity, now might be the time to consider adding a laser cutting system. Get our whitepaper for a complete overview of laser cutting and how it compares to traditional cutting technologies.
