Low-Temperature Soldering FAQ

Have a question about low-temp soldering? Check these answers.

Utilizing PulseForge photonic soldering technology, we are able to solder LEDs, resistors and capacitors onto conductive ink traces in a matter of milliseconds.

We can categorize conventional processes into volumetric and selective: with conventional thermal processes, like reflow ovens, all parts inside the soldering chamber get to the same temperature, constituting a volumetric process; laser soldering, which heats up only the solder joints, is a selective process.

Most manufacturers are familiar with reflow ovens, and regularly experience processing with slow heating and cooling cycles. And because all parts get to the same temperature, the thermal stability of substrates, components, conductive tracks, coatings, etc., have to be very high. To get around this limitation, selective heating with lasers is often used. However, laser processing is too selective, soldering only a single joint at a time. And while each single joint can be soldered in seconds, in highly dense panels, there could be thousands of individual joints that need to be soldered – a speed bottle-neck in high-volume production.

PulseForge Soldering’s high-intensity flashlamp technology does not damage heat-sensitive components and substrates, like reflow ovens, and, unlike lasers, PulseForge Soldering uses a broad-spectrum, wide-area light source, with the capability of processing entire panels and boards in seconds.

With its broad-spectrum, wide-area light source, PulseForge soldering has selectivity similar to lasers, while also having the capability of processing whole panels and boards within seconds. A note on spatial selectivity. If you have a board with a black soldermask, that’s something to be considered, because it is going to be the primary heat absorber. Customer feedback has been very positive and accommodating: understanding the PulseForge technology, if they have a dark-colored soldermask, they simply change to a less-absorbent color.

Because energy consumption happens only when the flashlamp is on (millisecond timescales), PulseForge Soldering is much more energy efficient than conventional thermal processes. An added plus, quick ramp-up and cool down with PulseForge technology translates to a carbon footprint significantly less than conventional thermal reflow ovens.

We know that you cannot put PT or fabrics, for example, in an oven, and expect them to survive. With our years of experience in controlling pulsed power, and tapping into peak powers and average energy densities, we invented extremely high-powered xenon gas filled lamps that emit white light. Inks, solders, tracks, anything that is dark in color absorbs this light and gets hot, while heat-sensitive substrates stay cool. Key to this is the microsecond pulsing technology – a technology we have perfected for over fifteen years, beginning with our curing tools. No matter how much energy you bring in with a single pulse, you’re not going to process in one microsecond. Our patented technology ‘stitches’ multiple pulses together over a longer period, moving from the microsecond of a single pulse, to the seconds range needed for solder reflow. With this technology, printed electronics and microelectronics manufacturers can now attach components to previously off-limits, less expensive, substrates.

Significantly higher throughput over conventional processes, due to speed, and our broadband, wide area light source. This allows us to have spatial selectivity not only in the Z direction, but also in the XY direction. This capability addresses a crucial challenge in the SMT process: controlling the Delta T, across either the X, Y, or the Z direction. Additionally, while our PulseForge Soldering In-Line is suited for low-mix, high-volume, high throughput processing, we also offer the PulseForge Soldering Batch, an R&D model tailored for very high-mix, low-volume needs.

Because conventional reflow processes are so large in footprint and slow in throughput, you generally have only one reflow oven per line. With the speed of PulseForge Soldering, you can have multiple lines coming into a single PulseForge Soldering tool. Not only is PulseForge Soldering 40% smaller than standard reflow ovens, but in terms of time, it could take 10 or more conventional ovens to do the job of one PulseForge Soldering tool. PulseForge Soldering takes the slowest part of the line and makes it the fastest.

If processing on a rigid substrate, such as FR-4, ceramic, or metal, tensile strength is the same that you’d expect from a conventional reflow oven. For flexible substrates, we are seeing that any negative result is not the solder joint, but the adhesive that connects the tracks to the flex circuit. Because of the operator’s ability to control the pulses, they have excellent control over the peak temperature, and how long to keep at peak temperature. That allows for extremely precise control over the thickness of the intermetallic layer. And because cooling begins the instant the light is off, and energy sources taken away, the tool does not stay hot. Rapid cooling means microstructures become very small, and that creates a lot of tensile strength in the joint.

We recognized that there are a handful of major manufacturers of solders, and a narrow family of their solders that are used by nearly every manufacturer. We met with those manufacturers and qualified those specific, widely-used solders. Through these relationships, we are also exploring any additional solders that are optimized for our process. We are also working with a wide variety of solder alloys. PulseForge Soldering reflows with off-the-shelf SAC305, a very popular and widely-used solder.

With the support and expertise of our inks team, we are actively working with low temp solders, and are seeing very good results. We’ve also seen good results with the low silver-content SAC alloys, like SAC105, and have been able to qualify those and provide them to our customers.

Safety of all of our tools is of paramount importance to PulseForge. At its peak, the amount of light energy our proprietary technology is putting down in one microsecond to the hundred microsecond timeline, is more than half a million suns shining simultaneously. An extraordinarily bright source. There are multiple safety interlocks on all PulseForge tools, as well as an abundance of light shields in both the PulseForge Soldering In-Line and Batch tools. And because of multiple, internal moving parts, E-Stops are at arm’s length, and easily reachable from any location on the tool. PulseForge tools have all global safety certifications, meeting the strict requirements demanded by individual countries, including Germany, Japan, and China.