Solder jet printing – the natural evolution for microelectronics

EMS companies who produce PCBA’s have been using stencils for decades, to apply solder paste to boards, but this traditional method may one day be a thing of the past. Adam Harsant, Director at advanced CEM Gemini Tec explains why his company is at the cutting edge of technology with solder jet paste printing technology.

At Gemini Tec, as in every subcontract manufacturing company, each new product introduction starts with design specifications and a data pack that details all of the physical attributes of the PCB assembly. As appropriate, the company can provide layout expertise using Altium design tools or simply import the customer's ODB++ data.

So far, so ordinary, but thanks to the Mycronic MY500 & MY600 solder jet printers Gemini Tec acquired in 2008 and again in 2014, the journey from this point to the start of the manufacturing process takes under ten minutes, which is a far cry from the several hours or even days that will be expected with traditional stencil printing techniques.

With stencil printing, before production can start, the stencil has to be carefully engineered and often with a compromise and then manufactured from an external supplier. A production operative then has to take time to physically set up the stencil, solder paste and printer. And even then, the stencil printing process has significant limitations, in part, due to the ever-decreasing pad geometry found on today's compact PCB designs.

Controlling the amount of solder paste applied on a pad-by-pad basis is, for example, almost impossible and, with "difficult" components, this lack of control often means the yield through production is reduced. Its then commonplace to re-work boards manually, which drains valuable time and resources, with impact on production costs for the CEM and inevitably the end user.

By contrast, solder jet printing allows total control over the amount of solder paste deposited on each and every pad. Thanks to the way it builds up solder volumes with microscopic single dots of paste, jet printing ensures total consistency and creates the possibility of 3D solder build-up – with almost no limitations regarding keep-out areas. When a PCB designer places a 0201 next to a D-PAK, it's never been easier or more precise to position the correct volume of paste onto the board.

Using the jet printer is straightforward. The user sets the default volume for each solder pad based on CAD data, and can then fine-tune the deposit, on a pad-by-pad basis in terms of volume, position, and height of the paste. Built-in process controls take care of the rest, with no operator intervention required. The preparatory work can be performed offline, and all settings are saved for future use.

In comparison with screen-printing techniques, solder jet printing allows manufacturers to respond much more rapidly to customer demands and changes while achieving superior accuracy for every solder joint. There's no time wasted ordering, changing, cleaning or storing stencils, and far less risk of human error due to the reduced need for operator intervention.

As well as saving time, solder-jet printing has many other benefits, not least when working with flex, flex-rigid or even warped boards, as board alignment and stretch are measured with advanced sensors and compensated for in real time.

For pin-in-paste components, three-dimensional solder structures can be printed above the hole, using the printer's software to automatically program the correct amount and shape for each pin. What's more, users can edit the amount of solder paste during production in real time, removing the risk of production downtime and delayed shipments for time critical orders.

Using solder jet printing technologies available today enables the electronics industry to access a comprehensive range of new design possibilities. It puts manufacturers in full control of every solder joint – from package-on-package and internal board cavities and more.

This means that PCB assemblers that choose to put solder jet printing at the core of their manufacturing processes can respond to customer needs much more quickly – a key benefit in today's fast moving and highly competitive electronics marketplace. In addition, the ability to make changes during the production process means that faults can be caught early and quickly corrected. This means fewer reject boards and less rework, leading to savings that go straight to the bottom line and reduce the cost of production to its customers.

The ability to produce difficult and complex surface mount assemblies with a high yield, but also with cost reductions in engineering charges has been a dream of electronics manufacturers for decades. Communications devices, embedded computers, instrumentation – are just a few of the market applications requiring rapid turnaround on complex designs that are right the first time.

It's easy to see why solder jet printing is replacing stencil techniques for the leaders in the sub-contract PCB assembly and manufacturing world, but why is it that there are still so many others who are yet to adopt this innovative technology?

Many companies argue that their small batches are not worth the expense of investing in a machine for jet printing PCBs, but in reality, solder jet printers are ideal for small and complex orders. Gemini Tec handles many low-volume orders with typical batch sizes ranging from 1 to 1000 per run. The MY500 and MY600 printers have allowed the company to deliver these in time and without fault, offering dependable products at excellent prices to many happy customers.

The significant capital investment cost is also daunting for some PCB assemblers and CEM's who believe that unless they are producing high-tech products they won't get value out of a solder jet printing machine. There is also a view that using rework and test operatives who the company already employs cost less in the long run. However, for those companies whose customers demand the highest levels of responsiveness and product quality, an investment in solder jet printing will, in reality, quickly pay for itself.

In fact, the quality of the finished product is another of the reasons that Gemini Tec uses solder jet printing, and the quality gain can quickly be seen in terms of the product yield. Consider just one practical example – that of a BGA device with an open circuit solder connection. This is can be a difficult fault to find and repair and it's also one that users of stencil printing regularly encounter. With solder jet printing however, this type of problem simply disappears.

Implementing responsive, reliable and repeatable production processes is the holy trinity for PCB assemblers and CEM's, since achieving this means that they can supply their customers with the products they need when they need them – irrespective of batch size. Gemini Tec believes that all of its customers should enjoy these benefits, which is why the company has so enthusiastically adopted the key enabling technology of solder-jet printing.