Tape and Reel Solder Preforms: A Success Story for the UD00 X86 SECO Board

Estimated reading time: 3 minutes

SECO's latest product innovation, UDOO X86, is a real computer with an integrated Arduino 101 compatible board that is capable of running games and videos in 4K. In short, a board destined to revolutionize the technology available to product designers seeking to strengthen the connections between computers and daily life. The UDOO X86 is 10x more powerful than the Raspberry Pi 3, which is the world’s most commonly used single board computer. Additionally, the UDOO X86 is compatible with all major operating systems (Android, Linux and Windows), which allows this small board to be used with all types of software, and in the most diverse operating environments.

Through a community of developers and managers who collaborate online to widen its potential applications, the technology of the UDOO X86 is paving the way for new developments in software connected to household sensors, such as switching off lights for example.

The success of the UDOO X86 is impressive, but so is SECO's ability to develop this game-changing product with low-cost technology for mass appeal and affordability.

The Design Manufacturing Process

In designing the hardware of this board, aimed at a huge audience of electronics enthusiasts, SECO had some major challenges to address:

1. to simplify the process in order to substantially reduce costs
2. to guarantee the superior mechanical strength of the product and all of its soldered joints
3. to guarantee the product’s electric and electrochemical reliability

The board has three connectors, with 12 PTH pins, which would conventionally be wave soldered or selectively soldered. To simplify the process, the decision made was to remove a step of the process to achieve cost reduction benefits. Initially, the focus was on eliminating the wave process, and replacing it with pin-in-paste soldering technology. This possibility was investigated and successfully trialled, but it did not entirely solve the other two major challenges mentioned above. First, the strength of the solder joint could not be improved because the maximum quantity of paste applicable with the pin-in-paste technique would not be sufficient to fill the hole in compliance with the IPC-610 Class II standard. Secondly, the pin-in-paste solution deposits a considerably higher quantity of flux than required, which creates potential risks to electrical reliability. In fact, considering that solder paste has a 50% metal content, it is often forgotten that this percentage refers to weight, but the situation is completely different for volume, as visually represented in the following diagram.

Diagram 1: The solder paste’s 50% metal content refers to the weight of the metal.  

Ultimately, the solution proposed by Alpha engineers, in collaboration with the SECO team, was to implement Solder Preform Technology. Solder preforms are small shapes of solder alloy that are designed to add solder volume and improve reliability where conventional soldering methods fail to give satisfactory results. The solder preforms used for the UDOO X86 board were ALPHA Tape and Reel 0402H size preforms that could be easily placed on the board using a standard pick and place machine common to all SMT lines.

A detail of the board layout can be seen in Figure 1, which highlights the two connectors.

Figure 1: Connectors shown on UDOO X86 PCB.

In addition to 10 SMT pads, there are 14 classic “holes” for wave or selective soldering. Figures 2 and 3 show the appearance of the board after the screen-printing process and the positioning of the preforms.

Figure 2: PCB after screen-printing process.

Figure 3: Preforms shown in position.

As Figures 2 and 3 suggest, the preforms must be in contact with the paste for two essential reasons: (1) they must be held in position; and (2) they must be reflowed using the flux contained in the solder paste, which is more than sufficient. Additionally, it is not absolutely necessary for the preforms to be immersed completely in the paste. In fact, as seen in Figures 2 and 3, only a minimum of 20% of the preform must sit in the paste deposit. During the reflow process, the molten alloy of the preforms is entirely drawn into the hole. It has also been proven that there is no risk of short circuit, even though the preforms are so close to each other.

To read the full version of this article, which appeared in the May 2017 issue of SMT Magazine, click here.