The most important and difficult aspect of PCB designs using 0.3 mm ultra-fine pitch BGAs is the layout of their lands and fan-outs. PCB lands are where device balls sit and get soldered to. Fan-outs are traces from the device lands to adjacent via. A via is required to distribute the I/Os, powers and grounds from the device to the peripherals and typically there is one via per land, as shown in Fig. 1.
When it comes to 0.3 mm ultra-fine pitch, there can be mistakes and erroneous thinking at PCB layout. Thatís when the designer innocently uses 0.5mm pitch design rules of thumb, which can have adverse effects on board fabrication and assembly. A wide range of issues arises in those areas to include problems associated with stencils, solder paste, and pick and place, among others. In particular, the designer must be aware of the current manufacturing capabilities in addition to the PCB’s electrical requirements.
For a more detailed account on the PCB layout and design issues when entering the 0.3 mm ultra-fine pitch BGA arena, check out our embedded.com article.
But for now, here are some key tips to help you avoid potential problematic areas:
- For sure, check out your contract manufacturer (CM) or EMS Provider to get assurances theyíve got a head start and experience dealing with ultra-fine pitch BGAs.
- Determine whether or not the PCB design group closely interacts with assembly/manufacturing engineering to anticipate and resolve potential issues dealing with land sizes and solder mask openings for example.
- Get a solid understanding of the pros and cons dealing with non-solder mask defined (NSMD) and solder-mask defined (SMD) pads.
- Carefully and methodically analyze with your CM or EMS Provider whether or not NSMD or SMD are best suited for your project.
- Understand that sometimes SMD is the better choice because it allows a slightly greater solder area on the BGA pad and solder shorts are less likely.
- Keep in mind that the earlier 0.5 mm fine pitch BGA rules of thumb may not be effective at the 0.3 mm ultra-fine pitch BGA level, especially when working at high volumes.
Lastly, via in pad may still be relatively new to many OEMs many have yet to venture into ultra fine pitch BGAs and CSPs. In those cases, those designers are still using conventional dog-bone fanouts. However, once OEM system designers move into ultra fine pitch devices and deploy via in pad, they’ll realize the technology helps reduce parasitic inductance, as well as increase density. Density increases because the via is directly placed under the device’s contact pads, and at the same time, routing is improved.