Ask Me Anything with Happy Holden

Start posting your HDI questions now and Happy will answer on January 3rd!

Given your extensive experience, what trends do you foresee in the field of HDI PCB design and manufacturing in the coming years? How are these trends influencing the way designers approach HDI layouts?

Also, any new books coming up?

Sierra is delving into the realm of Ultra High-Density Interconnect (uHDI) PCBs. Happy, what are the distinctive challenges and considerations that our designers should be mindful of when working on uHDI designs? Additionally, are there any specific design strategies or manufacturing techniques that you find particularly effective for achieving success in uHDI projects?

I’ve encountered challenges related to microvia reliability in my HDI designs. Happy, could you provide insights into common issues with microvias and any strategies to enhance their reliability during manufacturing and operation?

Are there any new or innovative materials that you recommend for HDI designs?

I’m interested in learning more about via design in HDI, especially when it comes to stacking vias. Could you provide insights into the optimization of via structures for both signal and power integrity?

Could you share your recommendations on testing and validation strategies for HDI designs? Are there specific methodologies that you find particularly effective for ensuring the reliability of HDI PCBs?

Because ICs are becoming more complex-and HI/chiplets is progressing, HDI and U-HDI use will be expanding. This will introduce new materials not normally used in HDI PWBs & this will affect design rules. Also new architectures like VeCS lower HDI costs and improve reliability. This trend will continue-so continuous education is the rule!

1 Like

Ultra-HDI for PWBs is relatively new for North America. But I have worked with it for 20 years in Asia. The KEY to successful design (ie HIGH YIELDS) is a close working relationship with the fabricator. U-HDI uses NEW materials that we have not used in N.A. and as fabricators perfect their processes, these dictate design rules and stackups that can differ a lot from fabricator to fabricator. So pick a fabricator and a ‘TEST VEHICLE’ and work closely with them-soon we will have some new IPC Standards that will help standardize U-HDI but it will still be a ‘Wide-open-technology’. I will cover some of these design strategies next week (Jan. 10) on the Sierra Webinar.

George-you are NOT unique on this problem. This will be the main theme of my Sierra Webinar next week (Jan 10 at 10:00 AM pst). In short, microvia design should start with a Reliability Test Vehicle and then progress to the microvia board design! An OEM needs to be able to trace each lot of microvia boards fabricated to the fabricators process and material control,AND test the reliability annually with a Benchmarkable Test Vehicle.

The only NEW HDI material (other than all the new HF materials w/spread-glass) is the polyimide/epoxy RCC and the reinforced RCC films. But for Ultra-HDI, there is a WHOLE LOT of new materials from Asia finally coming to N.A.

This is an important design topic but too complex for a simple reply. The best written to-date is from the EU Space Agency and presented the last 2 years at the IPC-APEX and in some of the PCB007 APEX reports. They tested several HDI stackups & design rules and then did extensive reliability testing on the resultant TV Coupons (4 types).

The last 2 years at IPC-APEX the HDI sessions have been ‘standing room only’ and it has been about Design rules, materils and testing/validation. The 2 papers from the EU Space Agency and Lockheed-Martin talk specifically on Test Vehicles, the 4 methods of thermal testing and the follow up reliability validations.

I have a design with 0.45mm and 0.5mm pitch BGAs. I can escape from the inner pins with 3mil/3mil trace/space or use laser-drilled microvias to breakout on an internal layer.
What would be the impact to PCB fabrication lead time and cost to one or the other? I would not expect a specific dollar amount or days difference, but relatively speaking which is more difficult or time consuming in bare board fabrication fine trace and space, or adding microvias as a process to the design?

That is a good question-but one of three questions you must ask when considering using microvias. 1. Do I need uvias to breakout my components 2. Do I have closely coupled busses between parts (ie. CPU/cache) 3. Do the total interconnect/board routing area exceed the capability of my surface routing density (Wc). If you are already using 0.45 & 0.5 mm pitch BGAs then DENSITY is a factor in your designs. As long as your fabricator has good yields on 3mil/3mil t/s, then NOT using uvias will cost less and be easier to build. Unless one of these 3 questions indicate that the use of HDI is warranted. Download these three HDI Design Manuals are read the sections on “DO you Need HDI Design?”