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We asked for you to send in your questions for Happy Holden, and you took us up on it! The questions you've posed run the gamut, covering technology, the worldwide fab market, and everything in between.
Here is a question that relates to a topic near and dear to Happy's heart: improving connectivity.
Q: There are usually several ways to improve connectivity on any board (including HDI boards). But are there any general principles for which order these features should be added to achieve the best results?
A: From a connectivity and density improvement standpoint, the use of blind vias (either drilled or lasered) offers the greatest gain, especially since the pitch of active components that drives density is shrinking. Next is the reduction of the diameter of via holes and smaller annual rings. Reducing traces and spaces comes next if you do not run into impedance and signal losses, and then blind vias. The final step is adding more layers.
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Douglas G. Brooks, PhD
Many design engineers and even many software suppliers make the significant mistake of equating changes in trace or via temperature with current density. This is incorrect at best and dangerous at worst. There is little if any correlation between temperature and current density. Current and trace dimensions (among other things) are the relevant variables, but current density is not. I hope by the end of this article you will see why. Here are four illustrations that will help you understand this.
Christian Keller, Altium
PCB developers are deluged with new challenges caused by increasing density and smaller components. Ball grid arrays (BGAs) create particular challenges during layout, with hundreds of connections in just a few square centimeters. Fortunately, designers now have options for addressing these issues.
Craig Armenti, Mentor
A key aspect of HDI technology is the use of microvias. For reference, the IPC HDI Design Committee has identified microvias as any hole equal to or less than 150 microns. Multiple types of HDI stack-ups associated with blind and buried microvias can be used to meet the density and cost requirements for today’s products. Design teams should develop stack-ups in conjunction with the fabricator to minimize cost and meet signal integrity requirements.