"Current Source"

This quarterly, subscriber-based newsletter is delivered in print version to Speeding Edge customers. The newsletter is an an adjunct to "Right the First Time, A Practical Handbook on High Speed PCB Design." The newsletter was created as a result of a number of requests for additional information as well as questions regarding some of the technical information contained in the book. The issues of the newsletters are designed to be 'living' documents placed in three ring binders that are readily on hand at designer's and engineer's desks.

Summary of Current Source Volume 3, Issue 3

This entire issue was devoted to one topic: Designing a PCB Stackup. Despite its importance in the overall design cycle, stackup design is a topic that often receives short shrift. Companies don’t want to take the time to do a thorough stackup design process or it is not viewed as important to the overall final product realization. PCB stackup design is the fundamental basis from which the rest of the design process moves forward.

This extended article begins with identifying the various elements in the stackup and their importance for the overall board design; a description of a typical multilayer PCB and the three methods used for creating a multilayer stackup (foil and cap lamination and blind and buried vias) and the types of signal layers used in a typical multilayer board.

This is followed by the various ways to stack the layers in a board and how to select an impedance for each signal layer. There is also a thorough discussion of the alternate types of laminates available and how to determine which laminate is best for a given type of design. This includes the various factors to take into account when selecting a laminate system; determining the proper laminate thickness and selecting the right glass weave style. Also addressed is how to select the proper copper foil thickness including trace resistance vs. foil thickness and width and skin depth vs. frequency.

Other important topics covered in this comprehensive article:

• Calculating and measuring impedance test structures
• Steps used in designing a stackup
• How to account for the resin that flows into adjacent signal and plane layers
• Commercially available tools used to create PCB stackups
• How to create stackup drawings for both a 22-layer daughter board and a switch fabric
• Creating stackups for 4-layer stack-ups including creating a stackup drawing for a generic motherboard

Pricing and Availability

"Current Source" is offered as a subscription for $60 per year or $20 per issue. The newsletter can be purchased directly off the company’s website, by fax at 707-568-3504 or by telephone at 707-568-3983.

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