AltiumLive 2017: Effective Methods for Advanced Routing Charles Pfeil Senior Product Manager Dave Cousineau Sr. Field Applications Engineer
Charles Pfeil Senior Product Manager Over 50 years of experience in the PCB design and software industry. Designer and owner of service bureau. Worked for Racal-Redac, ASI, Cadence, Intergraph, VeriBest, Mentor Graphics, and now Altium. Architect of products with automation that gives the designer control, quality results, fast performance. Holder of 11 patents. Wrote a design book titled, "BGA Breakouts and Routing". Inducted into the PCB Design Hall of Fame by the UP Media Group. 2
Agenda 1 Routing Problems 2 3 Techniques Breakouts Fine Pitch BGAs 4 Quality 5 Rules 6 Differential Pair Routing 3
Routing Problems Routing can be difficult and time consuming Dense board area and limited layers Before increasing layer count, consider alternatives River routing, via-in-pad, stacked µvias Reduce trace widths, use thin dielectrics High-speed concerns Manage all concerns based on edge rates and data rates Timing Use realistic tolerances, tune gaps. Driver compensation? Crosstalk Manage clearance to aggressor relative to reference plane Impedance Realistic management of the appropriate concerns 4
Routing Problems Additional routing difficulties Over-constrained rules Can make design needlessly complex unnecessary rules don t improve the design Compromise in the right places identify problems and review with engineering early Fabrication requirements Know your fabricator s capabilities clarify discrepancies at the beginning of the design Create templates based on fabricator and via technology used. Investigate if HDI can be lower cost HDI Handbook, Happy Holden presentations The art of PCB design is discovering and applying the suitable compromises that enable the circuits to work as desired, while meeting the time and cost budgets. 5
Agenda 1 Routing Problems 2 3 Techniques Breakouts Fine Pitch BGAs 4 Quality 5 Rules 6 Differential Pair Routing 6
Routing Techniques Improved routing software enables productivity Take advantage of automation Does it allow designer control? Does it produce manual quality? River routing Reduce vias, manage impedance Gloss & Retrace Better diff pair quality, even over manual route Pad entry, change width gap 7 Interactive routing tools continue to increase levels of automation.
Routing Techniques Improved routing software enables productivity Copy & paste Simplifies fanouts and makes them consistent Use a grid! Factor of pin-pitch, reset origin to pin Pin swap Can make routing much more direct, less layers Keyboard shortcuts Learn the shortcuts, use them Create a list of the ones you use the most 8 Automated interactive routing tools increase productivity with user control and quality.
Agenda 1 Routing Problems 2 3 Techniques Breakouts Fine Pitch BGAs 4 Quality 5 Rules 6 Differential Pair Routing 9
Breakouts Fine Pitch BGAs Breakout of fine-pitch BGAs Fanout & escape tracks for.65mm pitch Difficult challenge Will get worse as pin-count increases Via-in-pad methods Best approach Location of via can improve route density Reduce trace widths Thru-via vs µvia If pin-count high, need µvias or high layer count Today, stacked µvias is by far the best solution for very dense HDI designs. 10
Breakouts Fine Pitch BGAs Push perimeter fanouts If perimeter pins need fanouts, push away from BGA Can eliminate one escape layer for large BGAs Especially useful if there are power & ground pins on the outer two rows 11 Creating effective fanout patterns is puzzle solving that can increase route density.
Breakouts Fine Pitch BGAs Via in Pad VIP Pattern A µvia in the center of ball pad Via hole must be filled and smoothed Eliminates trapped air voids during soldering Route density may not be maximized B-C-D patterns may be better depending on pitch VIP pattern for.4mm pitch BGAs 12 Experiment with different patterns and find what is most effective.
Breakouts Fine Pitch BGAs Offset VIP Pattern B The µvia offset from center, still completely inside the ball pad May not need to fill & smooth µvia Likelihood of trapped air voids is much smaller than in the case of the A pattern. This Offset VIP is optimal for.5mm and.65mm pitch BGAs 13 Patterns may be applied on the whole BGA or locally as needed.
Breakouts Fine Pitch BGAs Partial VIP Pattern C µvia hole intersects the edge of the ball pad Location determined by route density Maximize the number of traces that can be run through the channel between µvias µvia hole may not need filling & smoothing Work with fabricator and assembler Find out if not filling the µvia is supported C pattern good for.65mm &.8mm pitch 14 Route as much as allowed on outer layers, and push outer fanouts away from BGA.
Breakouts Fine Pitch BGAs Partial VIP Pattern C Partial VIP Inner Layers Increase the potential number of tracks running between the vias. Useful for critical signals, power and ground, diff pairs 15 Vertical channels may be blocked depending upon via and track sizes.
Breakouts Fine Pitch BGAs Near VIP Pattern D µvia hole completely outside edge of ball pad Soldermask opening concern Make µvia hole completely outside the soldermask opening for the ball pad Potential maximum density May enable the best alignment of the µvias in columns and rows for the greatest route density D pattern good for.65mm and.8mm pitch 16 Experiment, but make sure you discuss solutions with fabricator.
Breakouts Fine Pitch BGAs Near VIP Pattern D NEAR VIP Inner Layers Maximize the potential number of tracks running between the vias. Can be 25% greater space than Partial VIP 17 Take advantage of pins that don t need fanouts and consider them in patterns.
Breakouts Fine Pitch BGAs 0.65 mm BGA - VIP 300 µm Ball Pad 100 µm Trace 180 µm µvia 18
Breakouts Fine Pitch BGAs 0.65 mm BGA - VIP 300 µm Ball Pad 100/75 µm Trace 275 µm µvia 19
Breakouts Fine Pitch BGAs 0.5 mm BGA - VIP 200 µm Ball Pad 100 µm Trace 200 µm µvia 20
Breakouts Fine Pitch BGAs 0.5 mm BGA Offset VIP 250 µm Ball Pad 75 µm Trace 200 µm µvia Better than VIP 21
Breakouts Fine Pitch BGAs 0.4 mm BGA VIP 180 µm Ball Pad 75 µm Trace 180 µm µvia.35 mm BGA Same approach as.4 mm But smaller feature sizes 22
Breakouts Fine Pitch BGAs 0.4 mm BGA Offset VIP 180 µm Ball Pad 75 µm Trace 180 µm µvia Worse than VIP Fewer total tracks VIP = 1 per channel Offset VIP =.75 23
Agenda 1 Routing Problems 2 3 Techniques Breakouts Fine Pitch BGAs 4 Quality 5 Rules 6 Differential Pair Routing 24
Route Quality Quality is about routing efficiently and meeting requirements Efficiency - Reduce meandering, vias, route segments Makes it easier to edit later Signal behavior requirements Symmetry looks nice, but avoid enabling crosstalk A design that works is the #1 priority Fabrication recommendation: Space is King Use automation that improves quality I certainly appreciate artistic work, but 25 An artistic appearance is a result, not the cause, of quality design.
Route Quality Quality is about routing efficiently and meeting requirements Efficiency - Reduce meandering, vias, route segments Makes it easier to edit later Signal behavior requirements Symmetry looks nice, but avoid enabling crosstalk A design that works is the #1 priority Fabrication recommendation: Space is King Use automation that improves quality I certainly appreciate artistic work, but 26 An artistic appearance is a result, not the cause, of quality design.
Agenda 1 Routing Problems 2 3 Techniques Breakouts Fine Pitch BGAs 4 Quality 5 Rules 6 Differential Pair Routing 27
Rules To ensure success, properly constrain the routing Use the rules for DRC and control Avoid wantonly ignoring rules Automation can make it easier Simplify the rule definitions Avoid over-constraining 28 Appropriately defining the rules makes routing and editing easier and faster.
Rules Over Constraining Conservative data sheets Skew budget (length tolerances) often in unnecessarily small Why? Desire to eliminate possibility of potential problems Finding the right balance of compromise Often not possible to over-constrain everything without sacrificing one or more of these: cost, time, size, performance or reliability Design Software If the software enables you to easily address the over constrained rules, why not use it? Allows the margin (available skew) to be reserved for other effects 29 Over constraining a design may result in more layers and higher cost.
Rules Over Constraining The truth Rick Hartley s presentation The Truth About Differential Pairs in High Speed PCBs illustrates that over constraining differential pairs may not be necessary Rick s view on differential pair length tolerance based on circuit speed 30
Rules The other side of the coin If it isn t broke, don t fix it Organizations continue conservative design practices simply because they worked in the past Reluctance to analyze constraints to determine if they are really necessary Pushing the envelope Continually strive to make process more efficient and effective Most important question At what data rate can a particular diff pair concern become significant and how is it to be managed? 31 Analyze constraints and solutions to reduce time to market and fab yield
Agenda 1 Routing Problems 2 3 Techniques Breakouts Fine Pitch BGAs 4 Quality 5 Rules 6 Differential Pair Routing 32
Differential Pair Routing Addressing concerns based on data rates 33 Know the problems & solutions Manage the primary concerns Timing, impedance, crosstalk Avoid over-constraining Reasonable tolerances Auto compensation Allows for greater timing margins Pad entry Converge ASAP with equal length
Differential Pair Routing Diff pair may be shorter due to faster propagation Avoid Creepy Lengths when the target length keeps growing if routed in positive tolerance In length matching, include via-used and pinpackage lengths Tuning compliments together results in no skew difference, it is always balanced Rick Hartley s Truth About Diff Pairs Diff Pair 3xH Aggressor H Reference plane 34 To prevent crosstalk on diff pair Corner and pad entry skew adjustments
Differential Pair Routing Corner Pad Entry Keep stitch vias equidistant to DP vias Phase match start at driver, bump at mismatch Fiberweave routing If loose weave makes one compliment is over glass and the other over resin 35 Search: Jeff Loyer fiber weave effect Best presentation on topic
Differential Pair Routing Impedance discontinuities can cause reflections which may add noise to signal Cannot avoid all of these discontinuities, so try to minimize the number of them 36 It is simply a matter modifying the routing to keep the same impedance, with reason
Differential Pair Routing 37 Remove stubs with backdrilling Eliminate stubs with µvias
Differential Pair Routing Using arcs When does it matter? When the data rate is >16Gb/s everything matters 38 Arcs are beautiful, but usually not necessary
Differential Pair Routing Pad entry Converge ASAP with equal length This will help to eliminate skew at the start and end of the routing Pad entry gloss may work well Fabrication concerns Teardrops, etch traps, soldermask Balanced pad entry Very Good Usually Within Tolerance 39 Pad entry is a good example in which automation can make routing a lot easier
Conclusion Routing tools and methods are improving: Tools continually enhanced for new circuit, component and fabrication technology New methods with effective automation can increase productivity and quality Using the available skew for each circuit will increase productivity Avoid over-constraining and making routing easier, yet still effective 40 Get the most out of the available automation for routing.
DRC Checklist Check Priorities for all rules Ensure that All-All Width and Clearance rules exist Set to lowest Priority All used via sizes fall within Via Style Min and Max values Actual Class names match those in Class-scoped rules Class name = power vs. Rule = InNetClass( pwr ) All (or appropriate) Routing Layers are enabled Check applicability of more complex rule scopes using Test Queries button Ensure that necessary rules are enabled! 41 For Interactive Routing, set Width and Via sources to Rule Preferred
Thanks for your Attention! Questions?