1. On Routing Fixed Escaped Boundary Pins for High Speed Boards T. Tsai, R. Lee, C. Chin and Y. Kajitani Global UniChip Corp. Hsinchu, Taiwan DATE 2011

2. Outline Introduction Problem Formulation Routing under Fixed-Ordering Pin Locations Length-Constraint-Aware Routing Refinement Routing Results Conclusion

3. Introduction Current CAD tools for board routing are very few and cannot provide automatic solutions on board- level routing. Address a different yet practical problem: route the wires or busses on the board with the fixed components boundary pins.

4. Introduction Board routing is divided into two parts:  Escape routing  Area routing area routing

5. Problem Formulation Given:  The placement of the components on the board  The pins are fixed by package providers Objective:  Obtain a planar topology for all the connections in pin pair routing  A refined routing with length-matching constraint awareness

6. Routing under Fixed-Ordering Pin Locations Static Net Ordering with Dynamic Pin Sequence  Use a number sequence to represent the relative position of pins on one component.

7. Routing under Fixed-Ordering Pin Locations With components transforming to pin-sequences, concatenate those sequences into one sequence (Dynamic Pin Sequence). 1 2 Component 1: ANMLKJIHGFEDCB Component 2: NABCDEFGHIJKLM Component connecting point (CCP): K When choosing component 2 as a basic sequence: DPS: NABCDEFGHIJKKJIHGFEDCBANMLLM

8. Routing under Fixed-Ordering Pin Locations Net ordering

9. Routing under Fixed-Ordering Pin Locations

10. DPS: AACCHIIHEFEF DPS: HHEFEF DPS: EFEF Net order: BGDACIH EF (put to another layer)

11. Routing under Fixed-Ordering Pin Locations Against-the-wall topological routing  By using routed nets as boundary of routing space, the routes walk against the wall/boundary.  If there exist blockages, the direction will be modified to walk around.

12. Routing under Fixed-Ordering Pin Locations Handling the crossing nets  A case which has inevitable net crossing in planar routing.  Choose the net that will cause the largest number of crossings in the current layer and assign it to another layer.

13. Length-Constraint-Aware Routing Refinement The adjusting order follows the reverse order of against-the-wall routing sequence. Use a number sequence to represent the net segments.

14. Length-Constraint-Aware Routing Refinement Additional costs for each segment are evaluated to determine which segment are suitable for length adjustment.  Favor the shorter segments to be moved since longer segment wires are harder to adapt with the length adjustment.  More free segments get higher priority to be moved.  If other neighboring segments have no free space to move, the targeted segment is hard to be moved as well.

15. Length-Constraint-Aware Routing Refinement During the segment shifting process, use the following terms to control the net length:  Average of total net length (Avg) among the set of nets.  Length difference (Diff): the absolute difference between the certain net and the length average.  Matching ratio (Range = |Avg – Diff|/Avg) should be higher than 95%.

16. Length-Constraint-Aware Routing Refinement The segments with costs for shift priority are put into a shifting-list which records the order of shifting segments. A segment is chosen to be moved in the adjusting area. The adjustment must follow the constraints which refer to the length average, length difference and matching ratio. If the moving segment finishes shifting, it is removed from the shifting-list. We will stop if there is no improvement of the net shifting.

17. Length-Constraint-Aware Routing Refinement An example of net shifting  The net shifting process is applied until the original head is overlapped with the new head or the original tail is overlapped with the new tail.

18. Routing Results

19. The routing result of Test Case I.

20. Routing Results The routing result of Test Case III with and without obstacles.

21. Routing Results The routing result of Test Case III with obstacle by [4].

22. Conclusion This paper proposed a board router under fixed- ordering boundary pins. Their approach considers length-matching requirement and can utilize routing resource very carefully.