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1. Create a net list file *.lst for any of your critical signals that need a backdrill process.
$ G# Z# f4 x' h. w3 t' {5 V: n+ y. F' v2. Assign the BACKDRILL_MAX_PTH_STUB property(value=12mil) by using Edit – Property in Allegro PCB Editor. Alternately, you can specify the BACKDRILL_MAX_PTH_STUB property in the constraint 3 h1 `! r4 K8 M) ]0 z
manager. Actually, this property is the most important aspect among all the setups in order to enable the new backdrilling functionality.6 S' e4 L$ Y7 ~2 C# u
(3). Exclude certain objects(symbol,pin,via) in a net from backdrilling, such as all pins on a solder tail connector. As a soldered connector may lose its ability to be soldered to the board if the hole barrel is* s1 C. U& k+ r+ `% [4 q: H
drilled out. Symbols, pins, or vias with the BACKDRILL_EXCLUDE property are ignored during stub calculations and backdrilling analysis.) u& z% ?* @1 T" K; C
All related properties are defined as blow:6 J3 ?# v* n! P
Backdrill_exclude (symbol,pin,via) To exclude symbol,pin,viafrom backdrilling.
1 R' E0 {% p- Q$ d7 X LBackdrill_override (symbol,pin,via) To ensure backdrilling always occurs for specific objects to user-defined layer spans.
1 i( \/ J6 }0 E! |# a. N: ]/ VBackdrill_min_pin_pth (symbol,pin) To ensure the backdrill depth does not violate the minimum plating rules you specify. You can control how much vertical depth is required for a pin to be plated properly.
}9 O: }! |5 D9 K% Z+ YBackdrill_pressfit_connector (symbol) To ensure the pressfit-connector can be backdrilled from both board sides with respect to their contact range in the plated thru hole.
/ M6 P0 `+ v' z(4). Setup the padstacks and the constraints correctly to ensure the hole to etch clearance greater than 20mils.2 B' h! W2 L5 n. r4 J
Furthermore, as for the BGA area with pitch like 0.8mm and 0.65mm, we sometimes need to do some compromise of the principle, we have to work with the hole to etch clearance like17mils, but please make sure check with the fab house first on this point before you proceed with it.
! x) A8 R" \ x% b" c(5). The Pass Sets Backdrill Setup
7 I+ i t; [# s0 x, LAs a default setup of the Backdrill Setup and Analysis dialog box, you will see two pre-seeded rows(Pass Sets) enabling backdrilling to be performed on all objects, from either side of the board, and to all layers necessary to completely remove the entire stub regardless of the value assigned to the BACKDRILL_MAX_PTH_STUB property. Essentially if using the Cadence defaultpasses, you allow the software unlimited bandwidth to completely remove the entire stub of nets assigned the BACKDRILL_MAX_PTH_STUB property. Because the backdrill process is charged based on the numbers of Pass sets you are going to use. If you want to lower the cost, you can use less pass sets as longas the max stub length requirement allows, that means you can have specific requirement on the backdrill begin&stop layers. You can setup custom Pass Sets by inserting new Pass Sets and enabling them as well as disabling the pre-seeded rows. However, please be aware that only the one you setup in the dialog box will be present when creating the drill table and then will go through the backdrill process when fabrication in the fab house.9 r/ W- ?2 I, c! ], |: D' r
6. Analyzing Backdrilling Results7 G( F2 K# R( A' i
You can generate the backdrill_analysis.log report detailing backdrill data by clicking Analyze on the Backdrill Setup and Analysis dialog box. This preview lets you evaluate the backdrilling impact of enabled pass sets definitions.+ e$ p; |6 p( l6 l
7. Using Backdrill Legends
1 k: N- s& L( K2 ?( [' p. H' v, AWhen you choose Manufacture –NC –Drill Legend, you need to enable the Include backdrilloption on the Drill Legend dialog box to create backdrill legends. For backdrill legends, an NCBACKDRILL-<L1>-<L2> subclass generates on the MANUFACTURING class, in which <L1> indicates the from-side layer number; <L2>, the to-layer.
8 j1 R3 w! G6 x N* W% a {" k8 kThe items (3),(4),(5) are optional steps. Please beaware that not every project needs these steps |
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发表于 2015-5-11 11:14
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发表于 2021-9-11 13:58
roperties给需要背钻的网络设置BACKDRILL_MAX_PTH_STUB属性；3 h b3 Y: Z) J+ R% c
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