2 contacts per connection

[franck]

Hi,

Maybe it's a reflex things for a lot of you layout guys and others but I would like to know how many people follow this golden rule on every connections?
I am not talking about digital. Anyway a digital with 2 contacts connections (I mean home made by hand) is surely better. Why? You tell me. Serious question it's the first time I have the opportunitie to ask to a lot of people at the same time.
Maybe this topic can be follow by a lot of others just to seat down and be back to roots!!

 

[flatulent]

Reliability is the main reason for redundant connections. Another one for connectors is reduction of vibration effects. In the old days where PC cards had printed fingers on the edge for connection to a socket, two adjacent connection pins were always put in parallel. This was usually the ones on opposite sides of the card.

 

[franck]

reliabiliity ... yes ... yield ... that's better in a industrial way speaking.
YIELD and yield and yield ... that's the first job of a layout guy and many nany namy many forget that. The silicium is not free!!

 

[Teddy]

In general it is reliability - on older technologies with no planarization the etching was not very uniform what led to "skipping" some contacts/vias.
I wold say that nowadays it is not a dange anymore since the processing got much better - but still 2 contatcs is used as a golden rule.

In digital where the layout is driven by size you can usualy find just 1 cont/via per connection. And those devices are reliable - therefore I say you are safe with just one.

In analog layout you should consider the contact/via resistance especially in case of higher current structures. To force DC 1 mA through a contact is not a greatest idea.

If you have space and want to have lower ohmic connection use more conts/vias.

Also - in older technologies you were allowed to use different size contact sizes 9not only square but rectangular). This was causing problemsduring etching since the bigger contact were etching more than the small ones. Again today you usually can create array of contact of the same size to eliminate such a issues.

 

[MLR67]

The rule "two contacts" is used only for probability purpose and by the way for Yield.T
he probability to have two contacts not open at the same time is lower than only one contact and when you have the choice three contacts is better (access resistor divide by 3).

 

[kapils1982]

The main reason would be reliability.

Also i think that having number of contacts decreases the parasitic resistance as all of them are in parallel.

 

[justin999]

dfm

 

[franck]

dfm????
What does it mean?
In fact nobody answer my quetion. I would like to know who do this ALL THE TIME?
Thanks for your reply about resistance, capacitance reliability, probability??? ... but I starting to know all of this.
And like every time I asked this quetion to technical people they just can't say yes or no because they don't follow this rule every time which has a huge impact on production.

 

[uncle_urfi]

Your question:

"... who do this ALL THE TIME?"

Answer : The guy whose job it is.

"... "how" to do it ALL THE TIME?"

Answer: Create contacts between various layers as predefined layout blocks and use them whenever you want.

There are various configs you can experiment with:

1)Two contacts, (slightly skewed 5%) for a straight layer to layer connection.

2) Three contacts (triangular 60deg equilateral) for a corner connection to two other connections.

3) Four contacts: to reduce resistance and improve current carrying capacity and to branch off to two or more connections.

Also if these contacts are at the end of a line, try increasing the area at the end by 5% to improve reliability.