SCR layouting style probelm

[hslsc311]

hello ,everyone
i am layouting a SCR for ESD protection,but i am not sure about the location of P+ and N+ as shown below.in Fig1,inside the N well ,P+ is on the left,but in Fig2,inside the N well,P+ is on the right.
i wonder if the scr can be triggered if P+ is on the right since it is not on the current flowing path which is from right to left.both Fig1 and Fig2 are refered to on different books, i dont know which is right,or they are all right?
could anyone help me plz???

 

[dick_freebird]

There's a lot more to getting a good SCR layout, than the
2-D view. Particularly important is that you are trying to
make a GTO-SCR (gate turnoff). That means your gate
(base) contacts need to have absolute authority over at
least one of the BJTs, preferably the higher gain one (in
all likelihood, the well-base PNP).

This is the reason for putting the gate contacts inboard
of anode / cathode, so that they can "intercept" the base
current more effectively.

Now that will surely compromise the conduction qualities
of the SCR. But a clamp that won't turn off, is called
"latchup" and makes you no friends.

Fig. 1 will produce a better conduction. Fig. 2 will produce
a SCR that's easier to turn off with anode gate shorted to
anode.

But you also need to have control of the edges and the
fields at discontinuous points in the layout, which you
can't get a good sense of in the 2-D views.

 

[hslsc311]

thank you dick_freebird,i will reconsider it