[chbot] CHCH creative space this Sunday

[Andrew McDougall]

True, You might get lucky and find some. But the app notes tell you how it is done. 

 

http://www.vishay.com/docs/53044/epicappn.pdf

 

From what I can see you want a small resistor – they use 0603

You need a element that can get to 400oC – they use Ta2N, they also list other possibilities. A bit of trial and error with different metal films maybe in order

Take the protective coating off

Calculated the current and time needed – equations below

 

The Heating Resistor

is a very precisely patterned Ta2N block which dimensions

are:

Length L, width W and thickness T.

The ohmic value is controlled by the resistivity of Ta2N and

by L, W and T.

R = (r x L)/(W x T) (1)

The electrical energy is also controlled through R

E = R x I x I x t (2)

The electrical energy is transformed into heat and the

adiabatic heating of the resistor comes from the following

equation:

E = m x c x ΔT = L x W x T x d x C x ΔT (3)

density d and specific heat C are Ta2N physical constants,

providing Ta2N deposition is perfectly under control.

Let us consider standard dimensions L = W = 50 μm,

T = 2 μm, then per equation (1) R = 2 Ω

Assuming that we want a 400 °C adiabatic heating of the

resistor the electrical energy E can be obtained from

equation (3).

E = 0.005 x 0.005 x 0.0002 x 16 g x 0.14 J/(g x °C) x 400 =

4.5 μJ

As a matter of fact and from some figures we have got back

from customers the actual electrical energy which is

necessary to fire up a critical mass of pyrotechnical material

is about 2 to 10 times the level of energy which is necessary

to heat up the resistor alone by 400 °C.

In our case, and in the worst case, a 50 μJ energy firing pulse

will be convenient. 

From equation (3) one can calculate the combinations R, I, t.

With R = 2 Ω

I = 1 A, t = 25 μs

I = 0.7 A, t = 50 μs

I = 0.5 A, t = 100 μs

 

 

 

	 

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