[sdiy] Why transistors arent square!

[David G. Dixon]

I always figured that the shape of TO-92 transistors was a reflection of
their schematic symbol...?

David G. Dixon
Professor
Department of Materials Engineering
University of British Columbia
309-6350 Stores Road
Vancouver, B.C. V6T 1Z4
Canada
 
Tel 1-604-822-3679
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> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl [mailto:synth-diy-
> bounces at dropmix.xs4all.nl] On Behalf Of karl dalen
> Sent: Monday, February 16, 2009 12:40 PM
> To: Tim Parkhurst
> Cc: synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] Why transistors arent square!
> 
> I still cant se your argument that the halfsphere are cheaper?
> If you take a close look its not even halfspherish, its infact
> made of twho very different millings for the tvo mold pieces.
> The top is rectangular but has sort of slanting edges!
> 
> That mould design would be more expencier then a true half sphere
> as you sugest, then i could have agreed to your sugestion!
> 
> Another argument are that SMT came first , however it may be
> as you hint a tradition thing borrowed from the metal canned
> transistor era!?...... Yet its a drag! :)
> 
> Reg
> KD
> 
> 
> --- Den mån 2009-02-16 skrev Tim Parkhurst <tim.parkhurst at gmail.com>:
> 
> > Från: Tim Parkhurst <tim.parkhurst at gmail.com>
> > Ämne: Re: [sdiy] Why transistors arent square!
> > Till: dalenkarl at yahoo.se
> > Kopia: synth-diy at dropmix.xs4all.nl
> > Datum: måndag 16 februari 2009 00.05
> > On Sun, Feb 15, 2009 at 10:13 AM, karl dalen
> > <dalenkarl at yahoo.se> wrote:
> >
> > >
> > > 2009-02-15  Tim Parkhurst
> > <tim.parkhurst at gmail.com>:
> > >
> > > > My guess is that this is a very easy shape to
> > make a mold
> > > > for, and it's also
> > > > a VERY easy finished product to get out of the
> > mold.
> > > > Basically it comes down
> > > > to manufacturability. Molding technology has
> > improved over
> > > > the last few
> > > > decades, but the half round is still a very
> > simple thing to
> > > > make. It might
> > > > also have a slightly larger outside surface area
> > (helps
> > > > cooling).
> > >
> > > Nope, there are sot23 devices with worser spec
> > who's more costly
> > > then TO92's so the molde are no issue to the end
> > cost of the product
> > > at these levels. It's a managing problem,
> > conservative managers destroys
> > > products and markets just because they want to feel
> > important and
> > > want to flux their prestige!
> > >
> > > KD
> > >
> > >
> > Yes, SOT23 packages are rectangular, but remember they:
> >
> > 1 - were developed several decades later, when the molding
> > technology has
> > improved and decreased in cost a great amount.
> >
> > 2 - are much smaller, and don't have the same style of
> > leads.
> >
> > 3 - are designed for placement with automated equipment.
> >
> > In short, I think the half round package was probably the
> > best choice at the
> > time (1960s / 1970s), and this packaging style has
> > continued until today out
> > of tradition (although it may also be that the half round
> > is still a very
> > inexpensive package to manufacture). Modern SOT packages
> > are rectangular
> > because it's economically viable to make them this way
> > and, most
> > importantly, because SOTs are designed to be placed with
> > automated
> > equipment. I'll agree that there could well be egos and
> > personal agendas in
> > play when decsions are made, but I'd like to think that
> > most engineers would
> > chose a certain design because it works better and/or is
> > significantly less
> > expensive.
> >
> > Tim (round peg / square hole) Servo
> > --
> > "A nation cannot prosper long, when it favours only
> > the prosperous." -
> > Barack Obama
> 
> 
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