all right everyone and good afternoon
or morning
depending on where you are located and
welcome to today's webinar
my name is mark Ms TaTan
I'm seeing your sales engineer here at dr solutions
on the line with me today is michael blitzes
and he will be presenting on common mistakes by
electronic design teams
this is part Ⅱ
of a two part webinar series on this topic
last week's webinar was who stood by Dr
kreg hillman who is ceo of drr solutions
that is readily available at dr solutions
com if you would like to go ahead and download that
addition to today's webinar
I just want to go over a few housekeeping items
before we get started here
so this webinar is being recorded
and like last week's webinar
we will be making it fully available at dr solutions
com but if you can't wait for
for a few days for this to be posted
at the end of the webinar there will be a slide
with my contact information
you can go ahead and reach out to me directly
and I would be more than happy to send it to you
in addition all lines are muted
except my line and michaels line
so we're not going
to be stopping the webinar to answer any questions
but if you have any questions during the course
of the webinar
we will be addressing them
after michael is finished with this presentation
which should be in about 45 minutes roughly
so if you would like to
there is a questions tab on your google to webinar
screen just click that tab
go ahead and write in your question
and I will ask it
directly to michael at the end of the presentation
so with that michael
why don't you go ahead and take it away
good afternoon everybody
like mark said this is the second part
of common mistakes by electronic design teams
just really quick
some background about dr solutions
we are one of the top 50 fastest growing companies for
this in this field
we offer a variety of services
everything from finite element analysis
failure analysis root cause investigations
circuit analysis
we can also do
test the spec we can design
mechanical test fixtures test coupons
so we are end to end quality and reliability
company
this 2nd part
is
regarding mechanical parts selection in the first half
Dr Hillman he went over
make for spy
sizing your box
with regards to thermal issues
you went over electronic component selection
de rating power sequencing
this part we're going to focus more on
mechanical part selection
probably just touch on the most common areas
where we see issues
perhaps the No.1
cause of issues that we see is cables and connectors
it's one of the most common
failure locations in
most electronic systems
and embedded systems of course
the primary read of
some issues we see
especially with
has to do with a red phosphorus
flame retardants and connectors
and in cable
over molds
we are seeing this more towards in the commodity type
cables and connectors
things that people will buy off of amazon or eBay
or dx com you know the ones where
you're not sure where they came from
just be aware
that some of those plastics
may contain red phosphorus and if you put them in a
harsh environment where there's a lot of heat
and moisture
after two to four years in the field we see that the
plastic has dissolved and asteria acid has leaked out
and corroded the contacts or
coop and traces on the board
so just be aware of that issue
so
it's best just to not
not expect those kind of connectors
well not or just be aware of who your supplier is
and what plastic they're using
there are some
simple dfr roles for connectors
your power and ground should be
separated from each other
it's just so you don't get ting
whisker formation between the two high potential areas
you should shroud your connectors
you want to avoid blind insertions
this is really critical with mezzanine style
boards where you're plugging modules down
you want to have alignment features
mo helpfully
it's most helpful to have those lining features
on the connectors
so that the user can feel
the two connectors aligning and pushing them together
you run the risk of bent pins or
busted connectors if the user or the assembler cannot
positively feel the alignment
you should always have some sort of retention
connectors that and cables
that are inside a box
should have some sort of strain relief
especially if you're in a vibration environment
also you don't want to use
connectors or cables that are not
typically used internally in a box
sometimes I'll see well we've seen where people use
ethernet connectors to hook modules together inside
an electrical device
those connectors are not meant to be internal
they do not handle vibration well
and you're just asking problems
so when you're doing your connectors
you're going to want to be selecting a type of plating
the most
least expensive is tin
more expensive of course is gold
gold is good for high speed digital connections
it's good for if you're in a cruise of environment
it's also good if there's some sort of motion going on
if it's like it's vibrating
if you pick a connector
from a well established or well known supplier
you probably don't even have to worry so much about
your material specifications
your mole your sand tech
your t e your phenol
they're all pretty good
they're all gonna have well defined
you know you're gonna be able to pick what
you know by part number what
thickness gold you have
if you go with a lesser known
supplier you're going to want to specify
your thicknesses just
to make sure that they're going to be meeting
those thicknesses
the other
choice you're going to have is pinch tin is great
tin works fine in a certain application
if
you'll see
10 plated connectors and a lot of your appliances
you're using these because
they don't have to go through as many insertions
and be either cheaper
so if you don't have to go through that many insertions
and it's more of a power
and high voltage style signal
tin works great
there are a few drawbacks you cannot use it above
100 degrees c
and you do definitely do not want to
mix your plating
so you do not want to mix a gold plated connector with
a or contact with a tin
plated contact
what happens with that
is the golden tin form of metallic inner metallic
together actually fuse a little bit together
and then if there's any motion they
it rips the
gold plating right off the connector and you get oxide
and it's pleased to early failure
so that's one portion now
you're also going to have to select
when you're doing a
iconic system you have to select
what kind of housing you're going to use it
whether or not you buy
housing off the shelf
or you're going to design a housing
I essentially have two choices
that being of a plastic housing or metal housing
with your plastic housing
there's a few design concerns which I'll go over
and your metal housing
there's a few other concerns that
probably should be aware of
also
probably the most area
of concern with the plastic housing
is your boss design
and that's because they tend to be
a failure point
primarily because they're not designed correctly
they're the most one of the more critical
portions of your enclosure
because there they hold everything together
they hold your board down
they probably sometimes will hold it the box together
primarily most
common mistake is
the inner diameter is too large
for the self tapping screw
if you're using self
thread forming screws
you gotta be aware of that
if it's a slippery or plastic
like polypropylene you're going to want
some pilot oil and see smaller
you also have to be careful that you take
draft into account when you're designing your boss
because the boss diameter should be around 1.8
2.5 the diameter of the screw
if you're right on the edge and say you're at two
and you don't take a draft into account when you
send your plastic housing to be
the designs to the molding house
and they design the tool
they may add draft to all
the external surfaces
and you could
end up with a boss that's too narrow up at the top
in which case it'll crack easily
some other common issues
you need to make sure that the
thread engagement is sufficient enough
especially with the thread forming screws
sometimes you'll observe a thread forming screw
you may use a brass insert
in the boss
the key with the brass inserts in your boss is that
you want to make sure
that the bearing surface that's being
screwed down onto it
is against the brass and not against the plastic
if you don't made up against that brass surface
what happens is
the screw actually pulled
the brass insert out of the plastic
and this is called insert jacking
so I've got a
couple images on the screen
of what is a good
installation and what is a poor insert installation
the one that's as bad
you'll see that the insert is actually
suppressed down into the hole a little bit
so what's going to happen is as you tighten that up
it's going to get pulled up
and that will cause it to become loose
another issue of concern with plastics is not
sensitivity
this really just comes down to making sure you have no
really sharp
interior corners
the more durable plastics
like your acetates or your decline
and some of your polycarbonate
and also if you have a
high mineral load
in your plastic which is made it really stiff
this becomes critical
for example the piece I show here
was made out of the seattle
which is almost as strong as some metal
and yet the unit was dropped and it just
totally broke apart because of a sharp
interior edge there
also when you pick up
when you're picking plastics for your housings
you have to be aware of
the environment that plastics going to be in
plastics are sensitive to temperature they
you know they soften
so if you
think that your usage environment may see 80 degrees c
you're okay with abs if you go above 80 degrees c
you're going to have to take a higher temperature
plastic possibly a polycarbonate
yes abs is cheaper than polycarbonate
but if you're going to be
of a death higher temperature
you're going to have to go with a
higher temperature plastic
you also have to be aware that
plastics do not stand with stand uv
that well
you'll have to make sure that
there's uv stabilizers added to the plastic
so that it can be
exposed to the uv and doesn't end up
discoloring or getting surface cracks on it
and then there's this also there's a phenomenon called
environmental stress cracking
which is a combination of
residual stress in the plastic
and a surface
interaction with any type of liquid echoic
this is usually most primarily seen in polycarbonate
it's also it hasn't seen in abs
you know it's more significant of a concern
you're an industrial application
or maybe an outdoor application
I've seen bosses crack
because bosses inherently have a residual stress
because you're putting a thread forming screw in it
that causes the plastic be under a state of stress
it gets a surface contaminant on it
and that is enough to cause it just
to the crack
so then that's just some of the concerns of plastics
so if you selected metal
it's probably because you needed something durable
you may have had to
have some kind of water resistance
or maybe waterproof it
so you're going to have to
most likely you'll be doing some sort of casketing
this is a case of using a flat gasket
you can also use o rings or form in place gaskets
with flat gaskets this happened to be
a metal enclosure that had an lcd screen
which is very common
it was a textured gasket
it passed all its ip 54 braidings yet
because the environment was actually a salt sanding
water that was getting on it
the gasket failed
just due to a phenomenon called
salt jacking is where the salt
where your liquid dries out at least
salt crystals with salt crystals expand
and it creates a path for the liquid to
increase into the enclosure
so just be aware of
what your actual environment is going to be
another concern would be
if you have a metal housing you're going to
probably industrial
probably got a lot of heat
and that's why you pick metal
so you're going to be trying to get that heat
out of the box
you're going to have some choices
with how you get that heat out
one very common choice is the silicon gap pads
just be careful with them
if you over compress them
and you put them in a sealed environment
with a lot of heat
they will outcast and that outcasting
if they can't get away from
the pad will
attack the pad itself
and it's got reversion
the oil it breaks the pad down
and silicon oil is released that silicon oil
loves to spread over everything
leaks through
readily leaks through any type of seal that you have
and makes a nice
early sheen all over your product
you also want to be careful that
if there's any optics inside the box
that you don't use a silicone
thermal interface pad
you can avoid this by using the cast in place
silicon
of
thermal interface material
there's also non silicon based thermal pads
so the final
of topic will touch on it as far as metal housings go
our constraint pcbs
usually occurs
you get this nice
milled housing because you want it nice and rugged
you want to get as much
thermal interface between the housing and the board
so you stick a bunch of bolts through it or screws
you've now made it such that the board
cannot expand and contract because
there's a ct mismatch between aluminum
and pcb
the board is going to want to expand
and contract at a different rate than the housing
it cannot do that
you become
to become what we call it over constrained pcb
it causes localized buckling under components
especially around mounting holes
causes the sauder joints to fail
ways to mitigate this
is
don't overdo the connector don't overdo your fasteners
and if you have a lot of fasteners
make sure your tolerances are such that
the board can
float around those mounting holes a little bit
you don't want them so tight
you don't want it where
you know you're forcing a screw in and it's right up
edge to edge against the hole
you gotta have some float
shoulder bolts or slotted holes work great
even just a slightly larger hole with a
dual washer sam works well also
you gotta let that board be able to
release some of the stress on it
now we'll just talk about some guaranteeing reliability
so how do you design your system
you design it to have a test designed for reliability
historically a lot of
uh dead system designers
have not performed any testing
and when they do perform a test
it's because of the steps for the customer
by the customer
you know sometimes cause customer will say hey
I needed to run at 80 degrees c
and minus 40 degrees c
can you guarantee that
so your electrical engineer
will put that lord in a thermal chamber
said the temperature you know
at those two extremes and make sure everything wrongs
and if it passes great
however that's not really going
yeah that tells you electrically is going to run
it doesn't tell you anything
about how reliable your product is going to be out
of the field
you know not every failure mode can be tested for
and if you're already if you are seeing failures
you know then it's too late
there's just so many modes of
electronic system can fail
between the solder fatigue
board crack
capacitor cracking electrolytic caps failing
there you can't test for all of it
so what we recommend
you design for reliability
based on a few rules of thumb
and a physics of failure to identify the wear out risks
a couple rules of thumb
just a few of them
constant temperature
if you're not
going above 40
a cost temperature is not a issue
if you are going above 40
yes you set to start worrying about
being at the cost temperature
for example 85 degrees c 2000 electrolytic cap
it's running at 85 degrees c
it's not gonna last five years
there's also an issue with solder joints
if your solder joints are running at 75 to 85 degrees c
what happens is
they form the inner metallic starts to grow
and the joint becomes very brittle
they can now
be more susceptible to shock and vibe damage
for temperature cycling
if you're in a low power outdoor environment
not much of an issue
your typical environmental swing
throughout the day is about 25 degrees c
that is sufficiently a low where you shouldn't
you wouldn't have to really worry about
played it through whole
fatigue or sonic electricity
it becomes more of a concern when you start stacking up
different temperatures on you on it
so you have your
if you have thermal loading
now your deltas can see 40 degrees c
okay if the device now has to go through power cycles
that becomes another issue
an automobile under the hood of an automobile
as a person turns the car on a few times a day
it's sitting out in the sun
that's a very harsh environment you
now start having to start worrying about
your solder fatigue your plated through hole cracking
vibration robot
design your board
to be about two x times greater than the highest
energy peaks in the vibration spectrum that you think
the device will say
a good rule of thumb
is your natural frequency for your board
should be around above 250 hertz
if you're around 250 hertz
chances are most things in the field that you're
about to see or your board will say
won't meet that
so you use those rules of thumb to identify
the potential risks
then but
and you really only want those to apply to
components that could wear out
then you would like
then your other approach is
use physics a paylor to calculate lifetime or parts
that are also quite wear out so
you know this tells you what is your actual risk
so physics failure you know
for solder fatigue physics failure for
played it through a whole you know cracking
that type of thing
if you have for example
if you have a very harsh temperature environment
you may have to
mitigate that somehow you may have to corner stake
you may have to underfur your bag
you know that type of thing
so here's a list of what typically wear out electronics
beside from your solder fatigue
and bending these are other things that
can go wrong
ceramic patcher have
an oxygen vacancy migration issue that they can have
you got tin whisker formation
you know anything electromechanical relays
you got to be careful
silver based plated boards components
you know
sulfur environments they're very susceptible too
so for an example on where out of a ceramic caps
this is more
it's more applicable to
your small caps that have a very large for their size
a relatively large capacitance value
and as you can see as the temperature goes up
their useful lifetime is severely affected
and we talked outside I mentioned solder joints already
the reason solder joints are now more
in the forefront as far as
failure issues is because
the industry has moved away
well hasn't moved totally weighed
but people want to move away from
your allowing leaded devices
and this is primarily due to cost
you get rid of that extra
piece of metal
and you have a cheaper part
unfortunately that going is a
compliance act
it adds flexibility to the part
it takes in some of the
c mismatching apart in the board
and therefore you have a longer life
so
as you move away from those lead
the leaded package
and you go to bags and then you go to the fun
and then you go to the even smaller csp
which where the dye is almost as big as the park
your cute mismatch between the part and the board
is all taken in by the solder
there's nothing
nothing decoupling that motion
or that straight distress on each other
and that's why the life of these guys
are a lot less
so you're typically
in this cycle failure from minus 40 to 125
a quad flat pack goldwing
leading quad flat pack
can survive 10,000 cycles
and then you go to the lower end of the extreme
your flip chip cups less than thousand cycles so
you know penic order magnitude change
based on just
the structure of the component
so it figures some of the all the
myriad equations that are
used to do these physics of failures
you know
however if you can get a graph some understanding it
just put you a leg up over your competitors
you know there are some
physics behind what you're saying on your product
so if you can do a plated through hole
cycles to failure analysis
you know
that's just one extra thing that sets you apart from
your competition
so in conclusion
stay agile
yes you can mitigate your risk
but you shouldn't be so
wrapped around
it that it impedes the product development
you gotta just work with it
you mitigate the wrist
you say you show some background behind what you've
been designing
you show that you've done the research where
you can say hey
we study this package this package can survive
you know 110 000 cycles of this thermal profile
that's just that much
better for the gives a level comfort to your customer
improve your processes and tools
add some of those rules of thumb
you know if
add the rules of thumb
based on you know maybe your capacitor sizing
or the thermal load
I think doctor helmet talk about thermal
you know sizing
it helps
and that wraps it up
questions
all right thank you michael
I appreciate another good presentation there
just to
kind of dive into questions here looks like we have one
and the question is is there a life model
to account for high capacitance capacitors
that accounts for the use
of very thin dielectric layers
when you say thin dielectric layers
you mean internal to the capacitor
that what we mean
guess what
I am not aware of one
I can talk to one of our capacitor experts
and get an answer for that at a later time
yeah I'm not aware of one so yeah
that would be something I'd have to talk to
talk to one of the pastor experts here
yeah and the comment back was high
capacitance is obtained by using very
thin dielectric layers
that was from another one of our
webinar attendees
oh okay
no they're just looking at it as a whole these
these charts are just based on the data they've gotten
they're not doing a physics of failure
on this structure of the pastor
all right doesn't look like we
doesn't look like we have any other questions
at this point in time
so if anybody does have some questions
we'll keep the questions
box open for you
michael if you go back to slide 29
I just want to go through
who they can contact
so if you have any additional questions
my information and michael's information are on screen
now feel free to write it down
and shoot us an email or give us a call
if you have any more technical questions
michael is going to be your guy
and then if you want the copy of this webinar
feel free to email me
and we can send that out to you right away
if not it'll be up on dfr solutions
com relatively soon
the micro if you could go to the next slide please
and I just wanted to bring this up
as it is coming up fairly soon
we're having our design for reliability conference
the sheriff inner harbor hotel
and baltimore Maryland
you can sign up or if you're interested in signing up
just please go to dfr solutions
com it will be the first link you can click on
and you're more than welcome to sign up for that
and come out and see us
if you have the time on March 20th
well if you're sure a lot customer
we're also going to be running some sherlock
trainings as well
and that information is on the website
so just
wanted to bring that up for everybody on the line
if you're interested
and find in the area during that time
so with that I'm not seeing any additional questions
so we're going to go ahead and close out the webinar
thank you once again michael and
to all have a great day