mSATA PCIe connector

[Ricky C]

On Saturday, April 4, 2020 at 1:02:33 PM UTC-4, Winfield Hill wrote:

Randy Day wrote...

Even with alignment pins/tabs, I stand by my previous
statement: avoid SMT connectors if you can.

The issue is less of concern if the connector has
many pins, providing strength, such as the 52-pin
mSATA connector. And its users are (carefully)
installing and fastening in place a fixed PCB,
rather than a connector with an attached cable.

I wouldn't play that card. I think the attached cable case would be less stress with a much shorter lever arm. I've seen 44 pin connectors ripped off a main board from multiple attach cycles. Eventually the solder just gets tired and cracks from the repeated stress. It depends on the number of cycles more I think. 10 or maybe 100 is ok. 1000 is clearly asking for trouble.

--

Rick C.

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[Ricky C]

On Saturday, April 4, 2020 at 11:31:37 AM UTC-4, Randy Day wrote:

In article <a56eba46-3754-4ec4-92c3-5ac40472eb82@googlegroups.com>,
gnuarm.deletethisbit@gmail.com says...

[snip]

Just my opinion, take it for what it's worth...

That is certainly true of connectors without alignment pins.
The alignment pins take strain off the solder joints. I use a surface
mount connector on my board with mating surface mount parts on the
motherboard (which I didn't design). The motherboard parts don't have
alignment pins and get used over and over with no failures so far, so
I'm expecting my boards to do just fine. So far, no problems in
around 10,000 units, 20,000 connectors. Can't be all bad.

It will be interesting to see how they hold up long-term.
Your users must be less ham-fisted than ours.

This product is in it's twelfth year, so long-term is here, now. The boards are integrated into chassis which is where they sheered off the tall caps, so no, I don't think they are any less ham-fisted.

If the alignment pins press-fit into the alignment holes,
yes, they can take up much of the strain. If it's the
common small-pin-in-a-larger-PCB-hole alignment, not so
much. If the alignment pins are soldered through-hole,
why not all the pins?

The alignment pins are not soldered. But the hole to pin clearance is not large and the surface mount pins are long enough to yield a bit, so the alignment pins take the brunt of any sideways stress.

The mating connector on the test fixture does have soldered pins. That connector has seen many thousands of uses.

We tried an SMT USB connector with through-hole solder
tabs to hold it to the board; our crews still found ways
to break them loose. I've got name-brand laptops on the
dead equipment shelf with trashed charge jacks (SMT)
that ripped loose over time.

I have trouble with the power cords on laptops. The connectors protrude far too much and act as a lever arm allowing damage to the mating connector when the laptop is actually used in the lap or in bed. The connector is not SM rather mounted to the case, but the connector itself breaks so that the mating connector no longer is held securely. When I fix this one I think I'm going to run a wire out the back and let it be a captive cable with the connector on the end.

Even with alignment pins/tabs, I stand by my previous
statement: avoid SMT connectors if you can.

Sure, but the "if you can" is a big issue. There was literally no way I could have built my current board if the connector used both sides of the PWB.. It was barely possible with SMT.

--

Rick C.

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[Randy Day]

In article <r6aeiq01c02@drn.newsguy.com>, winfieldhill@yahoo.com says...

Randy Day wrote...

Even with alignment pins/tabs, I stand by my previous
statement: avoid SMT connectors if you can.

The issue is less of concern if the connector has
many pins, providing strength, such as the 52-pin
mSATA connector. And its users are (carefully)
installing and fastening in place a fixed PCB,
rather than a connector with an attached cable.

Oh, how I long to have 'careful' users!

We have one device with a Hirose 40-pin mezzanine
connector we're just now building daughterboards for.
I suspect you're right, but I still wonder about
lateral movement as the dboard slips and sticks
under mounting bolts, and vibrates on standoffs.

We have another unit with a number of 2-pin SMT
headers sandwiched between main- and daughterboard.
Even bolted together at all corners, those 2-pin
headers are the most common failure point(s) as
vibration & shock pull and tear at the pads.

If we're lucky, the solder joint gives way before
the traces do...

RD

 

[Ricky C]

On Saturday, April 4, 2020 at 3:01:00 PM UTC-4, Randy Day wrote:

In article <r6aeiq01c02@drn.newsguy.com>, winfieldhill@yahoo.com says...

Randy Day wrote...

Even with alignment pins/tabs, I stand by my previous
statement: avoid SMT connectors if you can.

The issue is less of concern if the connector has
many pins, providing strength, such as the 52-pin
mSATA connector. And its users are (carefully)
installing and fastening in place a fixed PCB,
rather than a connector with an attached cable.

Oh, how I long to have 'careful' users!

We have one device with a Hirose 40-pin mezzanine
connector we're just now building daughterboards for.
I suspect you're right, but I still wonder about
lateral movement as the dboard slips and sticks
under mounting bolts, and vibrates on standoffs.

We have another unit with a number of 2-pin SMT
headers sandwiched between main- and daughterboard.
Even bolted together at all corners, those 2-pin
headers are the most common failure point(s) as
vibration & shock pull and tear at the pads.

If we're lucky, the solder joint gives way before
the traces do...

What sort of environment are your boards used in if they are getting vibrated broken with four mounting screws?

I find it hard to picture traces being lifted in this situation.

--

Rick C.

--+ Get 1,000 miles of free Supercharging
--+ Tesla referral code - https://ts.la/richard11209

 

[whit3rd]

On Saturday, April 4, 2020 at 8:31:37 AM UTC-7, Randy Day wrote:

In article <a56eba46-3754-4ec4-92c3-5ac40472eb82@googlegroups.com>,
gnuarm.deletethisbit@gmail.com says...

The alignment pins take strain off the solder joints.

It will be interesting to see how they hold up long-term.
Your users must be less ham-fisted than ours.

If the alignment pins press-fit into the alignment holes,
yes, they can take up much of the strain

Another kind of surface-mount connector is the zebra-strip; if you
can clean the contact area, and if the strips are replaceable, expendable
units, one would expect good reliability in high-density connections.
It's certainly inexpensive in the parts-count sense.

 

[Randy Day]

In article <75225f10-e0b1-442c-92db-1ce8b27e82d8@googlegroups.com>,
whit3rd@gmail.com says...

[snip]

Another kind of surface-mount connector is the zebra-strip; if you
can clean the contact area, and if the strips are replaceable, expendable
units, one would expect good reliability in high-density connections.
It's certainly inexpensive in the parts-count sense.

I've seen them used in cheap chinese multimeters.
They seem to work well enough. I could see them
being a bit more tolerant of board shifting than
a hard plastic interconnect.

RD

 

[Randy Day]

In article <aeca6d6f-d736-4274-a52f-cfd9f6ff21bf@googlegroups.com>,
gnuarm.deletethisbit@gmail.com says...

[snip]

If we're lucky, the solder joint gives way before
the traces do...

What sort of environment are your boards used in if they are getting vibrated broken with four mounting screws?

I find it hard to picture traces being lifted in this situation.

Geophysical equipment. Shipped on an aircraft, tossed
in a pickup, washboarded over gravel roads, loaded on
a float plane, dragged through the bush, falls off a
rock face, chewed on by bears, that sort of thing.

Winter/summer, subarctic to desert. And no, I'm not
kidding about the bears...

Crews at the end of a weeks-long survey are not inclined
to be dainty with this stuff, either.

The equipment works very well, but it's a rare project
that comes back without some amount of breakage.

The way I see it, if a damaging force (e.g. bear's
tooth) hits a through-hole connector, the body will
probably break free from the board. If the connector
is SMT, it's taking traces with it...

RD

 

[Ricky C]

On Saturday, April 4, 2020 at 7:57:43 PM UTC-4, Randy Day wrote:

In article <75225f10-e0b1-442c-92db-1ce8b27e82d8@googlegroups.com>,
whit3rd@gmail.com says...

[snip]

Another kind of surface-mount connector is the zebra-strip; if you
can clean the contact area, and if the strips are replaceable, expendable
units, one would expect good reliability in high-density connections.
It's certainly inexpensive in the parts-count sense.

I've seen them used in cheap chinese multimeters.
They seem to work well enough. I could see them
being a bit more tolerant of board shifting than
a hard plastic interconnect.

I like the way you refer to using your equipment as a chew toy for Grizzly bears as "board shifting". That's a bit like referring to using C4 as a "motivational tool".

--

Rick C.

-++ Get 1,000 miles of free Supercharging
-++ Tesla referral code - https://ts.la/richard11209

 

[Ricky C]

On Saturday, April 4, 2020 at 7:51:14 PM UTC-4, Randy Day wrote:

In article <aeca6d6f-d736-4274-a52f-cfd9f6ff21bf@googlegroups.com>,
gnuarm.deletethisbit@gmail.com says...

[snip]

If we're lucky, the solder joint gives way before
the traces do...

What sort of environment are your boards used in if they are getting vibrated broken with four mounting screws?

I find it hard to picture traces being lifted in this situation.

Geophysical equipment. Shipped on an aircraft, tossed
in a pickup, washboarded over gravel roads, loaded on
a float plane, dragged through the bush, falls off a
rock face, chewed on by bears, that sort of thing.

Winter/summer, subarctic to desert. And no, I'm not
kidding about the bears...

Crews at the end of a weeks-long survey are not inclined
to be dainty with this stuff, either.

The equipment works very well, but it's a rare project
that comes back without some amount of breakage.

The way I see it, if a damaging force (e.g. bear's
tooth) hits a through-hole connector, the body will
probably break free from the board. If the connector
is SMT, it's taking traces with it...

Oh, I see, you are playing the Grizzly Ben card. Ok, you win. No surface mount for you... and your bears should see a dentist regularly.

--

Rick C.

-+- Get 1,000 miles of free Supercharging
-+- Tesla referral code - https://ts.la/richard11209