flexible ribbon "PCB" to regular PCB

[Winfield Hill]

Looking for good ways to connect / solder a flexible ribbon PCB to a regular
PCB, without using a connector. We need to be able to pull hard on the link,
without the flexible ribbon coming out. Maybe using Molex Premo-Flex, etc., to
avoid having to fab the flexible ribbon? We only need four wires, for an I2C
connection.


--
Thanks,
- Win

 

[TTman]

On 01/05/2019 12:56, Winfield Hill wrote:

Looking for good ways to connect / solder a flexible ribbon PCB to a regular
PCB, without using a connector. We need to be able to pull hard on the link,
without the flexible ribbon coming out. Maybe using Molex Premo-Flex, etc., to
avoid having to fab the flexible ribbon? We only need four wires, for an I2C
connection.

I've seen them soldered directly to a PCB- it was very unreliable so
don't go that route (on an LCD to PCB backlight)

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[Winfield Hill]

TTman wrote...

On 01/05/2019 12:56, Winfield Hill wrote:
Looking for good ways to connect / solder a flexible ribbon PCB to a
regular PCB, without using a connector. We need to be able to pull
hard on the link, without the flexible ribbon coming out. Maybe using
Molex Premo-Flex, etc., to avoid having to fab the flexible ribbon?
We only need four wires, for an I2C connection.

I've seen them soldered directly to a PCB- it was very
unreliable so don't go that route (on an LCD to PCB backlight).

OK, good advice. I can use the recommended connector, and after
mating the ribbon, seal the entrance and cover it all with epoxy.
I see 1.25mm six-wire is only 9 mm wide, but I assume it's strong.


--
Thanks,
- Win

 

[Tom Del Rosso]

Winfield Hill wrote:

TTman wrote...

On 01/05/2019 12:56, Winfield Hill wrote:
Looking for good ways to connect / solder a flexible ribbon PCB to a
regular PCB, without using a connector. We need to be able to pull
hard on the link, without the flexible ribbon coming out. Maybe
using Molex Premo-Flex, etc., to avoid having to fab the flexible
ribbon? We only need four wires, for an I2C connection.

I've seen them soldered directly to a PCB- it was very
unreliable so don't go that route (on an LCD to PCB backlight).

OK, good advice. I can use the recommended connector, and after
mating the ribbon, seal the entrance and cover it all with epoxy.
I see 1.25mm six-wire is only 9 mm wide, but I assume it's strong.

Pass it through a slot in the board first to give it more strength.
Epoxy it there too.

 

[Winfield Hill]

Tom Del Rosso wrote...

Winfield Hill wrote:
TTman wrote...

On 01/05/2019 12:56, Winfield Hill wrote:
Looking for good ways to connect / solder a flexible ribbon PCB to a
regular PCB, without using a connector. We need to be able to pull
hard on the link, without the flexible ribbon coming out. Maybe
using Molex Premo-Flex, etc., to avoid having to fab the flexible
ribbon? We only need four wires, for an I2C connection.

I've seen them soldered directly to a PCB- it was very
unreliable so don't go that route (on an LCD to PCB backlight).

OK, good advice. I can use the recommended connector, and after
mating the ribbon, seal the entrance and cover it all with epoxy.
I see 1.25mm six-wire is only 9 mm wide, but I assume it's strong.

Pass it through a slot in the board first to give it
more strength. Epoxy it there too.

Awesome idea!


--
Thanks,
- Win

 

On Wednesday, 1 May 2019 12:56:54 UTC+1, Winfield Hill wrote:

Looking for good ways to connect / solder a flexible ribbon PCB to a regular
PCB, without using a connector. We need to be able to pull hard on the link,
without the flexible ribbon coming out.

then you're out of luck, solder isn't that robust.
You can feed it through 2 slots to improve things, but it still won't be long term tuggable. Maybe 8 slots

NT

Maybe using Molex Premo-Flex, etc., to
avoid having to fab the flexible ribbon? We only need four wires, for an I2C
connection.

 

[TTman]

On 01/05/2019 15:36, Winfield Hill wrote:

Tom Del Rosso wrote...

Winfield Hill wrote:
TTman wrote...

On 01/05/2019 12:56, Winfield Hill wrote:
Looking for good ways to connect / solder a flexible ribbon PCB to a
regular PCB, without using a connector. We need to be able to pull
hard on the link, without the flexible ribbon coming out. Maybe
using Molex Premo-Flex, etc., to avoid having to fab the flexible
ribbon? We only need four wires, for an I2C connection.

I've seen them soldered directly to a PCB- it was very
unreliable so don't go that route (on an LCD to PCB backlight).

OK, good advice. I can use the recommended connector, and after
mating the ribbon, seal the entrance and cover it all with epoxy.
I see 1.25mm six-wire is only 9 mm wide, but I assume it's strong.

Pass it through a slot in the board first to give it
more strength. Epoxy it there too.

Awesome idea!


I'd prefer to use clear silicone- a bit of flexibility/resilience

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[Winfield Hill]

Tim Williams wrote...

Winfield Hill wrote,

Yes, but it peels off easily. Hmm, hot glue is slightly
flexible, and doesn't peel quite so readily.

Depends on type, of course. I would also recommend 3M VHB tape.
Maybe that, inbetween two slots, with the connector on the exit
side, tape on the opposite side and the cable routed between
all three in a zig-zag fashion, would be best.

God ideas, thanks!

Incidentally, mind EMI. I2C is not "inter-printed circuit"
for a reason. Even with a ground plane on that cable, don't
expect much performance!

We'll be using a slow data rate. With a choice of pin
order, how would you arrange +3.3, SDA, SCL and GND?


--
Thanks,
- Win

 

[Tim Williams]

"Winfield Hill" <hill@rowland.harvard.edu> wrote in message
news:qacjqt0tfk@drn.newsguy.com...

Yes, but it peels off easily. Hmm, hot glue is slightly
flexible, and doesn't peel quite so readily.

Depends on type, of course. I would also recommend 3M VHB tape. Maybe
that, inbetween two slots, with the connector on the exit side, tape on the
opposite side and the cable routed between all three in a zig-zag fashiion,
would be best.

Incidentally, mind EMI. I2C is not "inter-printed circuit" for a reason.
Even with a ground plane on that cable, don't expect much performance!

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

 

[Winfield Hill]

TTman wrote...

On 01/05/2019 15:36, Winfield Hill wrote:
Tom Del Rosso wrote...

Winfield Hill wrote:
TTman wrote...

On 01/05/2019 12:56, Winfield Hill wrote:
Looking for good ways to connect / solder a flexible ribbon PCB to a
regular PCB, without using a connector. We need to be able to pull
hard on the link, without the flexible ribbon coming out. Maybe
using Molex Premo-Flex, etc., to avoid having to fab the flexible
ribbon? We only need four wires, for an I2C connection.

I've seen them soldered directly to a PCB- it was very
unreliable so don't go that route (on an LCD to PCB backlight).

OK, good advice. I can use the recommended connector, and after
mating the ribbon, seal the entrance and cover it all with epoxy.
I see 1.25mm six-wire is only 9 mm wide, but I assume it's strong.

Pass it through a slot in the board first to give it
more strength. Epoxy it there too.

Awesome idea!

I'd prefer to use clear silicone- a bit of flexibility/resilience

Yes, but it peels off easily. Hmm, hot glue is slightly
flexible, and doesn't peel quite so readily.


--
Thanks,
- Win

 

[Tim Williams]

"Winfield Hill" <hill@rowland.harvard.edu> wrote in message
news:qaclst0104r@drn.newsguy.com...

We'll be using a slow data rate. With a choice of pin
order, how would you arrange +3.3, SDA, SCL and GND?

+3.3, SDA, GND, SCL, GND. Or actually, putting 3.3 in the middle and GNDs
at the ends may be better for hot-plugging or cable-wearing purposes, but
not relevant electromagnetically (as long as there's a bypass cap from 3.3
to GND at each end, which there usually is; for the same reason, always
connect all GNDs and supplies at the connector, whether you need the current
capacity or not).

I forget if 5-pin cables or connectors are common. Maybe you're stuck with
4 for space, or 6 for availability?

Low data rates may not be enough, because of noise generating false clocks.
I2C is generally tolerant of fast noise, but a cable exposes a much broader
bandwidth than PCB traces do; it can pay to add ferrite beads (for damping
and filtering) and small caps (as many pF as you can afford, usually
100-470) at both ends of the cable. Uh, beads facing the cable, that is.

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

 

[Tim Williams]

"Tom Del Rosso" <fizzbintuesday@that-google-mail-domain.com> wrote in
message news:qacn7r$kvg$1@dont-email.me...

Low data rates may not be enough, because of noise generating false
clocks. I2C is generally tolerant of fast noise, but a cable exposes
a much broader bandwidth than PCB traces do; it can pay to add
ferrite beads (for damping and filtering) and small caps (as many pF
as you can afford, usually 100-470) at both ends of the cable. Uh,
beads facing the cable, that is.

Beads on a kapton cable? (Or "flexible PCB" as it was described.)

Ah, on the signals that is.

You would be able to put a clamp bead over the cable though, which is also a
good idea if you find noise to be a problem.

Did basically that, five years ago, on a device with a mainboard and a HID
board, connected by a 6" ribbon cable carrying I2C. It failed radiated
susceptibility at ~200MHz (basically the resonant mode of the two boards
joined by the cable). A clamp bead fixed it (damping the resonant mode -->
less V dropped across the cable at F_res).

That same project, had a number of issues that we strongly recommended
against, but which the customer demanded regardless. The elephant in the
box was they wanted USB over unshielded cables... Apparently it managed to
pass radiated, but EFT knocked it out. We were forced to use shielded
enclosures, cables and connectors (instead of nice cheap plastic automotive
connectors), nearly doubling the product cost...

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

 

[Tom Del Rosso]

Winfield Hill wrote:

Tom Del Rosso wrote...

Winfield Hill wrote:
TTman wrote...

On 01/05/2019 12:56, Winfield Hill wrote:
Looking for good ways to connect / solder a flexible ribbon PCB
to a regular PCB, without using a connector. We need to be able
to pull hard on the link, without the flexible ribbon coming out.
Maybe using Molex Premo-Flex, etc., to avoid having to fab the
flexible ribbon? We only need four wires, for an I2C connection.

I've seen them soldered directly to a PCB- it was very
unreliable so don't go that route (on an LCD to PCB backlight).

OK, good advice. I can use the recommended connector, and after
mating the ribbon, seal the entrance and cover it all with epoxy.
I see 1.25mm six-wire is only 9 mm wide, but I assume it's strong.

Pass it through a slot in the board first to give it
more strength. Epoxy it there too.

Awesome idea!

Or make it wide enough for a hole or 2 and screw it down. Glue below
and washer on top.

Or if PCB slots or washers are too sharp on the edges, and might cause
it to break, a few large guage wires with insulation, can be mounted
like jumpers closely in parallel. Then you can zigzag around them, and
glue. That should give it the least stress.

 

[Tom Del Rosso]

Tim Williams wrote:

"Winfield Hill" <hill@rowland.harvard.edu> wrote in message
news:qaclst0104r@drn.newsguy.com...

We'll be using a slow data rate. With a choice of pin
order, how would you arrange +3.3, SDA, SCL and GND?


+3.3, SDA, GND, SCL, GND. Or actually, putting 3.3 in the middle and
GNDs at the ends may be better for hot-plugging or cable-wearing
purposes, but not relevant electromagnetically (as long as there's a
bypass cap from 3.3 to GND at each end, which there usually is; for
the same reason, always connect all GNDs and supplies at the
connector, whether you need the current capacity or not).

I forget if 5-pin cables or connectors are common. Maybe you're
stuck with 4 for space, or 6 for availability?

Low data rates may not be enough, because of noise generating false
clocks. I2C is generally tolerant of fast noise, but a cable exposes
a much broader bandwidth than PCB traces do; it can pay to add
ferrite beads (for damping and filtering) and small caps (as many pF
as you can afford, usually 100-470) at both ends of the cable. Uh,
beads facing the cable, that is.

Beads on a kapton cable? (Or "flexible PCB" as it was described.)

 

[whit3rd]

On Wednesday, May 1, 2019 at 4:56:54 AM UTC-7, Winfield Hill wrote:

Looking for good ways to connect / solder a flexible ribbon PCB to a regular
PCB, without using a connector. We need to be able to pull hard on the link,
without the flexible ribbon coming out.

One possibility (that i've never seen used) is to put holes in the
flex, to engage pins, for mechanical positioning, then apply a
clamp over a flex/ zebra-stripe/PCB sandwich. This isn't much of an improvement
over 'using a connector', though, it has loose parts to be
assembled. With the right plastics manufacturer, it'd be two; zebra
elastomer and snap-over plate (holes in PCB and flex engage the plate's
plastic snaps).

 

[Hul Tytus]

Win - ribon cable, ala Belden, etc, is a "golden oldie" for such
applications. Typically, though, a ground lead for each signal lead is
required.

Hul

Winfield Hill <hill@rowland.harvard.edu> wrote:

Looking for good ways to connect / solder a flexible ribbon PCB to a regular
PCB, without using a connector. We need to be able to pull hard on the link,
without the flexible ribbon coming out. Maybe using Molex Premo-Flex, etc., to
avoid having to fab the flexible ribbon? We only need four wires, for an I2C
connection.

--
Thanks,
- Win

 

[Lasse Langwadt Christense]

torsdag den 2. maj 2019 kl. 00.06.01 UTC+2 skrev Winfield Hill:

Hul Tytus wrote...

Win - ribbon cable, ala Belden, etc, is a "golden
oldie" for such applications. Typically, though,
a ground lead for each signal lead is required.

Thanks, but this time we need the super-thin aspect.
It sneaks between two "supers" = bee-hive sections.
We only need four I2C wires, but the smallest
stocked Molex 1.25mm Premo-Flex has six.

does it have to be molex and 1.25?

https://uk.farnell.com/pro-power/pp001497/ffc-jumper-cable-1-25mm-4core/dp/2776622

or

https://www.ebay.com/itm/253348078506

 

[Winfield Hill]

Hul Tytus wrote...

Win - ribbon cable, ala Belden, etc, is a "golden
oldie" for such applications. Typically, though,
a ground lead for each signal lead is required.

Thanks, but this time we need the super-thin aspect.
It sneaks between two "supers" = bee-hive sections.
We only need four I2C wires, but the smallest
stocked Molex 1.25mm Premo-Flex has six.


--
Thanks,
- Win

 

[Winfield Hill]

Lasse Langwadt Christensen wrote...

torsdag den 2. maj 2019 kl. 00.06.01 UTC+2 skrev Winfield Hill:
Hul Tytus wrote...

Win - ribbon cable, ala Belden, etc, is a "golden
oldie" for such applications. Typically, though,
a ground lead for each signal lead is required.

Thanks, but this time we need the super-thin aspect.
It sneaks between two "supers" = bee-hive sections.
We only need four I2C wires, but the smallest
stocked Molex 1.25mm Premo-Flex has six.

does it have to be molex and 1.25?

https://uk.farnell.com/pro-power/pp001497/ffc-jumper-cable-1-25mm-4core/dp/2776622

or

https://www.ebay.com/itm/253348078506

No, it could be either of those, but then I'd have to
be confidant of the mating connector. We do need super
thin. Haha, I'm not really sure of the Molex Premo-Flex
thickness spec. I can see it's really thin.


--
Thanks,
- Win

 

On Wednesday, May 1, 2019 at 7:56:54 AM UTC-4, Winfield Hill wrote:

Looking for good ways to connect / solder a flexible ribbon PCB to a regular
PCB, without using a connector. We need to be able to pull hard on the link,
without the flexible ribbon coming out. Maybe using Molex Premo-Flex, etc., to
avoid having to fab the flexible ribbon? We only need four wires, for an I2C
connection.

They make a flat cable termination that is intended for soldering to a PCB. It has pins for through hold mounting, very secure. I want to say the individual pins in the body crimp to the flex, but I'm not certain of that. It might need to be made part of the cable. Do you not see anything like this in premade flex catalogs?

--

Rick C.

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