hi, I need to generate thermal relief with two spokes instead of four.
Is there a settings for this?
1 Like
Unfortunately no, you can only control the width of the thermal and the gap between pad and fill. To do what you want, edit the pad and in the tab “Local Clearance and and Settings” select Pad Connetion->None. When you do a fill, it will not connect to that pad. You then use 2 tracks to connect the pad to the fill. You need to be very careful though since the DRC will not catch many of the mistakes that can happen in this case; for example if you have fills on 2 layers and forgot to put tracks between the pad and one of the layers.
2 Likes
thank you, I will try with connection none and two traces.
I had 6 GND planes (on a 14 layers PCB) for shielding and matched impedances.
Using 4 spokes it is impossible to get a good soldering
RFE: KiCAD should have two spokes automatic feature.
Some other suggestions on how to solve the soldering trouble?
what is the way to ask for this RFE?
related discussion:
https://lists.launchpad.net/kicad-developers/msg06584.html
Why? Adjusting the width of four spokes is usually adequate in most cases.
Is this through hole, SMD? How are you soldering, by hand, wave, reflow?
Depending on your method of soldering you would generally preheat the board.
as sayd, with the current four spokes it is impossible to get a good wetting of the pins.
those are THT 2 mm hard metric connectors (not pressfit), soldered by hand.
We preheat the PCB at 90° and keep temperature (closed loop check) while soldering with an oven below the PCB. Iron is at 330°.
Neverthenless it is impossible to get a good wetting of hundreds of pins.
If that’s the case using two spokes will probably not improve things much.
You’ll need to reduce the thermal mass in the area of these pins. Have you considered using a hatched plane instead of solid?
our customer forbid use of automatic soldering
this will degrade the electrical performance, so we want to avoid or use as last resource
in aerospace it is normal hand soldering
I find it hard to believe that you are working with circuitry where this would be true and yet you don’t have the means to assemble these boards properly.
Preheating to 90° is not likely going to help much and maintaining a higher temperature for as long as it would take to hand solder 100’s of pins is not feasible either.
I think having the proper soldering equipment and inspection equipment is more “normal” when it comes to assembling PCBs.
Anyway, if you, or your customer, insists on this approach you need to reduce the thermal mass in the area of these pins, perhaps just on some layers but on as many as possible. Just changing the spokes is not likely to help.
the prototype is already tested, but the wetting of these soldered connector isn’t acceptable by the customer. So we are looking for a way to improve soldering without degrading EMC performances.
Why you say two spokes doesn’t improve the wetting?
What about higher iron temperature? I presume you have already tried…
Lead free soldering wants around 400°C
we can’t use lead free alloy, see https://en.wikipedia.org/wiki/Whisker_(metallurgy)
These connectors support as max 350°. Surely next tests will be performed at this limit.
In your case there are six internal ground planes. FR4 is a poor thermal conductor so it’s hard to preheat all these internal planes, especially at 90°.
Increasing the clearance around the pads (longer spokes) would help as it also reduces the thermal mass in the area of the pin but 2mm pitch doesn’t give you much room for that especially when KiCAD likes to orientate it’s spokes at 45°. If having only two spokes would solve your problem then having four narrower spokes would as well.
3 Likes
You don’t use conformal coatings?
yes it is mandatory, but trials shown that with coating alone, whiskering is not avoided in space env (vacuum, radiations and MIL thermal cycles -55 to 125°C), expecially long lasting missions like deep space and geostationery
we use Polyimmide (Kapton like) only, as FR4 bad performance. Anyway PI has low thermal conduction too.
we are at those spokes size:
width: 0.15 mm
lenght: 0.25 mm
that are about the manufacturing limits of space qualified PCB manufacturers and space between pins.
This is why I’m undertaking the way of two spokes, the last chance.
I saw in another thread that rotating the pad by 45° KiCad made a cross like TR
hope
compactpci report, 8-3-07.pdf (668.8 KB)
we use the Hypertronics connectors spoken in the attachment.
As seens there, many space companies hit the wetting troubles.
That’s possible, I’ve never tried that.
If you rotated the pad and increased the clearance you should end up with only one or two spokes anyway.
As cited in that report the thermal mass of those connectors combined with the thermal mass of the PCB is problematic. I’m sure it is even more so with a 14 layer board and planes on 6 of those layers. You need to reduce the thermal mass in the area of these pins as much as possible, and two spokes are just not that significant. And perhaps adjust your soldering methods.
You never mentioned these boards were for a space application. Another reason why you should be oven soldering these boards.Soldering technique can also influence the formation of whiskers. You also need to avoid using components with tin plated leads.