PCB Pins for Blind Plated-Through Holes

[Smoky]

I'm looking to make my first PCB using EasyEDA and it's an adapter board.

I need to use a 4 sided PCB and I was wondering how to have blind PCB pins installed in the botton layer's plated-through holes.

Is it just something that I request afterwards?

The adapter board will be inserted into a socket so would the pins best be a soldered-in type or are solderless press-fit types durable enough for a push/pull environment?

I have read Mill-Max's catalog about proper hole sizes, etc for their pins. Do I need to give JLCPCB the correct part number or do they use generic pins?

Thanks!

[Doctorandus_P]

PCB manufacturers do not use any sort of pins, but they use balls of pure copper, about 50 to 80mm in diameter. Then they put those in an acid bath together with the PCB and use an electrochemical process to dissolve the copper from the balls and deposit it on the PCB.

There are a bunch of youtube videos about PCB manufacturing and you can watch some of them if you want to know more details.

[Smoky]

I just watched a tutorial using EasyEDA and I'm rethinking the whole process of getting what I need done.

A "stacked" PCB may be the better/easier option

[Doctorandus_P]

What is it that you need getting done exactly?
From your first post, I gather you are a beginner in PCB design, and if you tell us more about what you want we can give you a push in the right direction.

In general, 4 layer (not sides) PCB's are more expensive then 2 layer PCB's, and only a part of that cost is the extra layers. It's also more expensive because 2 layer PCB's are typically made on a lower resolution process overall, so you can use smaller track widths, annular rings etc, on 4 layer PCB's.

Also, typically via's are always through the whole PCB and connect to all layers (when there is copper at the location of the via) It is possible to use "blind" or "buried" via's that do not connect on all PCB layers, but those necessitate extra process steps and Will make your PCB more expensive.

I am also curious why you choose EasyEDA. (I am a big KiCad fan myself).

[Smoky]

I want to add PC pins in a 32-dip 400mil arrangement on the bottom layer of the PCB.

I scoured YouTube and watched a video on blind and buried vias.

I'm guessing now that I need to create a 32-DIP 400mil pattern of plated blind vias with the correct diameter/depth, (for example 1.28mm Diameter for Mill-Max 4219 series pins), allowing blind PC pins to be pressed into them.

I'll be using through-vias from the top of the board to the bottom and connecting them to the blind vias with small traces.

It looks like what I need done can now be done with a two sided PCB.

I'm using SMD's parts/pads on the top layer so, of course, no penetration from the PC pins can come through from the bottom.

Does this somewhat describe the proper process?

[Kean]

Blind (& buried) vias are for interconnections between certain layers only in multi-layer PCBs, and are not really usable for mounting connector pins.  Even if you made the via drills big enough and could solder the pins in, they would not have any mechanical strength.

What you probably want is a SMT pin header - e.g. something like Samtec TSM-116-01-L-SV.  There are cheaper versions from other mfgs, and also round pin versions which will work better if being plugged into a DIP socket rather than sockets intended for square pins.

[Smoky]

Mill-Max shows these pins being used in a plate-through hole but I was thinking that they might work in a plated blind via:



That's why I was thinking of using a 4 layer board initially to possibly grab the inner two layer copper pads for added "pull-out" strength

[Kean]

Do you really need blind vias?  Do you actually understand what they are?  As I mentioned, I've never seen blind vias used to solder parts.  And you can't have blind vias with only 2 layers.
Depending on the 4-layer stackup, a blind via from layer 3 to 4 will at most go through half the PCB thickness (i.e. 0.8mm for JLC 7628).  https://jlcpcb.com/help/article/364-multi-layer-pcb-standard-laminated-structures

Can't you just position parts on the top layer between/around the through holes needed for the DIP header?  You can use short pins line those MilMax ones so they don't protrude significantly.

[Smoky]

I seen this cut-away picture described as a blind plated via:



I thought that the square shank of the Mill-Max pin would still grab.

[Smoky]

I just noticed that the title of this thread is wrong. it should read:

 "PCB Pins for Blind Plated Holes"

or

 "Press-Fit Pins for Blind Plated Holes"

...or something like that

[wraper]

Sounds like some really weird and expensive idea. Unless extremely necessary, use TH or SMT terminals. Or use two adapter PCBs stacked which is very common on programming adapters.

[Doctorandus_P]

Mill-Max shows these pins being used in a plate-through hole but I was thinking that they might work in a plated blind via:

No, that is never going to work.
Blind via's only go though one layer of prepreg, which is about 0.2mm thick or thereabouts. It is far to thin to hold such pins in place. All through holes are the only option. In your PCB program, use THT holes such as used for DIP IC's and headers, and do not use vias for this. The diameter for such holes is quite critical, and diameters for via's are less tightly controlled and are often also partly filled with solder mask or other crud.

If you do it "right" you even have to communicate with your PCB manufacturer about this, because of the required tight hole tolerance. It is for example quite common that slightly different drill sizes can be used as substitutes when batches of PCB's are made for different customers, and this may make the holes to big or to narrow for your purpose.

[Kean]

A via is for connecting layers.  Even when it is through all layers, it is different from a plated through hole (PTH) intended for pins/component legs, as it will generally be smaller diameter and can be partially or completely filled (intentionally or not).

Blind vias are from outer layer to one or more inner layers - and can add significant cost due to the extra manufacturing steps involved.  The way they are manufactured will not work for inserting/holding a pin.

I've seen capability specs for blind vias that they should not exceed 300um not sure if that is IPC standard or just recommendation.  There are also specific aspect ratio requirements for them.  JLC don't give much detail that I could find as they didn't use to even offer blind and buried vias at all.  Here is an example from another supplier (just one I found via a quick search)  https://www.multi-circuit-boards.eu/en/pcb-design-aid/drills-throughplating/blind-via-buried-via.html

Of course you can attempt designing a PCB however you want, but I doubt it will work the way you suggest assuming the PCB house will even be willing to make it for you.

[Smoky]

I visited Proto-Advantage.com's website and they sell some nice adapter boards.

Here's a 28-DIP adapter board using round pins that I can use:





Unfortunately, they don't sell any boards with a 32-DIP 400mil footprint. They have 600mil spaced ones though.

I'll send them an e-mail to see if it's possible that they can produce a few

And, maybe, they can shed some light on how they make theirs.

[Doctorandus_P]

From the last picture, it's clear those pins are soldered to the underside of the board, and very likely both the solder and the pins themselves are just flat. But the via's do not go all the way through either, and this is unusual, because blind via's normally only go through a prepreg layer, and not through the core of the PCB. I'm guessing that maybe both buried vias (for the inner core) and blind via's (to an outside layer) are being used.

Very likely they have some kind of mold to keep those pins in place during soldering. For low volume applications a piece of perfboard would do, but for "real" production they probably have something more fancy.

I also guess that neither blind nor buried via's are very expensive, but most of the (usual) costs is just because they are not used very often or in mixed panels for different customers. I also noticed that if you for example buy 1000 PCB from a manufacturer within the EU such as Eurocircuits, then PCB's are also quite cheap. often less than EUR1 a piece.
The board would be easy to design if you use both buried and blind via's. You can try some online calculators to get an idea of the costs at different quantities. DIY soldering is doable if you can find those solder pins. But for a DIY method, it is probably more logical to design 2 PCB's and then glue or solder them together.

[Kean]

Yes, something like Mill-Max 349-10-116-00-560000 SMT pins but lower profile and without the insulation holding them together

https://www.digikey.com/en/products/detail/mill-max-manufacturing-corp/349-10-116-00-560000/3915112

[abeyer]

I visited Proto-Advantage.com's website and they sell some nice adapter boards.

Here's a 28-DIP adapter board using round pins that I can use:

If you're just after an adapter with pins why not lay one out yourself with smt headers? That seems way easier than what you're asking for (though I'm still a little confused as to what you even think you want.)

[Smoky]

I had seen PC boards with pins on the bottom layer but they didn't protrude through the top layer of the board.

I figured that they were pressed into blind holes but now I see that they are surface-mounted pins.

I can't imagine that it would take much effort to snap or pull one off and take the pad and/or trace with it.

I plan to order some boards now with surface-mounted pads at the bottom but I'm going to request if they could drill blind holes in a 32-DIP 400mil pattern through the pad to help with alignment. Some SMT pins have a shoulder but also a little nub that could center in a dimple.

I looked at the Samtec products but the board I plan to make is very narrow and the legs would over-shoot the edge.

All is good now and, yeah, the title of this thread reads wrong.

[thm_w]

The proto advantage board looks like its using one of these mill-max:
https://www.mill-max.com/products/new/tape-reel-packaged-smt-pin
https://www.mill-max.com/products/new/sure-hold-surface-mount-pcb-pins

You could also use normal plated through hole 2-layer PCB, and offset the pins from the SMD package. Then use pins that don't go through all the PCB, as you were thinking of above.

[Smoky]

Proto-Advantage replied saying they'll make the boards

An SOIC-32 to DIP-32 Narrow 0.4” SMT Adapter Compact Series (board width .550").

New part# PA0012C-N4.

They have a great selection of adapter boards and now it'll be even better!