What via filling method is cheapest? Most reliable? - Page 1
Forum section: electronics / general

author: Helix70
author_rank: Unknown
timestamp: February 15, 2017, 06:26:48 am
content: Hi guys,I have a 2 layer PCB that accepts a battery connection and 4 serial data lines. The battery is fine, but the serial data uses gold plated pads mated to via pogo pins. These pads are exposed to the outside world, and there is a plastic housing with an o-ring seal around them. The rest of the parts are on the other side of the PCB, inside the sealed unit. It is IP68 rated.The problem is, running tracks under the o-ring causes leaks. Using standard vias inside the seal area also risks leaking. So I have come up with some options:(Seehttps://www.pcbuniverse.com/pcbu-tech-tips.php?a=5for pictures)Tented vias are not reliable enough, and not an option.1) 4 layer PCB and use blind vias (seehttps://en.wikipedia.org/wiki/Via_(electronics)#/media/File:Via_Types.svg- type 2) from layer 3 to 4, thus maintaining the seal from layer 1-3.2) Mask Plugged vias (filled with solder mask) separate to the pads and dog bone connected3) Via in Pad (Active Pad), like used for BGA4) Vias plated shutWhich style vias/PCB will be cheaper?Which will be most reliable?Which will be easiest to manufacture, or find manufacturers to be capable?Regards,Josh

author: hcglitte
author_rank: Regular Contributor
timestamp: February 15, 2017, 07:33:32 am
content: Do the tracks, escaping under the o-ring, cause leaks due to lack of flatness?Are the tracks covered with soldermask in the o-ring area?Have you considered other o-ring rubber materials?Could you use RTV silicone instead? Using this would require that you apply it before attaching the PCB to the enclosure.RTV is a silicone glue.

author: Helix70
author_rank: Unknown
timestamp: February 15, 2017, 08:43:16 am
content: Thanks for the reply. I am looking for information regarding the PCB and via options. The sealing methods are tried and tested, and we prefer not to modify these. The PCB is masked.

author: Kean
author_rank: Unknown
timestamp: February 15, 2017, 11:25:15 am
content: I don't have any specific info on via filling, but I'm certainly interested in this discussion.I'm in the process of revising a design for a wildlife tracker that will ideally have a similar configuration. I had pretty much decided I would need to use a wide rubber gasket rather than an o-ring, and keep any vias away from the connecting pads. Or just filling the area with a silicone compound.I was also still deciding on whether to use the bare PCB pads (should it have "hard gold"/finger plating?), or a pogo target connector (costly, but "fills" the enclosure cutout).

author: DerekG
author_rank: Frequent Contributor
timestamp: February 15, 2017, 12:51:29 pm
content: You state:Quote from: Helix70 on February 15, 2017, 06:26:48 amYou then state:QuoteSo it is not IP68 rated.Whilst you may be looking for a cheap way to seal your unit, relying on what you have already told us would indicate that your design is poor.You may not wish to hear this, but the proper way to maintain an IP68 rating is to use a professional connector that is specifically designed to meet this standard.

author: vealmike
author_rank: Regular Contributor
timestamp: February 15, 2017, 12:57:31 pm
content: Assuming the o-ring is leaking because the PCB underneath isn't flat, there are a number of alternatives to vias that might be easier / better suited.1/ change o-ring materialto be me conformative.2/ increase o-ring clamping force.3 / Make PCB flatFor 3, consider flooding the area under the O-ring with copper using GND fill. Now instead of a bump for the traces, you have a small dip where there is a gap between your trace and the GND fill - with a small gap and a conformal coat, this should be flatter.HTH.

author: HHaase
author_rank: Regular Contributor
timestamp: February 15, 2017, 01:04:48 pm
content: I completely agree with Derek;If the presence, or non-presence, of via's is causing you waterproofing issues than it's more of a design factor than production method. Realistically you should designate a 'keep out' area where traces and via's are not permitted on the sealing side. This way you don't have holes going through or traces that cause surface irregularities. Even better would be a sealed plug-in style bulkhead connector that is waterproofed on each individual connection. Hard to give specific recommendations without knowing the design better.I would also say that if your pogo pin connections have a potential to get wet, than you have other issues to deal with. Gold plating may help with oxidation of the pad location but there are other problems to consider. FR4 can and does absorb water if conditions are right, which causes all sorts of issues from swelling and delamination, all the way to high voltage arcing due to the material being waterlogged. Plus you have the potential of water causing shorts between pins/traces if they're exposed to water.If a redesign is not possible or too costly, another option to consider is manually soldering the via's shut.Are you doing any kind of conformal coating after manufacture?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 15, 2017, 08:14:00 pm
content: Well if you truly want filled vias -- you probably want epoxy filled, planarized and capped (covered with plating). This is almost invisible on the finished PCB. The pad is a solid SMT pad surface, usually with a barely-perceptible dimple in the center, where the hole was filled in.You can also get conductive fill, which might be better for high current or thermal vias.Very small vias can also be plated shut, but I would expect these to have microscopic defects making them unsuitable for sealing purposes.Fill isn't very expensive, as far as I know, but it does require added steps, and it's not a standard prototype service, so it will be expensive (from a US board house, for the initial proto run, about a kilobuck or two).Tim

author: Helix70
author_rank: Unknown
timestamp: February 15, 2017, 08:47:39 pm
content: The opinions on the design are noted. Of course alternate sealing methods will be considered by the mechanic eng. I am still interested in a comparison of the via filling methods from the original post.Sent from my iPhone using Tapatalk

author: Helix70
author_rank: Unknown
timestamp: February 15, 2017, 08:49:54 pm
content: Quote from: T3sl4co1l on February 15, 2017, 08:14:00 pmThanks for the post. Not concerned about proto costs, the boards will become volume.Sent from my iPhone using Tapatalk

author: Helix70
author_rank: Unknown
timestamp: February 15, 2017, 08:51:44 pm
content: Quote from: vealmike on February 15, 2017, 12:57:31 pmYes, I have considered the ground plane under the seal, it might work for us, yet to be tested.Sent from my iPhone using Tapatalk

author: vealmike
author_rank: Regular Contributor
timestamp: February 16, 2017, 08:11:44 am
content: Quote from: Helix70 on February 15, 2017, 08:49:54 pmYou're aware that glass fibre PCBs are hydroscopic right?Depends on your market model I guess and how often the product will get dunked. If the product has a limited lifespan and is considered a throwaway part you probably don't care. If you're selling hundreds of thousands with five year warranties then you definitely do.

author: Helix70
author_rank: Unknown
timestamp: February 16, 2017, 08:16:33 am
content: Quote from: vealmike on February 16, 2017, 08:11:44 amNot exposed to water, just need it to be air tight. Besides, the solder mask isn't.Does any one know anything about vias? Seems everybody is far more interested in the problems I didn't ask about and don't have.Sent from my iPhone using Tapatalk

author: vealmike
author_rank: Regular Contributor
timestamp: February 16, 2017, 12:05:00 pm
content: Quote from: Helix70 on February 16, 2017, 08:16:33 amIP68 denotes continuous immersion in >1m water. With respect, if you didn't intend immersion you've led us up the garden path with your IP68 statement.Quote from: Helix70 on February 16, 2017, 08:16:33 amAgreed it isnt. I'll wager that your PCB manufacturer will take a lot of convincing to use solder mask aperture smaller than your gold contact pads though.Quote from: Helix70 on February 16, 2017, 08:16:33 amOK, sorry for attempting to help, I won't do it (to you) again.Quote from: Helix70 on February 16, 2017, 08:16:33 amHonestly, I couldn't care less.

author: Helix70
author_rank: Unknown
timestamp: February 16, 2017, 12:11:50 pm
content: Not really, I was pretty specific. Wanted to know what people knew about vias. My iPhone is IP rated, though no one really touts it as a submersible phone.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 16, 2017, 03:06:05 pm
content: IP ratings span many kinds, from IIRC the IP2x range which is basically nothing, to IP67? that's the most strict (unless there's an extreme depth option?).The only "IP rated" thing is a network adapter. Without the numbers, it's meaningless.Tim

author: elecman14
author_rank: Unknown
timestamp: February 16, 2017, 03:06:43 pm
content: Quote from: Helix70 on February 16, 2017, 12:11:50 pmThey actually use that in the marketing for the phone I have. In the ad it goes into multiple situations including full submersion.Now on to what op is asking:Which style vias/PCB will be cheaper?If you are curious on the price difference of the different via technologies then just quote the four PCBs at volume. My gut tells me that plugged vias will be the cheapest and buried vias will probably be the most expensive. Again this really depends on the application. You may be able to spin a smaller PCB if you go 4 layers with buried vias.Which will be most reliable?You really have not talked about the environment or device life cycle this PCB will be subjected to. This can be determined by testing. Buy all four types and subject them to aggressive environmental aging. This will also very dramatically with material types.Which will be easiest to manufacture, or find manufacturers to be capable?Quoting the four types again will tell you. Since you did not really specify what industry this if for it really depends. A generic commercial PCB suppliers you would go to for a cheap product capabilities will be different than a supplier you would go to for automotive or aerospace.

author: Helix70
author_rank: Unknown
timestamp: February 17, 2017, 02:08:09 am
content: Quote from: elecman14 on February 16, 2017, 03:06:43 pmThanks for the reply. Of course testing all options would be desirable, but since time and money are always limited, I was hoping for some experience from others to narrow the field a bit.Here is a bit more background. Maintaining the internal moisture levels to "very low" is desired. Desiccant is fitted internally during manufacture, and the device is submerged for leak testing. This ensures a dry environment inside the unit. It is a 15 year product in an outdoor environment. It is not our first.We have previously used a PCB with gold pins soldered to it to interface power and comms to the outside world, but never needed to run tracks under the seal, as the pins are through hole. In an effort to improve the BOM cost and ease of manufacture, the one time use comm port interface has been designed onto pads instead of gold pins, in the same area that the gold power pins are located. A battery connects to this location, and covers it, but doesn't seal it airtight, just shields it from direct exposure to light, dust and rain. Moisture does not pool in this area, it is designed to dry following high humidity.This design is in use in another 15 year product. The BOM cost is low, the parts always engage correctly, and we already have the pins (albeit a few bucks a mating pair). The new parts are the use of pads for the factory load (pogo pins on the factory loader - low volume), and the tracks routing under the seal if no vias are used. All other issues regarding the use of the pins, FR4's hygroscopic properties (which is practically non existent by the way - it is an excellent insulator and absorbs very little moisture -https://en.wikipedia.org/wiki/FR-4), the seal material and clamping force of the seal, have been tested and work as designed. Re-engineering is expensive.I am nervous about the pads, hard gold plated or not, i think salt fog testing will kill these, even though these pins are not powered after the initial load. We will see.The Mech Eng is nervous about the long term seal if there are tracks running under the seal. Hard to test in a short amount of time. We would prefer to avoid than test this.That is what lead to my specific request for experience with alternatives for the tracks (ie via options). Truth is, if the pads are a no go, I will probably use IrDA from inside the sealed area and the sealing problem disappears, but would prefer to keep it simple for both hardware and firmware.

author: elecman14
author_rank: Unknown
timestamp: February 23, 2017, 01:11:25 pm
content: Quote from: Helix70 on February 17, 2017, 02:08:09 amIf you are worried about the pads having some sort of electromigration you could look into a peelable mask if you ever need to re-flash or conformal coat if field re-flashing is not needed.

author: richardlawson1489
author_rank: Regular Contributor
timestamp: February 24, 2017, 07:15:48 am
content: Check out the Blog and discussion below. This would be helpful.http://www.eetimes.com/author.asp?doc_id=1320862

author: Helix70
author_rank: Unknown
timestamp: February 24, 2017, 07:38:31 am
content: Good link. Thanks for sharing.