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Thread: I think I'm more worried about tented

28 Discord messages from 📐 - Designing/📦-cob/threads/i-think-im-more-worried-about-tented.md.

Category: 📐 - Designing Parent channel: #📦-cob Thread ID: 1535364727167783036

Messages: 28

message-1535365908892229712

2026-08-07T19:15:58.399+00:00 — Essen (@essen__)

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message-1535365912905916467

2026-08-07T19:15:59.356+00:00 — Essen (@essen__)

Content

> I'm more worried about tented vias than fully open ones at least if they're thin enough for the epoxy to not just drip down;
Not sure what you mean there, are you more worried about them being tented ? And if so, doesn't tented imply there is no dripping because the hole is closed ?

Also, if you remember (I am still in the process of re-reading the entire thread), why where the via's tented only on one side in the first place ?
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message-1535368350773813338

2026-08-07T19:25:40.589+00:00 — namibj

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If they're tented that means there could be air enclosed beneath that could vapor going up rather than down.
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message-1535368444986531930

2026-08-07T19:26:03.051+00:00 — namibj

Content

The tented side didn't have an area of exposed ground plane
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message-1535368564180258957

2026-08-07T19:26:31.469+00:00 — namibj

Content

(The chip was placed on and surrounded by a golden shiny ground plane that was exposed.)
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message-1535370159341178893

2026-08-07T19:32:51.785+00:00 — Essen (@essen__)

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Perfect, I was supposed to read it that way, we are aligned in our understanding 👌
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message-1535379186993209485

2026-08-07T20:08:44.145+00:00 — Essen (@essen__)

Content

> For reliability IMO we should at least ask if they have a generic CTE-vaguely-matched loaded version available given that I don' think they'd require actually different processing beyond dosing the epoxy from the other dispenser.
Also not sure what you mean here. I follow up to CTE (Coefficient of thermal expansion) and I have a vague understanding of how that would impact our bond finger design, but you lost me at "-vaguely-matched loaded version available given that I don' think they'd require actually different processing beyond dosing the epoxy from the other dispenser."
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message-1535379285429321748

2026-08-07T20:09:07.614+00:00 — Essen (@essen__)

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> Might be contingent on the tracability serial being included, though; in case they fall down after globbing and are all mixed up between projects somehow.
We already have the qrcodes though.
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message-1535379996997189752

2026-08-07T20:11:57.265+00:00 — Essen (@essen__)

Content

Thermal management already looks pretty good (filled gnd plane), and apart from adding parts like heatsinks that would increase the BOM cost I don't think there is much to be done on that panel.
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message-1535380521788641300

2026-08-07T20:14:02.385+00:00 — Essen (@essen__)

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Thinking about it, I think the more effective approach for thermal management right now we be to add a fan to the pcb for chips for which that was a problem. 🤔
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message-1535385638097002556

2026-08-07T20:34:22.208+00:00 — namibj

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So normal glob tops are black
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message-1535385719290335323

2026-08-07T20:34:41.566+00:00 — namibj

Content

The Run1 ones were clear
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message-1535386009297227839

2026-08-07T20:35:50.709+00:00 — namibj

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They would not be visible under an opaque glob that is loaded with some substance that makes the composite (epoxy and whatever they load it with) behave closer to silicon than it would naturally due.
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message-1535386376378515507

2026-08-07T20:37:18.228+00:00 — namibj

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How does the heat get away from the die proper? I mean like thermal vias as a concept but also keeping an eye on thermal expansion flexing and stressing the die attachment.
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message-1535390200153505823

2026-08-07T20:52:29.887+00:00 — Essen (@essen__)

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That is actually great news in terms of permeability.
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message-1535391311727693866

2026-08-07T20:56:54.907+00:00 — Essen (@essen__)

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Valid point there.
Frankly I have no idea how I could even simulate that for evaluation, so I will be reading up on the literature on that one and making a best effort.
Else, my mini test program, renaming it to my "torture test suite" should include thermal cycling, though that would be logistically much more challenging than what I had planned.
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message-1535391644126421055

2026-08-07T20:58:14.157+00:00 — Essen (@essen__)

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Do you recall why we want that in the first place ?
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message-1535391988470517760

2026-08-07T20:59:36.255+00:00 — namibj

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probably the die attach wanted it and the gnd bond ring and then they felt like filling the space to the board-side pad ring with it as well and put the ground vias there
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message-1535393819116179497

2026-08-07T21:06:52.715+00:00 — Essen (@essen__)

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But why the through holes though ?
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message-1535393926926827611

2026-08-07T21:07:18.419+00:00 — namibj

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idk

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message-1535395014027247696

2026-08-07T21:11:37.604+00:00 — Essen (@essen__)

Content

Thanks for everything, I will be looking at adding the thermal vias for sure once I absorb about 300 more pages of literature on the topic to make sure and not trip over a rock 100s have already tipped over.
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message-1535398415159009380

2026-08-07T21:25:08.497+00:00 — namibj

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well see I'm not sure that copper/holes is good for the balance of thermal resistance and CTE-match
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message-1535408049135681538

2026-08-07T22:03:25.416+00:00 — Essen (@essen__)

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Copper hole defiantly not a good idea.

But apparently filled and copper caped vias are recommended.

I will have to see who that impacts unit cost though.
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message-1535410038615572541

2026-08-07T22:11:19.745+00:00 — namibj

Content

copper capped? You mean epoxy-filler-and-plated-over-vias?
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message-1535410179372482651

2026-08-07T22:11:53.304+00:00 — namibj

Content

Those are available on the 6L process of JLC as default IIRC.
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message-1535418389097357323

2026-08-07T22:44:30.655+00:00 — Essen (@essen__)

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Apparently there is a thing such as copper filled to. But epoxy filled might still work.
Do you recall if the PCB are made at JLC ?
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message-1535426587577552896

2026-08-07T23:17:05.325+00:00 — namibj

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they have been made there so far; they do offer very competitve pricing for the needs so far.
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message-1535426701398646844

2026-08-07T23:17:32.462+00:00 — namibj

Content

Copper filled is expensive-ish NRE wise for testing; might not matter much for series though.

Reactions

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