<div dir="ltr"><div dir="ltr"><div>Hi Nathanael,</div><div><br></div><div>I had a similar situation in which I couldn't use our hot phos station for initial fear of cross contamination, so I set up a hotplate process at our general wet bench.</div><div><br></div><div>First you need a quartz beaker since pyrex will be damaged over time (even after one use). I used a 1L beaker. Unfortunately they aren't cheap.</div><div><br></div><div>I put the beaker in a metal pan (dry) as containment in case of spillage or worst case a crack in the beaker. I found at 350C the hot phos in the beaker, through the metal pan, would reach a stable 160C (but you'll have to determine your own hot plate settings). I covered the beaker with a teflon dish. The spout or beak of the beaker allows vapour to escape. It is also perfect to put a thermometer in (good to over 160C of course) to monitor the temperature. The spout also allows you to occasionally squirt small quantities of DI in to maintain concentration. Don't go nuts since you're technically breaking the AAA rule.</div><div><br></div><div>The die should be placed in a teflon basket for controlled submersion since they will tend to float. Also when the etch is complete it makes it easier to remove the die to be washed with DI. Turn the hotplate off and let the beaker cool so you can aspirate or otherwise safely dispose of the phosphoric acid.</div><div><br></div><div>It's not the most repeatable setup, but it worked nicely if you don't have a proper heated phosphoric acid bath with DI dripper and N2 bubbler. Of course, you should wear full PPE during the process.</div><div><br></div><div>-Chris</div><div>
<span class="gmail_signature_prefix">-- </span><br><div dir="ltr" class="gmail_signature"><div dir="ltr"><div></div><div>Quantum Fabrication Engineer - R&D4</div>Quantum Nanoelectronics Laboratory<br>University of California, Berkeley<br>125 LeConte Hall<br>Berkeley, CA. <br>Email: <a href="mailto:craum@berkeley.edu" target="_blank">craum@berkeley.edu</a></div></div>
<br></div></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Mon, Apr 20, 2026 at 6:59 PM Nathanael Sieb <<a href="mailto:sieb@4dlabs.ca">sieb@4dlabs.ca</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><u></u>
<div>
<p>Hi Lorenzo,</p>
<p>Thanks for your detailed feedback and this was along the lines of
my expectations. Have you or anyone else seen any self-contained
table-top baths that would fit on top of a wet-bench deck? Most
of what I've seen is deck-mount in a wet bench or a heater-chiller
designed to heat or cool a bath but not contain chemicals.</p>
<p>Does anyone do this safely without using an acid bath permanently
built into a wet bench? I'm guessing the answer is mainly no, but
I figured I'd check.</p>
<p>Thanks,</p>
<p>Nathanael</p>
<p><br>
</p>
<div>On 2026-04-19 9:35 a.m., Lorenzo
Palmiano wrote:<br>
</div>
<blockquote type="cite">
Here are some tips, OSHA and SDS also breaks down all the safety
pre-cautions is 5 parts: engineering, handling, storage, PPE and
emergency response.
<div><br>
</div>
<div>
<p style="margin:0px 0px 12px;font-style:normal;font-variant-caps:normal;line-height:normal;font-family:system-ui;font-size-adjust:none;font-kerning:auto;font-variant-alternates:normal;font-variant-ligatures:normal;font-variant-numeric:normal;font-variant-east-asian:normal;font-feature-settings:normal">
At ~160 °C, phosphoric acid is highly viscous and near
boiling. Risks include increased splashing and bumping, higher
aerosol or acid mist generation, and severe combined thermal
and chemical burns from any contact.</p>
<p style="margin:0px 0px 12px;font-style:normal;font-variant-caps:normal;line-height:normal;font-family:system-ui;font-size-adjust:none;font-kerning:auto;font-variant-alternates:normal;font-variant-ligatures:normal;font-variant-numeric:normal;font-variant-east-asian:normal;font-feature-settings:normal">
<span style="font-weight:bold">1. Equipment and Temperature
Control</span><br>
• Use only a temperature‑controlled acid bath or certified wet
etch bench<br>
• Do not use open beakers on generic hot plates<br>
• Verify bath temperature with an independent thermometer or
probe<br>
• Avoid overshoot above setpoint; local overheating increases
instability<br>
• Never leave heating unattended</p>
<p style="margin:0px 0px 12px;font-style:normal;font-variant-caps:normal;line-height:normal;font-family:system-ui;font-size-adjust:none;font-kerning:auto;font-variant-alternates:normal;font-variant-ligatures:normal;font-variant-numeric:normal;font-variant-east-asian:normal;font-feature-settings:normal">
<span style="font-weight:bold">2. Water Exclusion (Zero
Tolerance)</span><br>
• Absolutely no DI water near the bath while hot<br>
• No wet wafers, tools, or condensation introduction<br>
• Do not add water to hot acid under any circumstances<br>
• Any water contact at this temperature can cause violent
splattering</p>
<p style="margin:0px 0px 12px;font-style:normal;font-variant-caps:normal;line-height:normal;font-family:system-ui;font-size-adjust:none;font-kerning:auto;font-variant-alternates:normal;font-variant-ligatures:normal;font-variant-numeric:normal;font-variant-east-asian:normal;font-feature-settings:normal">
<span style="font-weight:bold">3. Required PPE at ≥160 °C</span><br>
• Chemical splash goggles AND full face shield (both required)<br>
• Acid‑resistant apron (front facing out)<br>
• Long acid‑resistant gloves with arm shields<br>
• Standard safety glasses alone are not sufficient<br>
• Do not use stained, wet, cracked, or poorly fitting PPE</p>
<p style="margin:0px 0px 12px;font-style:normal;font-variant-caps:normal;line-height:normal;font-family:system-ui;font-size-adjust:none;font-kerning:auto;font-variant-alternates:normal;font-variant-ligatures:normal;font-variant-numeric:normal;font-variant-east-asian:normal;font-feature-settings:normal">
<span style="font-weight:bold">4. Positioning and Handling
Discipline</span><br>
• Never lean over the bath<br>
• Approach from the side, not directly from the front<br>
• Move slowly to avoid wave‑induced splashing<br>
• Treat all clear liquids as hot acid — never assume it is
water</p>
<p style="margin:0px 0px 12px;font-style:normal;font-variant-caps:normal;line-height:normal;font-family:system-ui;font-size-adjust:none;font-kerning:auto;font-variant-alternates:normal;font-variant-ligatures:normal;font-variant-numeric:normal;font-variant-east-asian:normal;font-feature-settings:normal">
<span style="font-weight:bold">5. Ventilation and Airflow</span><br>
• Operate only with confirmed functioning exhaust<br>
• If airflow or power is lost, stop work immediately and leave
the area<br>
• Hot phosphoric acid fumes and mist present inhalation
hazards</p>
<p style="margin:0px 0px 12px;font-style:normal;font-variant-caps:normal;line-height:normal;font-family:system-ui;font-size-adjust:none;font-kerning:auto;font-variant-alternates:normal;font-variant-ligatures:normal;font-variant-numeric:normal;font-variant-east-asian:normal;font-feature-settings:normal">
<span style="font-weight:bold">6. Emergency Readiness
(Before Starting)</span><br>
• Know the exact location of the eyewash and safety shower<br>
• Be prepared to cut heater power immediately if needed<br>
• In case of skin or eye exposure, flush with water for at
least 15 minutes and seek medical attention</p>
<p style="margin:0px 0px 12px;font-style:normal;font-variant-caps:normal;line-height:normal;font-family:system-ui;font-size-adjust:none;font-kerning:auto;font-variant-alternates:normal;font-variant-ligatures:normal;font-variant-numeric:normal;font-variant-east-asian:normal;font-feature-settings:normal">
<span style="font-weight:bold">Bottom Line</span><br>
At ~160 °C, hot phosphoric acid must be treated as
near‑boiling corrosive material. Strict temperature control,
zero water exposure, full PPE, proper ventilation, and
disciplined handling are mandatory.</p>
<p style="margin:0px 0px 12px;font-style:normal;font-variant-caps:normal;line-height:normal;font-family:system-ui;font-size-adjust:none;font-kerning:auto;font-variant-alternates:normal;font-variant-ligatures:normal;font-variant-numeric:normal;font-variant-east-asian:normal;font-feature-settings:normal">
Please follow these precautions without exception.</p>
</div>
<div><br id="m_-124504167001390440lineBreakAtBeginningOfSignature">
<div dir="ltr">Lorenzo P
<div>415.404.0565</div>
<div><a href="http://www.espie-electronic.com" target="_blank">www.espie-electronic.com</a></div>
</div>
<div dir="ltr"><br>
<blockquote type="cite">On Apr 19, 2026, at 7:23 AM, Nathanael
Sieb <a href="mailto:sieb@4dlabs.ca" target="_blank"><sieb@4dlabs.ca></a> wrote:<br>
<br>
</blockquote>
</div>
<blockquote type="cite">
<div dir="ltr">hot phosphoric acid etching in your facilities,
I would appreciate any safety or operational tips you have.
For us it would need to be a hot-plate process, and I want
to make sure we are taking a cautious approach before
allowing heating of phosphoric up to 160°C.</div>
</blockquote>
</div>
</blockquote>
<div>
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