how to validate that a unit is sealed
how to validate that a unit is sealed
(OP)
Our products generally consist of a PCB assembly that gets sealed in a plastic enclosure (roughly 8"x4"x1.5") via a hot-plate welding operation. Our current method of verifying that the welding operation produced a fully sealed unit is to heat the sealed product for a period of time sufficient to build internal pressure that causes the product to expand - the 1.5" dimension increases. This is a time consuming process that we're trying to revise or eliminate. Additionally, our new products are continually getting smaller so even if we wanted to stick with the same test method the amount of "puff" seen in the new enclosures is pretty minimal, making evaluation difficult.
We have proven that we can perform the same test by evaluating the units in a vacuum bell, but the equipment is quite expensive and there is resistance to going this route.
Does anyone have any other suggestions as to how we can perform this testing? Obviously fast and inexpensive are preferable, but at least we don't need a solution immediately.
Thanks in advance.
We have proven that we can perform the same test by evaluating the units in a vacuum bell, but the equipment is quite expensive and there is resistance to going this route.
Does anyone have any other suggestions as to how we can perform this testing? Obviously fast and inexpensive are preferable, but at least we don't need a solution immediately.
Thanks in advance.





RE: how to validate that a unit is sealed
RE: how to validate that a unit is sealed
We've toyed with that idea, or something similar, but didn't go too far because of cost. In any case, thanks for the suggestion.
Additional useful information for anyone else thinking about this is that the devices will be made by the millions and of course are cost-sensitive.
RE: how to validate that a unit is sealed
Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services
www.infotechpr.net
RE: how to validate that a unit is sealed
RE: how to validate that a unit is sealed
But I would still do a spot check from time to time....
RE: how to validate that a unit is sealed
TTFN
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RE: how to validate that a unit is sealed
Dry air should be fine.
Nitrogen is an asphyxiation hazard and requires special precautions.
Mike Halloran
Pembroke Pines, FL, USA
RE: how to validate that a unit is sealed
Tobalcane
"If you avoid failure, you also avoid success."
RE: how to validate that a unit is sealed
But I'm sure a competent mechanical engineer with access to machine shops could build and/or buy equipment to make a vacuum chamber "tool", complete with quick-clamp lid, integral displacement sensor and a high-speed vacuum pump, for not too much money.
Even cheaper if you just use shop air and go the overpressure test route, though you then need to be more careful about the chamber design due to explosion/rupture risks.
RE: how to validate that a unit is sealed
RE: how to validate that a unit is sealed
RE: how to validate that a unit is sealed
With this method you get reliable results in seconds. If you are measuring case expansion it is very difficult to detect small leaks. Pressure loss takes time and temperature changes during this time will conceal a leak.
RE: how to validate that a unit is sealed
TTFN
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RE: how to validate that a unit is sealed
IRstuff, agreed on the acceptance criteria.
RE: how to validate that a unit is sealed
dip 100 of them in a pressurized water tank
Reweigh them
any that gained weight leaked
pressure will need to be low enough to not create leaks but high enough to go inside.
RE: how to validate that a unit is sealed
Have you considered adding a pressure sensor internally? Then, you could easily pressure bomb the case and see what the readings look like afterwards.
TTFN
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RE: how to validate that a unit is sealed
...or the plastic case absorbed water.
RE: how to validate that a unit is sealed
Things are never as simple as they look.
dgowans please let us know if anything works.
RE: how to validate that a unit is sealed
We had to do that, once, on a munition with a leaky coolant vessel; was looking for a fraction of an ounce change in a 30 lb unit.
TTFN
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RE: how to validate that a unit is sealed
RE: how to validate that a unit is sealed
1. a single bad unit may not register enough change in the group reading to reject the lot.
2. if small numbers of bad units do register within the lot test, you need a way to single out the bad units to find the leakers, or else reject the whole lot. This can be much more expensive.
Better to find a fast, efficient, single-item test. It can then be applied on a sampling basis...
RE: how to validate that a unit is sealed
RE: how to validate that a unit is sealed
Helium testing is not effective with larger leaks, as most of the helium will escape before you transfer the part to the detector. Hence the use of the bubble test, using Galden to test it at 125°C.
So I'll add another voice suggesting acceptance criteria; this will make clear what testing is needed. You can check the mil-specs to help come up with one.
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