Challenges in waterproofing electronics assembly.
Today we are looking at how we design for testing by focusing on the IP 67 water column test.
When dealing with consumer electronics, you typically try to minimize the number of parts and make it easy to put them together. Consistency and repeatability is important and you’re often avoiding glues. If just rain proofing is your goal, this is easy to achieve. But when you get into submersion, you have to worry about seals and how parts are assembled. For instance, do you have a proper amount of compression for the O-Rings? Will the materials supporting the O-Rings support the seal over time?
If using an element, make sure that that it has a continuous bead of even pressure all the way around. That can be hard to generate if you're working with tight corners, or if dealing with butt joints where surfaces flex apart in certain areas. You might, for example, have good compression in one spot, while another has leaking areas.
In past testing, we've had problems on the assembly line where even a human hair can get across the ceiling path and cause water to leak through. So, you need to make sure that it's easy to assemble consistently, and that assembly is done in a clean environment.
Aging of plastics can also cause products to deflect over time and leak. Be clear on whether you're testing just at the start of the product cycle. To account for the plastics tendency to relax over time you want to age the assembly before you run the testing.
You must make sure that if you're pushing, you can't just push harder to get a better seal. With plastics, if you push harder, they will flex out of the way, and you can compromise the seal. Metals are more stable and will allow for harder pressure to achieve seal.
IP67 water resistance testing for consumer products.
IP67 is a common a common rating for consumer product devices. The IP stands for Ingress Protection and the first number refers to particle while the second number refers to moisture. Specific to water resistance the particle is often skipped and the rating is referred to as IPX7.
In this case, seven means, “one meter underwater for 30 minutes of time.” Compared to some of the lower standards that are built around rainwater and directional splashing, this one focuses on submersion. The product must survive functionally and, as a general standard, not have any water get inside of the device.
Steps in the IPX7 Water Column test
1. Take a one-meter column and fill with water.
2. Sink the device being tested to the bottom of the column.
3. Leave it there for half an hour.
4. Take it out and inspect to see if it's still functional.
5. Examine to see if it has any water inside.
In this example I am using a pencil white, or black diamond. I use fishing wire to make it easy to recover the device. Then wait thirty minutes and pull it out.
Check the device is functional.
IPX7 requirements state that the device must be functional after it's removed from water. We often interpret that as no water inside the device, but I do want to check that it's functioning properly. Start by running it through the motions to check to see if everything's functioning as intended.
Some things take a little bit of time to dry out, like USB plugs. You want to make sure that those are free of water before you inspect them functionally. The standard is not necessarily that it operates underwater, but that it survives submersion.
Inspect for water ingress.
Next you need to determine if water got into the device. There are a few techniques for achieving this. The simplest is a visual inspection. You could also use a dye to see if water got in, or you can try using detecting tape.
Try to avoid getting any of the water outside into the device. I want to look and see if there's a presence of water, but don't want to worry about whether I brought water myself.
In this case, I found indications that water got in, but that doesn't necessarily fail this product. They may have designed it so that this battery compartment can get wet, and that the main electronics cannot. This is a decision to be made by the developer.
This battery portion of the device was not developed to be waterproof, as there is no sealing mechanism that would stop water from pushing through. One of the big differences between the lower IPs rain or splash resistance verses submersion is pressure. When you have a raindrop or spray, there's not a lot of pressure on the seals, but as soon as you get immersion the seal point has a lot of pressure on it.
Potential sources of water ingress
You are looking for water, and you should be 
especially interested in where the water got in. Look to see if there's any defects at the sealing points. Check for scratch marks from handling, and human hairs or debris. Look to see if the seal is consistent all the way around. If there is a rough textured surface, if there are witness lines in the plastic these can all provide places for ingress. Inspect anywhere there could be a break in that constant seal as it goes around.
Conclusion
IPX can have an increasing range of conditions, and almost always correlates to cost and effort to develop. IPX7 is a great start point for most consumer products – you know if it meets IPX7 incidental intrusion is covered. It’s also near the upper limit on the IP standard system, as there's not yet a clear standard about 68 as opposed to 67 which is very clearly defined. What the industry has interpreted for IPX8 is you either submerge it for twice as long, or you put it twice as deep, or both. Companies usually set their own policy on what it means and what constitutes a pass or fail.
The IPX7 test is very simple. But the inspection and getting it to pass is where work and effort goes. It takes attention to detail and well thought out design to get it to pass this inspection.
Let us know what tips you might have for improving the success rate of products in this test.