How to stop  - Page 1
Forum section: electronics / projects

author: Sruk
author_rank: Contributor
timestamp: April 10, 2014, 08:46:52 am
content: Greetings!In one of my projects I'm using 20pin SMT receptacle. This receptacle is a dual entry kind. Like on this photo below.The problem arises in the process of varnishing (lacquering) of the assembled PCB. Receptacles tend to drain the varnish (lacquer) into the connector holes, thus blocking the holes and preventing the connectivity. Even a small amount of the lacquer added to the bottom of the connector runs up into the holes.It most certainly relates to the viscosity of the varnish/lacquer and the hydrostatic effects.I need an advice how to prevent this issue. Is there any kind of rubber/nylon plug that could stop this process. Maybe a peel of mask or anything similar.Thx!

author: zapta
author_rank: Super Contributor
timestamp: April 10, 2014, 09:22:12 am
content: Cover them with adhesive tape?

author: poorchava
author_rank: Super Contributor
timestamp: April 10, 2014, 09:34:50 am
content: I think the OP means capillary forces sucking the lacquer up from underneath the connector.You can use selective coating (the kind that uses mask with apertures to avoid putting the coating in certain areas. This obviously requires the coating to be applied by spray, not by immersion

author: Sruk
author_rank: Contributor
timestamp: April 10, 2014, 09:35:18 am
content: @zaptaDo You think that adhesive tape would ensure enough sealing so that air inside couldn't escape from the "tube"?Any quality tape suggestion?!

author: VK3DRB
author_rank: Super Contributor
timestamp: April 10, 2014, 12:01:29 pm
content: Try Kapton tape. It is pricey though.If you were just doing it for a one-off prototype, try Blu Tack, or good quality Scotch tape providing there is no heat and the lacquer does not attach the material.

author: Tinkerer
author_rank: Frequent Contributor
timestamp: April 10, 2014, 10:31:25 pm
content: My company simply covers stuff in tape before conformal coating it to stop it from getting where it doesnt need to be.

author: David Hess
author_rank: Super Contributor
timestamp: April 10, 2014, 10:49:22 pm
content: In the past when I dealt with the same problem, either a different connector was selected or sealant was added along the bottom of the connector by hand before conformal coating. I have seen poorly designed sockets have this problem with solder as well.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 11, 2014, 04:34:50 am
content: I think selective conformal can also be applied by, essentially, 3D-printing a gel. No idea how much that costs or compares.Tim

author: sleemanj
author_rank: Super Contributor
timestamp: April 11, 2014, 04:56:41 am
content: What if you just plug a male header in before coating it to plug it up.

author: Sruk
author_rank: Contributor
timestamp: April 11, 2014, 06:24:25 am
content: Thx people!I'll make an experiment using various kind's of adhesive tapes over the top entry holes. If it sticks hard enough maybe it will create inner pressure thus blocking the capillary forces mentioned below. Hydrostatics FTW.@sleemanjWe've tried that it doesn't help. There are still some gaps in the receptacle big enough to suck the lacquer fluid in.

author: Jeroen3
author_rank: Super Contributor
timestamp: April 12, 2014, 09:28:07 pm
content: Maybe it is just as easy as removing solder resist below the connector to make the open space larger. Which will reduce how eager the fluid wants to creep in.And for the top cover, some brands offer a cap on top of those connectors.

author: kizzap
author_rank: Unknown
timestamp: April 13, 2014, 01:54:31 am
content: forgive me if this is a stupid question, but would it be possible to solder those components onafterthe coating process?the only other thought I had would be either blue tack, or maybe liquid electrical tape.

author: peter.mitchell
author_rank: Super Contributor
timestamp: April 13, 2014, 02:47:17 am
content: Use a different type of lacquer, one that dries or at least goes tacky quicker. That is how i have solved this in the past.

author: Sruk
author_rank: Contributor
timestamp: April 13, 2014, 02:44:49 pm
content: @kizzapThere is no such thing as stupid questionThe coating process must be done after soldering because the leads are from both outer sides of the connector body. Solder joints must be coated too with the rest of the PCB.