removing bits from tStop

Olin Lathrop wrote:

only for careless board houses. Serious manufacturers know the risks.

 

Take a look at most circuit boards, and you will see the vias covered with

soldermask.

the good ones are not covered with solder resist but plugged (a

separate processing), the bad ones are simply bad.

Apparently someone here had a bad day possibly caused by dirt

trapped under the soldermask which then corroded the via.  Yes, I suppose

Where should "dirt" come from?

If something is trapped in those vias then likely chemicals from the

board processing, uncured resist.

With open vias, the surface finish (HAL, immersion Tin etc.) also

coats and protects the via and drives away the residues of the

previous processing. Solder resist over the via hole prevents this so

you get bare Copper contaminated with some chemicals. And you don't

get reliably closed holes, so it could be that humidity enters the

via, forming some even more critical mixture.

careless board houses can run into that, but that doesn't make the overall

concept wrong.

 

I once had a problem with a run of boards that failed months after getting

into the field.  This was eventually traced back to sloppy board

manufacture.  A connector was used with relatively fine pitch, 1.25mm if I

remember right.  The PCB material was not made correctly, so there were

small voids in it.  Chemical residue got stuck in the voids, which over

time either shorted out adjacent pins directly or caused metal atoms to

migrate which then caused shorts.  Some were only a few ohms between

Maybe "conductive anodic filaments" (CAF) often happening with bad

laminate.

Anyway, the point is stuff goes wrong, but don't blame it on the wrong

thing or believe in mythological solutions.  What you're saying about the

solder mask is like saying I should never use a 1.25mm connector again

because one board house made bad PCBs that run.  Clearly that would be

silly.

It's silly to be reluctant to gather information about the problem and

insist on writing that solder resist covered vias are o.k.

Please do use solder resist covered vias in your products as you like,

but don't tell other people that it is correct to do so.

Oliver

Olin Lathrop wrote:

only for careless board houses. Serious manufacturers know the risks.

 

Take a look at most circuit boards, and you will see the vias covered with

soldermask.

the good ones are not covered with solder resist but plugged (a

separate processing), the bad ones are simply bad.

Apparently someone here had a bad day possibly caused by dirt

trapped under the soldermask which then corroded the via.  Yes, I suppose

Where should "dirt" come from?

If something is trapped in those vias then likely chemicals from the

board processing, uncured resist.

With open vias, the surface finish (HAL, immersion Tin etc.) also

coats and protects the via and drives away the residues of the

previous processing. Solder resist over the via hole prevents this so

you get bare Copper contaminated with some chemicals. And you don't

get reliably closed holes, so it could be that humidity enters the

via, forming some even more critical mixture.

careless board houses can run into that, but that doesn't make the overall

concept wrong.

 

I once had a problem with a run of boards that failed months after getting

into the field.  This was eventually traced back to sloppy board

manufacture.  A connector was used with relatively fine pitch, 1.25mm if I

remember right.  The PCB material was not made correctly, so there were

small voids in it.  Chemical residue got stuck in the voids, which over

time either shorted out adjacent pins directly or caused metal atoms to

migrate which then caused shorts.  Some were only a few ohms between

Maybe "conductive anodic filaments" (CAF) often happening with bad

laminate.

Anyway, the point is stuff goes wrong, but don't blame it on the wrong

thing or believe in mythological solutions.  What you're saying about the

solder mask is like saying I should never use a 1.25mm connector again

because one board house made bad PCBs that run.  Clearly that would be

silly.

It's silly to be reluctant to gather information about the problem and

insist on writing that solder resist covered vias are o.k.

Please do use solder resist covered vias in your products as you like,

but don't tell other people that it is correct to do so.

Oliver