Does anyone know what this means (email text from pcb house) - Page 1
Forum section: electronics / general

author: Psi
author_rank: Super Contributor
timestamp: January 12, 2012, 05:31:59 am
content: I have a pcb with some 0.7mm and 0.9mm holes, there are copper pads on the bottom layer but no pads on the top layer.And i would like them to be non plated.I just received this email from the company questioning how to proceed and i'm not sure exactly what they mean.I can email them back and ask but that will add another day to the process since they only answer emails once a day.Here is the email text."0.7mm and 0.9mm holes have only 1 side pads, if to do them non plated, we need to chip off copper around the holes in bottom layer, ok? If not, we will do them plated and add copper pads in top layer."I understand the 2nd option. Adding copper pads to the top layer. But does anyone know what they mean by "chip off" ?

author: slateraptor
author_rank: Frequent Contributor
timestamp: January 12, 2012, 05:56:34 am
content: My guess is somehow manually removing the annular ring on the bottom copper.EDIT: Maybe I'm misunderstanding something here. Your description and what the board house wants to do sounds opposite.

author: Psi
author_rank: Super Contributor
timestamp: January 12, 2012, 06:24:56 am
content: i talked it over on irc with someone and what we think they mean is that they cannot do copper right up to the edge of a non plated hole.So they need to 'chip off' some of the copper around the hole in order to make it non-plated.So the bottom pads would then have a gap between where the inner copper ring ends and the hole starts.

author: Rufus
author_rank: Super Contributor
timestamp: January 12, 2012, 11:51:21 am
content: Quote from: Psi on January 12, 2012, 05:31:59 amDoing what you want requires those holes to be drilled after the board has been processed. Helpful to supply a separate drill file for them and it is an extra process step unless the board profile is routed and they can drill at the same time.They seem to be offering to (try to) fill those holes with resist prior to plating which will require some resist on the copper around the hole and that copper will get etched away later.In case you are not aware of the process, photo resist is used to resist plating not etching. Copper is plated where there is no resist (including down the holes). A layer of tin is plated on the copper and the photo resist stripped away. The tin is what resists etching.

author: Jon Chandler
author_rank: Frequent Contributor
timestamp: January 12, 2012, 11:38:32 pm
content: Quote from: Rufus on January 12, 2012, 11:51:21 amThis isn't usually the case. A board starts as a copper-covered sheet. Resist is applied and unwanted copper is etched away. Next, the holes are drilled and then electroplated.If there's not annular rings on both sides of the board, the plated material in the holes may not bond well and can break free.This is from Triangle Circuits web page:Quote

author: Psi
author_rank: Super Contributor
timestamp: January 13, 2012, 01:22:43 am
content: i ended up talking to the pcb house and we decided the best option was to add tiny pads to top layer so the holes can be plated as normal. Then have the pads tented on the top layer so solder mask covers them upThat way i get what i want, (no gold pads on the top of the pcb) and they can plate them as normal.Thanks to everyone who helped.

author: Rufus
author_rank: Super Contributor
timestamp: January 13, 2012, 02:38:21 am
content: Quote from: Jon Chandler on January 12, 2012, 11:38:32 pmYou can't electroplate an etched board because electroplating requires an electrical connection to what you are plating.The Triangle Circuits description is too vague. The board and holes are electroplated before any etching. Photo resist is used to avoid plating copper you will etch away later. The copper is then plated with tin to act as an etch resist. The photo resist is then stripped and the board etched to remove the copper which was covered by photo resist.