Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Cleaning PCB's after routing

David Newman

#15747

Cleaning PCB's after routing | 22 May, 1998

Hello, I am looking for suggestions for cleaning pcb's after the routing (fabrication) process. Keep in mind that these pcb do not have components intalled on them yet. We have considered pre-drilling the routing plunge points, but cost and capacity concerns do not make this an option. Lowering plunge parameters and alternative routing cutter styles only help to a degree. We have set up operational parameters to allow us run run at elevated stacks (up to 6 panels/spindle), but as a result we are generating impacted debris at the plunge points that our current board washing system (uses plain heated water only) cannot remove. Particularly troublesome is a ring of melted fiberglass debris that is created on the board surface and sticks to the solder mask. Any suggestions on chemical additives for our cleaning systems, alternative cleaning methods, or methods to reduce generation of the defect would be greatly appreciated.

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Earl Moon

#15748

Re: Cleaning PCB's after routing | 24 May, 1998

| Hello, | I am looking for suggestions for cleaning pcb's after the routing (fabrication) process. Keep in mind that these pcb do not have components intalled on them yet. | We have considered pre-drilling the routing plunge points, but cost and capacity concerns do not make this an option. Lowering plunge parameters and alternative routing cutter styles only help to a degree. We have set up operational parameters to allow us run run at elevated stacks (up to 6 panels/spindle), but as a result we are generating impacted debris at the plunge points that our current board washing system (uses plain heated water only) cannot | remove. Particularly troublesome is a ring of melted fiberglass debris that is created on the board surface and sticks to the solder mask. | Any suggestions on chemical additives for our cleaning systems, alternative cleaning methods, or methods to reduce generation of the defect would be greatly appreciated. I must assume you are a pcb fabricator. Therefore, as I have been in this business for some time, I have never cleaned boards for the reason you describe. No criticism intended, but the only reason I have ever cleaned bare fabs is to meet normal and ionic cleanliness requirements. The melted "fiber glass" is, obviously epoxy resin that cannot be cleaned as you wish but can be prevented. I don't understand why you cannot either establish router start points as part of your tooling hole drilling operation. If, as you say, this is not cost effective, can't you start at the panel's edges and enter the route process from their? Failing this, I can only say that epoxy smear is caused by the wrong feeds and speeds. That is: If a router tool is not sharp and is introduced to the material to be routed at too high a speed or movement along a path (just as in drilling holes), excessive smear is effected. I recognize your problem, but I believe it must be prevented instead of being washed away. Wish you well, Earl Moon

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David Newman

#15749

Re: Cleaning PCB's after routing | 4 June, 1998

| I must assume you are a pcb fabricator. Therefore, as I have been in this business for some time, I have never cleaned boards for the reason you describe. No criticism intended, but the only reason I have ever cleaned bare fabs is to meet normal and ionic cleanliness requirements. | The melted "fiber glass" is, obviously epoxy resin that cannot be cleaned as you wish but can be prevented. I don't understand why you cannot either establish router start points as part of your tooling hole drilling operation. If, as you say, this is not cost effective, can't you start at the panel's edges and enter the route process from their? Failing this, I can only say that epoxy smear is caused by the wrong feeds and speeds. That is: If a router tool is not sharp and is introduced to the material to be routed at too high a speed or movement along a path (just as in drilling holes), excessive smear is effected. | I recognize your problem, but I believe it must be prevented instead of being washed away. | Wish you well, | Earl Moon We are a high volume pcb fabricator, where most of the boards we make require complex profiling with numerous internal cuts. As such, to add "router start-points" would require adding in some cases over 1,000 holes to the drilling operation / drilling stack -- a costly proposition. When cutting outlines, this entry-point defect is not a problem. It is primarily troublesome in complex internal features and short routed slots. To clarify the problem a bit, what I am dealing with is in fact not epoxy smear, as you suggested but rather caking of the router dust in the interstitial spaces between the stack of panels. This caked dust tends to stick to the board (perhaps due to a slight melting- although I have observed little to no damage to the solder mask at the entry points, as is characteristic when I do encounter smear.) Below I will list the measures I have taken to reduce/eliminate this problem. 1. Reduce the pressing force in the floating presssure foot. This problem is most pervasive (ironically) on our new Hitachi Routers with a floating pressure foot. I found excessive pressure inhibits air-flow between panels, and is a primary cause of the problem. 2. Drillpoint router bits. I have found the alternate tip geometry to be effective with 3/32" --> 1/8" cutters, although they can only be used with our newer height-controlled machines. 3. Reduction of operating parameters. Reduced Z-axis plunge rates for the larger cutter sizes. 4. Addition of a 1/2 sec. dwell at the plunges. The small pause helps to loosen the impacted debris and caked debris, so that it will flake off easier 5. Replaced backup material with "corrugated plastic" which has long air channels to increase air flow through the panels. Big cost savings too!! 6. Modifications to the washing systems- looking at dry bursing, agitation, air knives, and higher pressure washers. And still looking for more! Thanks, Dave

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Earl Moon

#15750

Re: Cleaning PCB's after routing | 9 June, 1998

| | I must assume you are a pcb fabricator. Therefore, as I have been in this business for some time, I have never cleaned boards for the reason you describe. No criticism intended, but the only reason I have ever cleaned bare fabs is to meet normal and ionic cleanliness requirements. | | The melted "fiber glass" is, obviously epoxy resin that cannot be cleaned as you wish but can be prevented. I don't understand why you cannot either establish router start points as part of your tooling hole drilling operation. If, as you say, this is not cost effective, can't you start at the panel's edges and enter the route process from their? Failing this, I can only say that epoxy smear is caused by the wrong feeds and speeds. That is: If a router tool is not sharp and is introduced to the material to be routed at too high a speed or movement along a path (just as in drilling holes), excessive smear is effected. | | I recognize your problem, but I believe it must be prevented instead of being washed away. | | Wish you well, | | Earl Moon | We are a high volume pcb fabricator, where most of the boards we make require | complex profiling with numerous internal cuts. As such, to add "router start-points" | would require adding in some cases over 1,000 holes | to the drilling operation / drilling stack -- a costly proposition. | When cutting outlines, this entry-point defect is not a problem. | It is primarily troublesome in complex internal features and | short routed slots. | To clarify the problem a bit, what I am dealing with is in fact not | epoxy smear, as you suggested but rather caking | of the router dust in the interstitial spaces between the stack of panels. | This caked dust tends to stick to the board (perhaps due to a slight | melting- although I have observed little to no damage to the solder | mask at the entry points, as is characteristic when I do encounter smear.) | Below I will list the measures I have taken to reduce/eliminate this problem. | 1. Reduce the pressing force in the floating presssure foot. This problem | is most pervasive (ironically) on our new Hitachi Routers with a floating | pressure foot. I found excessive pressure inhibits air-flow between | panels, and is a primary cause of the problem. | 2. Drillpoint router bits. I have found the alternate tip geometry | to be effective with 3/32" --> 1/8" cutters, although they can only be used | with our newer height-controlled machines. | 3. Reduction of operating parameters. Reduced Z-axis plunge rates for the | larger cutter sizes. | 4. Addition of a 1/2 sec. dwell at the plunges. The small pause helps to | loosen the impacted debris and caked debris, so that it will flake off | easier | 5. Replaced backup material with "corrugated plastic" which has long | air channels to increase air flow through the panels. Big cost savings | too!! | 6. Modifications to the washing systems- looking at dry bursing, | agitation, air knives, and higher pressure washers. | And still looking for more! | Thanks, | Dave You guys do know what you're doing. Have you tried ultrasonic cleaning? Earl

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