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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Bare Copper Circuit Boards

C.K.

#10939

Bare Copper Circuit Boards | 18 June, 1999

Has there anyone bold enough to try this in their shops? My cubemate just got through telling me that at his last shop, they had bare copper boards (no HASL, no OSP, no nothing), with minimal solderability problems.

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John Thorup

#10940

Re: Bare Copper Circuit Boards | 18 June, 1999

| Has there anyone bold enough to try this in their shops? My cubemate just got through telling me that at his last shop, they had bare copper boards (no HASL, no OSP, no nothing), with minimal solderability problems.

I'd hate to have to clean whatever kind of flux they were using. Maybe battery acid? Possibly there was an OSP present without his knowledge. Possibly witchcraft? John Thorup

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Dean

#10941

Re: Bare Copper Circuit Boards | 18 June, 1999

| Has there anyone bold enough to try this in their shops? My cubemate just got through telling me that at his last shop, they had bare copper boards (no HASL, no OSP, no nothing), with minimal solderability problems. | yes, 8 years ago I developed mfg. processes around a product which used no surface finish (copper only). The product was very cost sensitive so the customer decided to cut costs wherever possible. Keep in mind it was very simple (about 30 parts per sq. inch.) All parts were passives with two IC's (soic 8 / 16). I chose RMA rosin soler paste with a fairly high activity level. The biggest problem was solder thieving as there was no solder resist to define and limit thieving. But keep in mind as a low cost product if there was ANY evidence of wetting it was shippable (consumer grade specs). I should also point out the fabs went through a fab scrubber prior to solder print and was cleaned in Prelete (freon) prior to conformal coating. Back then you could clean and degrease anything with prelete. We did about 500,000 units and had the same failure rates as processes using hasl. This type of process was only successful because of low quality standards set by the customer. (these were disposable radio ID tags (RFID) for farm animals. Moo. It was an interesting experience, but I have not seen or heard of since. Dean

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#10942

Re: Bare Copper Circuit Boards | 20 June, 1999

| Has there anyone bold enough to try this in their shops? My cubemate just got through telling me that at his last shop, they had bare copper boards (no HASL, no OSP, no nothing), with minimal solderability problems. | Is your cubemate the same guy who told me I could drive from Houston to New Orleans in three hours, 'cause he does it all the time? Or the one who says he shoots in the low 80's but can't par a hole to save his lif when you finally get out on the golf course? Smells like a little "embellishment" going on here.

I did have boards with a copper finish and no OSP. The only thing protecting the copper from oxidation was the Cu-chromate layer on the foil. These are the puppies that I frequently have referred to as the "bitch boards." The ones that only the Alpha 310B flux could solder. The ones used in our reduced purity nitrogen trials that caused defect to triple when the nitrogen feed in the wave was reduced from near 100% purity to 97% purity. The ones that exemplify that fine line between cost-effective and totally unusable (s)crap.

I guess it comes down to what you define as "minimal" solder problems. Then there's the school of thought that if you don't see the defect, and don't record the defect, then it's really not a defect, right? (No offense to your cubemate; I'm referring to a shop that I once worked in.)

So yeah, you can, under the right conditions, skip the protectant, but I think it would be highly unadvisable. If it were a realistic process, some big guys in highly competitive markets (like the Motorolas or Compaqs of the world) would be doing it and publishing papers about the great benefits of it.

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