Info on OSP PCB�s

I've had good and bad experiences with OSP's. First of all, ask yourself, "Why use an OSP?" If you don't need it, don't use it. Solderability is dependent upon the number of thermal passes (the fewer, the better), the thickness of the coating, the type of flux, and exposure of the PCB's to the ambient. I've had the stuff not solder with a very agressive organic acid before due to coating thickness and also due to degredation of coating caused by crappy storage and handling. Make sure whomever your supplier is uses some sort of process control regarding coating thickness. If they don't have a photospectrometer or other type of measurement device for film thickness analysis, DO NOT USE THEM. That's the best advice I can give you. There are a million suppliers who offer the capability but your best bet is to find one with a good customer base, good controls, uses Entek Plus (That's my favorite coating), and has lots of experience processing OSP coated boards. Shelf life is about 6 months to a year depending on the material and the ambient conditions of your storeroom. There are many types of OSP's. Protecto, Imidizole, Surecoat, and Entek are just a few of them. Imidazole is Via Systems proprietary coating though I think they license it out. It's alright. I don't like Surecoat at all. Don't use Entek unless it's the Cu-106A. I've never used Protecto. I'm sure Dave F (That's F for "Freakin'Smart" by the way) can offer up a lot more info. Shoot him an e-mail. He's all over this forum and he's pretty cool to talk to. He seems to know every facility in the country related to every process available so he may have some advice on some good shops to use...

Good luck, justin

reply »

You aren't going to post our stuff on your "Hey, I'm the wizard site", are you?

Board fab, Pad coatings, OSP

1 OSPs: Imidazole (Via Systems) is good. Entek (Enthone) works, but requires strict thickness control in fab.

2 Enthone CU56 allows one thermal cycle. CU106A allows three thermal cycles.

3 Entek Plus CU-106A. Yes, just about everything removes Entek, especially if there's heat involved. Ethone states: 3a Alcohol strips 70% of the coating 3b Water removes 15% 3c Kyzen Lonox only takes about 3%. 3d Enthone recommends that if you wash the board "thoroughly" (alcohol or solvent) strip the coating and expose copper, you complete all soldering operations within 12 hours.

4 Enthone-OMI specifies thickness range is to be 0.2 to 0.5 um (7.87 to 19.7 uinch) for ENTEK Plus CU-106A. Nominal should actually be 0.35 to 0.40um (13.7 to 15.7 uinch). Our fab runs fairly tight at 0.38 to 0.42um (14.9 to 16.5 uinch). [I know I'm probably making a mistake, doing these unit conversions, and Genny is going to bustin' me, but hey, I continue to live on the wild (dumb) side, eh?]

5 A silver nitrate test doesn't actually "check thickness". It is a tool that can be used to verify the presence and integrity of the coating. Silver nitrate of a known normality(0.01-0.10N) is placed by dropper on the board and held for a given time [10-60sec]. This is rinsed dried and inspected. A discolored or darkened appearance of the copper MAY indicate an insufficient coating. 5a There isn't any one acceptable thickness, it really depends on the type of OSP being used and your assembly process and chemistries. If possible work with the PCB supplier and their OSP vendor. They should be able to give you a starting point to test from. Then determine what thickness works best for your application. 5b Assuming your PCB supplier has the capability to do quantitative thickness testing (typically I.R. or U.V.) you can establish an acceptable thickness range with them. 5c Since the formation of the OSP coating thickness is pretty much self limiting, thin coating will probably be more of a concern. By empirically testing boards below and within the specification with silver nitrate at a given normality and time you could arrive at a spot test for coating integrity. 5d If possible, the best test is running an unpopulated PCB through your processes.

6 Shelf life: [months] Entek CU-56: 6 Entek Plus CU-106: 12

7 I hate this crap!!! Those little GD copper borders drive me buggy, regardless if they're "acceptable" er not. Oooo, did the fab put the crap on too thin? Oooo, did the fab put the crap on too thick? Well, we'll find-out, rite soon.

reply »