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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Finishing myth ?

JoSi

#15921

Finishing myth ? | 13 May, 1998

Hi, There has been a lot of disputes in our company about changing present HASL to another Finishing which can provide more flatter pad surface in fine pitch applications. ( perhaps Ni/Au, OSP ) The target is to reduce solder defects, thus improve quality and on the other hand reduce rework. Does anyone know any reliable study etc to back up this theory, or is it only a myth created by clever salesmen. ? Brs, JoSi

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Justin Medernach

#15923

Re: Finishing myth ? | 15 May, 1998

| Hi, | There has been a lot of disputes in our company | about changing present HASL to another Finishing | which can provide more flatter pad surface in fine | pitch applications. ( perhaps Ni/Au, OSP ) | The target is to reduce solder defects, thus improve | quality and on the other hand reduce rework. | Does anyone know any reliable study etc to back up | this theory, or is it only a myth created by clever | salesmen. ? | Brs, JoSi JoSi, Give me a call. We'll chat about pros and cons and what really happens. I don't want to arouse any lurking salesmen in the PCB industry. 978 392 3218 (eastern std. time) Justin

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Earl Moon

#15922

Re: Finishing myth ? | 15 May, 1998

| Hi, | There has been a lot of disputes in our company | about changing present HASL to another Finishing | which can provide more flatter pad surface in fine | pitch applications. ( perhaps Ni/Au, OSP ) | The target is to reduce solder defects, thus improve | quality and on the other hand reduce rework. | Does anyone know any reliable study etc to back up | this theory, or is it only a myth created by clever | salesmen. ? | Brs, JoSi

Salesmen and myths? How could they mislead. I've been so trusting and now it's over. Actually, HASL sucks (not trying to be offensive and offend proponent's sensibilities) not only because it is not flat, but because it often is not solderable. I wrote a "terriffic" (self declared) article (December 1992, I think, issue of Printed Circuit Fabrication Magazine) about all the problems associated with HASL. In it, as I remember - not having a copy anymore to rebuild my diminishing ego, I discussed not only topographical problems but those associated with SMT solderability as uncontrollable processes in the fab shops. Anyway, no matter the sales pitch, almost anything is better than HASL'd board solder termination areas. Immersion gold over nickel (when properly coated) is quite good. So are organic coatings though shelf life is a major issue. Palladium works with work. Silver works well when processes are managed effectively. Tin/Lead plating is still the best but it must be reflowed. Tin immersion, except with some exceptions (I've seen none) is supposed to be good but look out for shelf life problems as excessive oxide to surface metal ratios. It's simple - get solderable surface coatings and enjoy wetting as never before as well as having a flat surface on which to mount. Earl Moon

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Reflow Ovens thermal process improvement