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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Murray Pulman

#11725

Specifying Pcb Format/Construction. Help!! | 26 April, 1999

Help Guys!!

We sub con assemble small to medium batch runs of mixed tech boards inc fine pitch BGA o4o2 etc.

As usual we get all the crap to build that no-one else wants, however lately some customers are getting a little more serious with their sales & marketing and things are beginning to move .

My problem is advising them on board technology to achieve consistancy etc.

At present everything is HASL but the results vary enourmously, and as a result we have problems from batch to batch with placing the fine pitch devices 0402 etc.

I need everyones opipion on the board spec to recommend. The finished products are worth serious money but a sense of commercial reality must be maintained!!. All I get from the board manufacturer is bullshit, I need some practical advise from end users.

As i am sure you can guess we have grown into this position over 4-5 years and do not have the technical skills in house to spend months working on this, but things must get better PDQ or we will be losing our customers confidence.

Help!!

Regards

Murray.

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Justin Medernach

#11726

Re: Specifying Pcb Format/Construction. Help!! | 26 April, 1999

| Help Guys!! | | We sub con assemble small to medium batch runs of mixed tech boards inc fine pitch BGA o4o2 etc. | | As usual we get all the crap to build that no-one else wants, however lately some customers are getting a little more serious with their sales & marketing and things are beginning to move . | | My problem is advising them on board technology to achieve consistancy etc. | | At present everything is HASL but the results vary enourmously, and as a result we have problems from batch to batch with placing the fine pitch devices 0402 etc. | | I need everyones opipion on the board spec to recommend. The finished products are worth serious money but a sense of commercial reality must be maintained!!. All I get from the board manufacturer is bullshit, I need some practical advise from end users. | | As i am sure you can guess we have grown into this position over 4-5 years and do not have the technical skills in house to spend months working on this, but things must get better PDQ or we will be losing our customers confidence. | | Help!! | | Regards | | Murray. | Hi Murray, Your predicament isn't as bizarre as you would think and you're certainly not in a position to have to worry about economic issues concerning board cost. As a rule, you shouldn't use a HASL PCB when populating 0402, UBGA, CSP, etc. Those should always have an alternative surface finish. I have product with .016" pitch and I have a HASL substrate. It works great. Why??? The features on the board, even the .016" device, don't exhibit a tendency to puddle or breadloaf. In other words, the features are large enough to accomodate a HASL process. Smaller features, such as micro BGA pads and 0402 pads, hold onto the solder and don't blow off well in a HASL process. This is where white tin, gold, OSP all come into play. If your board mfr. says they cost more, he's full of it. You can definitely find alternative finishes with costs comparable to HASL. Also, if you're seeing that much lot to lot difference on your boards, part of the ownership belongs to you. You need to spec to your board mfr that you want no more than 1 mil of HASL on the pads etc. Go in to his shop and sniff around. Find out what they do for a process that would yeild such variability. Good HASL houses are hard to find in a world where there seems to be a "bucket" PCB shop on every corner. In general, if you have 0402 or fine pitch BGA devices (CSP too) advise that the customer consider an alternate surface finish in order to eliminate the coplanarity variable.

Regards, Justin

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#11727

Re: Specifying Pcb Format/Construction. Help!! | 26 April, 1999

Hi Murray!

Justin pretty much summed things up...covered all the points. So I'm just gonna give you my preference of what I like other than HASL finish.

Electroless Nickle/Immersion Gold...nice flat pads...hmmmmmmm, Steve likes flat pads. OSP's have the little problems of what to do with mis-prints and whatnot, and with the Tin finishes there's still the debate going on about reliabilty from more than just a few people.

We've all been soldering to gold for quite a while, and just about have all the issues taken care of. Don't put too much gold on the pads and you're fine. Plus, it gives the PCB's that classy "Tiffany's" look....(GRIN)

Justin is right about cost, it should be equal to the cost of HASL or maybe just a teeny-weeny bit higher, not much though. If it is a bit more, it'll pay for itself in the reduced defects that you'll have with fine pitch and/or CSP assembly.

Justin also brought-up a good point about becoming good bud's with the fab shop...well maybe not bud's, but do go and sniff around to make sure they're capable and doing things in the way that makes you feel comfortable. You know a lotta times the best way to find a good fab shop is simply word of mouth. Anybody can put on a good "dog and pony" show, but it means something when you talk to others that's in the same position you are and they recommend shops to ya.

-Steve Gregory-

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John W

#11728

Re: Specifying Pcb Format/Construction. Help!! | 26 April, 1999

| Hi Murray! | | Justin pretty much summed things up...covered all the points. So I'm just gonna give you my preference of what I like other than HASL finish. | | Electroless Nickle/Immersion Gold...nice flat pads...hmmmmmmm, Steve likes flat pads. OSP's have the little problems of what to do with mis-prints and whatnot, and with the Tin finishes there's still the debate going on about reliabilty from more than just a few people. | | We've all been soldering to gold for quite a while, and just about have all the issues taken care of. Don't put too much gold on the pads and you're fine. Plus, it gives the PCB's that classy "Tiffany's" look....(GRIN) | | Justin is right about cost, it should be equal to the cost of HASL or maybe just a teeny-weeny bit higher, not much though. If it is a bit more, it'll pay for itself in the reduced defects that you'll have with fine pitch and/or CSP assembly. | | Justin also brought-up a good point about becoming good bud's with the fab shop...well maybe not bud's, but do go and sniff around to make sure they're capable and doing things in the way that makes you feel comfortable. You know a lotta times the best way to find a good fab shop is simply word of mouth. Anybody can put on a good "dog and pony" show, but it means something when you talk to others that's in the same position you are and they recommend shops to ya. | | -Steve Gregory-

Well as usual Justin & Steve have got the story covered, only other point is that u may want to investigate using a 2% silver solder when u move to the gold finish it removes any danger of the gold migrating into the joint either during the manufacture or later in life I did a 'visit' to a fab house we were having trouble with and got lot's of stuff sorted out, if nothing else it let's u appreciate what they r doing, it can be an eye opener.

good luck

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Murray Pulman

#11729

Thankyou | 27 April, 1999

Charles Stringer

#11730

Re: Specifying Pcb Format/Construction. Help!! | 27 April, 1999

| Hi Murray! | | Justin pretty much summed things up...covered all the points. So I'm just gonna give you my preference of what I like other than HASL finish. | | Electroless Nickle/Immersion Gold...nice flat pads...hmmmmmmm, Steve likes flat pads. OSP's have the little problems of what to do with mis-prints and whatnot, and with the Tin finishes there's still the debate going on about reliabilty from more than just a few people. | | We've all been soldering to gold for quite a while, and just about have all the issues taken care of. Don't put too much gold on the pads and you're fine. Plus, it gives the PCB's that classy "Tiffany's" look....(GRIN) | | Justin is right about cost, it should be equal to the cost of HASL or maybe just a teeny-weeny bit higher, not much though. If it is a bit more, it'll pay for itself in the reduced defects that you'll have with fine pitch and/or CSP assembly. | | Justin also brought-up a good point about becoming good bud's with the fab shop...well maybe not bud's, but do go and sniff around to make sure they're capable and doing things in the way that makes you feel comfortable. You know a lotta times the best way to find a good fab shop is simply word of mouth. Anybody can put on a good "dog and pony" show, but it means something when you talk to others that's in the same position you are and they recommend shops to ya. | | -Steve Gregory- | Murray Just my ten pence worth from the UK..... Watch the solderability of your through hole components - if any when using gold over nickel. Sometimes the wetting is not all you would like it to be especially when you look at the top side of the board.

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