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Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Accidental solder mask

Tim Marc

#22759

Accidental solder mask | 17 December, 2002

Hello all,

One of our PCB manufacturers coated a through hole connecters vias with solder mask. The only IPC references that comes close to describing this problem is 2.9.2 Registration to holes, and subsequent specification 6.3.1 PTH � Vertical fill of hoes. The connector is a 72P M .39 STACK H DU ROW .05X.10. Given its size, and the mask problem it�s a bit tough to solder. There will be no fillet, however if we achieve 75% fill of the via will it pass IPC class two?

Thanks,

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RDR

#22760

Accidental solder mask | 17 December, 2002

You looked one page to far in the IPC book! Fillet height of 75% is acceptable for all 3 classes.

Per IPC 610 rev. C Section 6 table 6.2.

A. Circumferential wetting on Primary side (top)between lead and barrel (not anualar ring) Class 1 Not spec'd Class 2 180 Deg. Class 3 270 Deg.

B. verticle fill of solder Class 1 Not spec'd Class 2, 3 75%

C. Circumferental fillet and wetting on secondary (bottom) of lead and barrel Class 1,2 270 Deg. Class 3 330 Deg.

D. Percentage of land (anular ring)covered with wetted solder on Primary side Class 1,2,3 0%

E. Percentage of land covered on secondary side Class 1,2,3 75%

So as you can see you have met (D) with 0% solder coverage on the land. You will meet (B) with 75% verticle fill. So you need to make sure that A,C,and E are met. (180 deg wetting in the barrel at the top, 270 Deg. wetting on bottom pad, and at least 75% of the anular ring wetted on the bottom.

Hope this helped

Russ

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#22762

Accidental solder mask | 17 December, 2002

I�m not clear on the problem.

What I get: * Your fabricator did not deliver the product that you asked for in your purchase order. * Pad. Land. A portion of a conductive pattern used as a termination area. Metal surrounding a hole on a printed circuit board. * Plated-Through-Hole (PTH). A plated-through hole is one formed by a deposition of metal on the inside surface of a through-hole. Also known as a supported hole. The configuration is used to provide additional mechanical strength to the soldered termination or to provide an electrical interconnection on a multilayer printed circuit board. * Via. A plated-through-hole used as a through connection between layers on the printed circuit board. Vias are not intended to be used for component lead insertion.

There is no IPC requirement for via filling. In fact, unfilled via are more reliable than filled or partially filled via. So, here�s what I don�t get: * Do your internal, company requirements indicate a need for via fill? * You say, �The connector is a 72P M .39 STACK H DU ROW .05X.10. Given its size, and the mask problem it�s a bit tough to solder.� What does this mean? And what does this have to do with solder mask coated via? What does this have to do with via fill?

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Tim Marc

#22764

Accidental solder mask | 17 December, 2002

Thanks Russ. You were right I looked one page too far. We can meet (A,B,C,D). To meet the 75% of (E) the annular ring will have to be scraped. Your help was much appreciated.

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Tim Marc

#22765

Accidental solder mask | 17 December, 2002

Dave, I�m talking about the 75% vertical fill of solder IPC 6.3 criteria (B), and 6.3.1 Fig 6-5. I also referred to the annular ring of the Plated-Through-Hole, being coated with solder mask. Semantics, yes I did refer to the Plated-Through-Hole (Supported) as a "via", with respect to that being used in conjunction with the connector. Thanks, I have my answer, IPC 6.3 criteria (E) = 75%. I sincerely appreciate your reply, and knowledgeable input.

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#22773

Accidental solder mask | 18 December, 2002

Thanks Tim. Additional thoughts are: * We've talked here on SMTnet about hole fill previously. * That your ability to get hole fill is probably limited by mask in the hole makes us very uneasy, because hole could have varying levels of solder mask in them.

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RDR

#22774

Accidental solder mask | 18 December, 2002

Dave, You stated that an unfilled via is of greater strength than a filled or partially filled via. I posted to another thread recently and I stated that a filled via was of greater strength than an unfilled. I was tought (incorrectly?) that a filled via was much less prone to "knee breaks" since the solder enhanced the connection? I am curious as to if I was incorrectly informed, new studies are showing different?, etc... Thanks for any info you could provide on this. Is it located in a book in Daves bookshelf?

Russ

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#22775

Accidental solder mask | 18 December, 2002

No, sorry not on "Dave's Bookshelf". My basis is a study done at IBM. I reference it here: http://www.smtnet.com//forums/index.cfm?fuseaction=view_thread&CFApp=1&Thread_ID=4941&#Message19050

Responding differently, you're correct. If you have a POS via that is going to knee crack, sure filling it with solder probably IS better than not. But for just regular plated holes nothing is better. Agreed, it's a little counterintuitive initially. But when you think about all those different materials sandwiched together and expanding and contractiing at different rates during heating / cooling cycles, you get to think that maybe you'll pass on hole fill.

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RDR

#22779

Accidental solder mask | 18 December, 2002

Thanks Dave

Russ

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