Thanks Chris.
I passed this on to my colleague (not my company's work).
Bob
-----Original Message-----
From: Chris Mahanna [mailto:[log in to unmask]]
Sent: Tuesday, November 16, 2010 9:52 PM
To: 'Bob Landman'; [log in to unmask]
Subject: RE: [TN] the reliability of capped vias in pads
Bob,
Sorry for the delay. From the pictures, it appears that you smoked the resin around the microvia.
Which means that you tortured the via.
If you used a direct heat (smartheat) iron, I'd guess you used a 700 or 800 series. 500 series should work for SnPb, 600 for Pb-free.
If the picture is deceiving me about the resin loss, it could be that you have a subpar plating interface at the bottom of the via. Root cause can be any of the making hole conductive processes.
BTW-your via appears to not be filled with copper, but rather a separate fill process.
Beyond that, I would suggest standardized structural integrity testing on microvias, prior to your DOE for rework.
Chris
Chris Mahanna
Robisan Laboratory
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bob Landman
Sent: Thursday, November 11, 2010 5:26 PM
To: [log in to unmask]
Subject: Re: [TN] the reliability of capped vias in pads
Thanks Chris.
Just sent pictures to Steve G to post.
Here are some additional comments from my colleague on the problem he's confronting:
1. there are two types of capped vias:
a. through hole vias filled with conductive polymer and
b. laser drilled microvias "filled" with copper (the copper is electroplated in a special formulated copper electrolytic solution that selectively plate copper in the vias (the copper plate rate in the vias is 3 to 4 time higher than on the PCB panel)
In both types the via is capped with electroplated copper. The copper thickness is about the same as the copper conductors on the CS or PS , that is 50 - 70 micron ( 2- 3 mils).
In both types there are some reliabilities problems.
He's asking about the second type of vias.
Removing a soldered lead component from a capped (microvias) pad may apply a pull force on the vias under this pad and aided by the heating of the region by the touch of the solder iron can seperate the microvia from the capture pad.(i.e the second layer that is under the outer CS or PS layer, see the photos in the attached file (in the photos the laser microvias are not capped).
He needs information about failures of boards with capped microvia from people that allow hand soldering repair.
Thanks!
Bob Landman
H&L Instruments, LLC
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Chris Mahanna
Sent: Wednesday, November 10, 2010 9:54 PM
To: [log in to unmask]
Subject: Re: [TN] the reliability of capped vias in pads
The 6012C cap requirements are intended to assure a minimal structural feature. As such, IMO wrap continues to be the most important reliability feature.
If your fabs are laying down 2-4 mil caps that's a different story.
Chris
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Frank Kimmey
Sent: Tuesday, November 09, 2010 10:33 PM
To: [log in to unmask]
Subject: Re: [TN] the reliability of capped vias in pads
Bob,
I don't know I can give definitive proof of but I am pretty sure (good Engineering reference) capped via in pad can be considerably more reliable in manual rework than standard pad. With the additional copper going through the board it should give considerably better resistance against thermal caused pad lift (more surface area to adhere to board, plus pads on both sides). I would always be more comfortable hand soldering through hole than SMT. Due to the mechanical definitions of a capped via I would expect through hole soldering rules may apply better than surface mount. As to your specific questions, I think those all must be determined internally depending on your available skill levels and reliability needs.
Sorry I don't have better, maybe Werner will take a break from golf to answer.
Hope it helps some,
FNK
Frank N Kimmey CID+
Manager - PCB Design
Powerwave Technologies Inc
Mobile - 916-670-0645
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bob Landman
Sent: Tuesday, November 09, 2010 10:50 AM
To: [log in to unmask]
Subject: [TN] the reliability of capped vias in pads
A colleague asked me for information about the reliability of capped vias in pads:
1) How many allowed repairs?
2) Is it acceptable to hand solder wire lead components on those pads?
3) How many allowed repairs are allowed for hand soldered component leads on thes pads?
4) What is the recommended soldering iron tip temperature? (for lead-free and tin/lead solders)
5) Is the solder tip "touch up" time controlled well enough by the average repair technican when done manually to be acceptable or is only reflow soldering recommended (no rework)?
6) Is the touch up time more variable, longer, when the solder is Lead Free? (I would say yes it is and we only use eutectic tin/lead solder on COTS lead-free boards when we do a repair)
7) Are there any restrictions on placing a via in a pad if the component leads are hand soldered to this pad?
Bob Landman
H&L Instruments, LLC
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