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August 2012

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From:
"Gervascio, Thomas L" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Gervascio, Thomas L
Date:
Wed, 8 Aug 2012 11:18:42 +0000
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We had pretty good luck with a pin and paste process using solder paste (instead of tacky flux) and solder performs (30 mils x 60 mils x 30 mils). Because of the dimensions on the connector leads versus the plated through hole dimension we couldn't get enough solder paste to get 75% PTH fill. The solder perform contributed about 85% of the final solder joint volume. We wound up using a Camalot to dispense just enough paste. We also found that using a tacky flux paste gave us more voiding in the final solder joint than solder paste. I thought it might be related to the solder profile - are using a ramp-soak-spike profile. The only unique about the process is that we have to place (two) 0603 solder performs on the opposite side of the PTH hole due to real estate limitations. We used solder performs from Indium on tape and reel (machine placed them) but Kester and Alpha et al make the performs.

Tom


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Tuesday, August 07, 2012 6:18 PM
To: [log in to unmask]
Subject: EXTERNAL: Re: [TN] pin in paste

Yes, it did work quite well. We simply stuck the grid-pattern pre-forms onto the connector pins with tacky flux on them to hold them to the bottom of the connector, then manually placed the connector so the pre-forms were between the connector and the PWB. During reflow the solder melted and the connectors dropped down on the board about 99.5% of the time, with no issues. Once in a great big while we would get one where the connector did not drop down flush, but then we found that if we added the mounting hardware and snugged them up, they dropped down flush 100% of the time. 
We never saw any bridges under the connector like we feared we would, not a one. That was very surprising. It was a big cost savings not to have to selectively solder the connector in afterwards. However, this does not work for every connector/board design, you need to develop the process and see what works and what doesn't. It takes a good X-ray to make sure the SJs are acceptable.
The other thing I found surprising was that connectors and components with L-shaped leads were much easier to do this with, than are radial-leaded connectors where the leads came straight down from the body, as long as the pre-forms were down on the top of the PWB. In this case I brushed the tacky flux onto the PWB in the area of the connector pins, placed the pre-form on the right angle leads, then placed the connector and made sure the pre-form was down on the connector holes prior to reflow. The tacky flux on the surface of the assembly held the pre-form down during reflow, and the solder filled all the holes just right. However, for whatever reason, more bridges formed between the SJs of the right angle leaded parts, although not in any great numbers. 
Oh, yeah, I almost forgot. It takes a good operator, because the pin patterns are usually synchronous. They can actually place the pre-form on the connector off one pin, or 2, or an entire row if there is more than one row. I tried to make an alignment fixture that had a nest for the pre-form pattern, brushed the tacky flux on the connector pins, then placed it in the raised contour to align it to the pre-form. This worked for about 12 connectors in a row on average before the fixture needed to be washed of tacky flux, so we threw that idea out the window and just found one operator who could be depended on to get it right every time. I am sure there are ways to improve this process. 
Not sure about the others, but Kester makes pre-forms in just about any pattern, shape, and size you could wish, and they are not expensive.

-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Tuesday, August 07, 2012 4:22 PM
To: TechNet E-Mail Forum; Stadem, Richard D.
Subject: RE: [TN] pin in paste

I used to do a lot of pin in paste on connectors but it has been long enough that I cannot remember if I eliminated the voiding completely or not.  My memory says that I achieved the 75% and did not have
unacceptable voiding.   I remember the worst part of PIP was the dragout
problem of inserting the pins through the solder paste and dripping on the placement equipment.  Don't have an documents to refer you to offhand.  Dean's honeycomb pre-forms sounds like a proven method albeit more costly.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Tuesday, August 07, 2012 2:16 PM
To: [log in to unmask]
Subject: Re: [TN] pin in paste

Hi, Joyce.
Sorry, I tried different methods using paste and different brands of paste (including pre-drying) on connector pins but could not escape the voids entirely. Pre-drying the paste after insertion/before reflow did reduce the voiding, but was not practical from an assembly standpoint. I ended up using honeycomb (daisychain) pre-forms, with absolutely no voiding but a few minutes of added assembly time. If anyone else has ideas, I also would like to hear about them.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo
Sent: Tuesday, August 07, 2012 4:04 PM
To: [log in to unmask]
Subject: [TN] pin in paste

Joyce Koo
Materials Researcher - Materials Interconnect Lab Research In Motion Limited
Office: (519) 888-7465 79945
Mobile: (226) 220-4760

Hi, Calling on all of the gurus, Anyone has one or two good reference regarding voiding minimization or voiding elimination for pin in paste?
Hopefully it is not in need of using performs.  Many thanks for all your help. 
Best regards,
            joyce

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