Thanks, Graham, good to know. I was afraid it might be PTH transistors, and you would end up with latent reliability issues.
From: Graham Collins [mailto:[log in to unmask]]
Sent: Tuesday, September 04, 2018 8:00 AM
To: Stadem, Richard D; Tan Geok Ang; [log in to unmask]
Cc: [log in to unmask]
Subject: Re: [TN] qualifying a heatsink attach process
SMT parts, rated for lead free but to be used in a leaded process in this instance. I'm not worried about the part survivability.
Graham Collins
Senior Process Engineer
Sunsel Systems
(902) 444-7867
On 9/4/2018 9:43 AM, Stadem, Richard D wrote:
The concern is not the TYPE of REFLOW process, but whether or not the (assumed) TO-5 transistors will survive a reflow process. I am assuming they are through-hole parts never intended to go through any reflow process where the entire CCA reaches reflow temperatures. The internal transistor temperature seen from a reflow process whether convection or vps is much hotter than the internal component temperature seen from wave, select, or hand solder process.
From: Tan Geok Ang [mailto:[log in to unmask]]
Sent: Friday, August 31, 2018 10:10 PM
To: TechNet E-Mail Forum; Stadem, Richard D; [log in to unmask]<mailto:[log in to unmask]>
Subject: Re: [TN] qualifying a heatsink attach process
Believe it can be a single process by using vapour phrase reflow with vacuum process
________________________________
From: Stadem, Richard D <[log in to unmask]><mailto:[log in to unmask]>
Date: 31 August 2018 at 3:22:52 AM SGT
To: [log in to unmask]<mailto:[log in to unmask]> <[log in to unmask]><mailto:[log in to unmask]>
Subject: Re: [TN] qualifying a heatsink attach process
Good point, Joyce. And while the flatpack will go through reflow, Graham will need to make sure the transistor can also, from a max. temperature standpoint.
-----Original Message-----
From: Yuan-chia Joyce Koo [mailto:[log in to unmask]]
Sent: Thursday, August 30, 2018 2:02 PM
To: TechNet E-Mail Forum; Stadem, Richard D
Subject: Re: [TN] qualifying a heatsink attach process
Graham,
look like it is two step process: (1) mounting heat sink to your
parts (2) mounting parts to PWB - X-ray might be able to inspect with
step (1) effectively, but if you do the X-ray after assembly, it
would be difficult - assume you use high power transistor, you have
high power layout board with heavy metal layers. The transistor/heat
sink is relatively easy to inspect by X-ray (semi basically is
transparent, you can see the voids at heat sink easily). If you want
to inspect at assembly level, you better have 3D X-ray and do the
slice (even that the signal might not be that good if your board got
heavy metal layout). preform at parts level is great - after reflow,
you don't need to worry too much at assembly level for 2nd melt (not
much flux)... but do it after the PWB process, silver epoxy (liquid)
is much better with a proper weight. IMHO.
Look like your customer did heat sink attachment as after thought -
fix a immature design... just be careful (of course, designer is
always right as long as they don't need to build it in masses).
good luck.
jk
On Aug 30, 2018, at 2:33 PM, Stadem, Richard D wrote:
There are many labs that offer X-ray or CT scans, along with
microsectioning, etc. For a one-time or for occasional requirements
they are great.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Graham Collins
Sent: Thursday, August 30, 2018 1:26 PM
To: [log in to unmask]<mailto:[log in to unmask]>
Subject: [TN] qualifying a heatsink attach process
Hi technet!
We've got a customer working with high power transistors, they want to
use solder pre-forms to solder a heatsink on top of a row of
transistors. So the stackup will be PCB - transistor - preform -
heatsink, where the heatsink will span a row of 5 transistors.
The question is how do we establish that this is working OK and isn't
full of voids? This is at the "ok, we think this will work but we
need
to qualify the attachment method" stage. I've come up with a
couple of
options:
1) tear / grind it off and look for anomalies - not very sure to find
issues.
2) x-ray it - we don't have a 3-d x-ray so I'm not confident in our
abilities to find voiding. We do have a nice static x-ray though and
will try it to see how well it can see.
3) Sonoscan it to look for voids? Would have to be outsourced.
Am I missing any obvious options?
--
Graham Collins
Senior Process Engineer
Sunsel Systems
(902) 444-7867
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