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]
> 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]>
> Date: 31 August 2018 at 3:22:52 AM SGT
> To: [log in to unmask] <[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]
>> 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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