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January 2011

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From:
Mike Fenner <[log in to unmask]>
Reply To:
Date:
Fri, 14 Jan 2011 16:13:25 +0000
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I have!

Regards
 
 
Mike

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: Friday, January 14, 2011 1:53 PM
To: [log in to unmask]
Subject: Re: [TN] Trace Widths Entering SMT

Hi Mike,
The shape of the reflow profile, mostly ramp-soak-spike, comes from the heat
transfer needs to minimize T-differences at the spike and peak regions.—and
things certainly have gotten worse with Pb-free.
The flux chemistries can be adjusted to these heat-up shapes. To make
consistent good quality solder joints it is the peak reflow T that is most
important, but it is also this peak T that causes the damage in PCBs and
components.
VPR machines have come a long way since early machines gave VPR a bad
name—you really need to take a look at these machines with controlled
programmed vapor fluid injections and other operating features. The machines
from the 3 main VPR machine suppliers (Rehm, IBL, Asscon) are quite amazing
and very capable. 
And they make it possible to properly solder even very large BGAs with SAC
solders at very much lower T's than is possible with multi-zones.
So, I stand by my statement.
Werner


 

 


 

 

-----Original Message-----
From: Mike Fenner <[log in to unmask]>
To: 'TechNet E-Mail Forum' <[log in to unmask]>; 'Werner Engelmaier'
<[log in to unmask]>
Sent: Fri, Jan 14, 2011 5:36 am
Subject: RE: [TN] Trace Widths Entering SMT


Morning Werner

HNY



May I respectfully question your statement below?



I am a big fan of VPR/Condensation reflow and was instrumental/involved in

its European debut installing the first machines and working with 3m HTC

etc. but even I would not have been quite as unequivocal as you below.



The reduced delta T at peak and inherent temperature limitation are

advantageous and stem from the equilibrium nature of the heating process.

The load independent nature of the process is also important.



However IMHO the real key to successful reflow is controlling the profile

shape rather than peak. VPR is poor in this respect, compared to convection

ovens. 



VPR is not the only equilibrium process, some of the more efficient

Convection machines can also run in equilibrium (easily demonstrated by

leaving a thermocouple from profiler free floating) and being multi-chamber

are much easier to profile than a single chamber VPR machine. 

The natural ramp rate of a saturated VPR process is about 50C/second and

trying to control this to <4C is difficult and compromises some of the VPR

attributes. 



I am trying to setup a small investigation on VPR here in UK with the object

of writing an article or possibly a paper and hopefully will have some more

light to shed.



Meanwhile I would appreciate your comments.



Regards

 

 

Mike

ü Please consider the environment before printing this e-mail

-----Original Message-----

From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier

Sent: Wednesday, January 12, 2011 8:08 PM

To: [log in to unmask]

Subject: Re: [TN] Trace Widths Entering SMT



 Vapor phase is better than any other heating method for two reasons: (1) no

over-temperature possible, (2) more uniform heating.

Werner



 





 



 



-----Original Message-----

From: Ioan Tempea <[log in to unmask]>

To: [log in to unmask]

Sent: Wed, Jan 12, 2011 10:54 am

Subject: Re: [TN] Trace Widths Entering SMT





No do Carl,







IR or convection do not bring everything at temperature at the same time.

Don't 



know about vapour phase though.







Imbalance is an important cause for tombstoning.







Regards,







Ioan Tempea, ing.



Ingénieur Principal de Fabrication / Senior Manufacturing Engineer



T | 450.967.7100 ext.244



E | [log in to unmask] 



W | www.digico.cc







N'imprimer que si nécessaire - Print only if you must











-----Message d'origine-----



De : Carl VanWormer [mailto:[log in to unmask]] 



Envoyé : January-12-11 10:50 AM



À : [log in to unmask]



Objet : Re: [TN] Trace Widths Entering SMT







Novice question . . .



I was told that the heating imbalance "goes away" in the IR reflow



process, since "the whole thing" has been brought up to temperature at



"the same time".  







Question:  can we "mostly ignore" potential thermal imbalances caused by



asymmetrical traces shape/width for IR reflow process boards?  (or have



I been lied to, again . . .)







Thanks,



Carl







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