When I see the Pem's and overheated boards I wonder what profile was used.
SMT PEM's can be a challenge. The manufacturer has performance data posted 
on their website that gives the pushout and torqueout specs. These tables 
were developed using profiles that peaked at 258°C for SnPb and 270°C for 
SAC305 reflow. Since all boards have parts that can not handle this 
extreme, do your own testing and you can achieve close to the published 
specs with a more reasonable profile. You will need to apply some 
additional heat in your profile. We found the solder joints could fail 
with 2 inlb of torque if soldered with settings that everyone considers a 
standard reflow profile peak and preheat.


Roger Mack  P.Eng. 
Manufacturing Specialist
Parker Hannifin Electronic Controls
Electronic Controls Division
1305 Clarence Avenue
Winnipeg, MB  R3T 1T4 Canada 
direct 204 453 3339 x373
[log in to unmask]
www.parker.com/ecd







Steve Gregory <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
07-29-2010 20:34
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Steve Gregory <[log in to unmask]>


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Subject
Re: [TN] PCB Discoloration






Hi Linda!

While discoloration in itself is not a defect, I would be a little worried 
about these seven boards. Especially since the rest of the lot are not 
discolored like this: 


 http://stevezeva.homestead.com/PCB_Discoloration1.jpg

 

I don't see any delamination in the photos, but it sure looks like the 
boards got pretty toasty. I wonder if it was because the boards were 
sitting over a preheater or hot plate too long. From the looks of the 
components on the board, most of it was probably hand soldered (those PTH 
caps converted to SMT couldn't have taken reflow), and I imagine that the 
solid plane on on the backside of the board was a real heatsink. 
Preheating the board would have helped with soldering the PEM nuts for 
sure, but maybe the preheater was set too high. I know a Hakko IR 
preheater can smoke a board if you're not careful (not that I've ever done 
that, but I know a friend of a friend who did. Hehehehe).

 

Anyways, those seven boards saw more heat than the rest of them did based 
on the appearance in the photos. I don't think I'd buy off on them...

 

Steve

 

 

 

From: Linda Langley [mailto:[log in to unmask]] 
Sent: Thursday, July 29, 2010 1:42 PM
To: Steve Gregory
Subject: FW: PCB Discoloration

 

Hi Steve,

 

Here I go again asking for help from my experts! Can you please post these 
pictures? So I don’t have to bother the whole forum, would you know the 
name of the board guru that could answer my questions?

 

I am not sure if the discoloration is a defect, is this a form of 
delaminating? Why would only seven boards turn this color? They are all 
from the same lot.

 

Any information will be greatly appreciated.

 


Linda Langley CIT

Training Specialist

Jabil Circuit

248-292-6176

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