No problem, can be controlled with the Hakko. Do you control your cooldown every time your operator performs solder touchup with a soldering iron? How?
That's the difference!
-----Original Message-----
From: Joyce Koo [mailto:[log in to unmask]]
Sent: Friday, April 08, 2011 11:55 AM
To: 'TechNet E-Mail Forum'; Stadem, Richard D.
Subject: RE: [TN] Cracked ceramic capacitors
Cooling more than 60C/min? un-controlled?
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Friday, April 08, 2011 12:34 PM
To: [log in to unmask]
Subject: Re: [TN] Cracked ceramic capacitors
No, I have not tested them all. I am not that old.
The Hakko preheater is actually about the safest method of pre-heating I can find. Consider:
It uses a control thermocouple and monitors the board temp. This TC is attached to the bottom of the CCA, and should be positioned AWAY from the area being reworked. You set the target board temp so you keep the PWB safely below the Tg as listed in IPC 4101C slash sheet for the assembly you need to rework. You also consider the safe temperature range of the other components on the CCA. The reason you place the TC AWAY from the rework area is so that when you bring in the hot air wand, the TC does not sense the hot air wand heat and does not prematurely "think" the board has reached the desired set temp. The idea is to keep the WHOLE BOARD preheated to prevent the temperature gradients that lead to stresses from differing CTEs in different areas of the board. Those gradients are the cause of delamination, z-axis expansion, etc. The Hakko pre-heater has four quadrants that can be individually shut off or on so the entire board can be pre-heated evenly through the entire rework process. When the board temperature approaches the set temperature (target temp) it automatically goes into idle mode, and "flickers" the IR energy just enough to keep the board right at the target temp. It cannot run away thermally and damage the board, and it also automatically shuts off after a pre-determined time, but is easily restarted with the push of a single button to continue if needed.
The pre-heater IR energy is extremely efficient in heating the entire board. We use it here at GD and other of my client companies even on CCAs with metal heatsinks covering the entire board, and it is easily able to preheat even very massive boards safely. Other pre-heaters tend to focus the heat on a relatively small portion of the board, and when you do that and then come in with the hot air wand on top an operator can easily damage the board because so much heat is focused on a very small area of the board that is rapidly expanding, but the rest of the board is cold and is not expanding at the same rate, if at all. Again, the higher that gradient is, the more stress is applied to the board, and the easier it is to damage the board.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ioan Tempea
Sent: Friday, April 08, 2011 11:06 AM
To: [log in to unmask]
Subject: Re: [TN] Cracked ceramic capacitors
Hi Richard,
How would the Hakko preheater fare against the Zephyrtronics airbath, see http://www.zeph.com/mega_grid.html , as I am sure you have tested them all?
As a downside regarding the Hakko preheater I see the IR, requiring the operators to be more on their toes, in order to avoid burning the PCB. On the other hand, the Airbath is double the price, for a much smaller active area.
Thanks,
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 : Stadem, Richard D. [mailto:[log in to unmask]]
Envoyé : April-08-11 11:24 AM
À : [log in to unmask]
Objet : Re: [TN] Cracked ceramic capacitors
Option 1 will probably not flush out anything, and may cause other issues, very high risk versus little return.
Option 2 poses good probability of finding at least 90% of cracked caps with a good inspector and a good 30x microscope, and poses very little risk IF THE CORRECT REWORK METHOD IS USED.
Option 3 depends on the fallout percentage from Option 2. If you visually screen 10 boards and find a single cracked cap amongst those 500 caps (50 caps x 10 boards = 500 caps screened) then Option 3 would not appear to be a good choice. Option 3 would then represent unnecessary rework, with little return versus very high risk.
Use a Hakko FR1012B bottom preheater and a Hakko FR802 hot air wand to perform any rework :
http://www.hakkousa.com/detail.asp?CID=51&PID=2414&Page=1
http://www.hakkousa.com/detail.asp?CID=51,261&PID=4754&Page=1
You may not need the pre-heater, but you want to avoid large temperature gradients across the board. That is where the pre-heater helps.
I'll think of you when I am up north fishing this weekend. Have fun!
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Rivera, Raye
Sent: Friday, April 08, 2011 9:55 AM
To: [log in to unmask]
Subject: [TN] Cracked ceramic capacitors
Hello Technetters,
We had an issue with cracked SMT ceramic capacitors causing boards to fail functional test. We isolated the problem to a reel of parts that contained some cracked caps and purged these. Problem solved.
My question is about what to do with boards built with these capacitors before we purged. The boards pass functional test. The concern is that a cracked cap was loaded, but has not yet failed. The range of actions proposed here are:
- Temperature cycle the boards between -5 C and 55 C a few times. The theory is that this will flush out any latent defects.
- Visually inspect for defects.
- Manually change out all the suspect caps, about 50 per board.
Does anyone have thoughts on what would be the best method or another idea? We don't have ICT capability.
Thanks!
Raye Rivera
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