Lpc2000

Leon Heller wrote:

>----- Original Message ----- 
>From: "Ake Hedman, eurosource" <akhe@...>
>To: <lpc2000@yahoogroups.com>
>Sent: Monday, January 02, 2006 4:48 PM
>Subject: Re: [lpc2000] Soldering LPC2148
>
>
>  
>
>>Tom Walsh wrote:
>>
>>    
>>
>>>Ake Hedman, eurosource wrote:
>>>
>>>      
>>>
>>>>I have been looking for a source for syringes for solder paste. Where do
>>>>people buy theese?
>>>>
>>>>
>>>>
>>>>        
>>>>
>>>I also use these:
>>>
>>>http://www.zeph.com/pencil.html
>>>http://www.zeph.com/zephpaste.htm
>>>http://www.zeph.com/zt5_dir.htm
>>>
>>>It is nice to use the pnuematic paste applicator, it is great for
>>>rework.  Your hands can get very tired (not fooling you), trying to
>>>force that paste out a tiny needle!
>>>
>>>For building the board, a paste stencil + toaster oven is definately the
>>>way to go!
>>>
>>>
>>>TomW
>>>
>>>
>>>-- 
>>>      
>>>
>>Tom thanks!
>>
>>A dispenser would be good to have.
>>
>>I use a pre-heater today
>>(http://www.aoyue.de/en/Aoyue_853a_quarz_infrared_preheater_smd_rework_repair_desoldering.htm)
>>and it works fine for small cards following a temperature profile 
>>manually.
>>
>>An oven would be nice to have though for larger boards and smaller
>>series. I have tried to find one with a fan in Sweden but not found a
>>suitable one yet. Instead I am thinking about rebuilding one and putting
>>in quarts IR elements and control logic to get faster ramp up then it
>>has standard. As always time is my enemy... ;-)
>>    
>>
>
>The Jan 2006 issue of Elektor has a design for temperature controlled 
>toaster oven. I bought one before Xmas from Argos for just under 20 GBP, it 
>has two quartz elements on top and two underneath.
>
>  
>
Actually, I don't use any temperature control other than what is in the 
Oster oven.  I don't know if the dial is calibrated, but it works.  The 
oven does have the quartz elements, major reason that I purchased it, 
and I follow a:

1.5 minutes @ 125C (preheat)
1 minute @ 140C (staging)
1 minute @ 180C (reflow)

30 seconds into the 180C, the paste melts on the smaller parts and about 
10 seconds the larger parts' paste melts.  I hold the heat for that 
additional 10..20 seconds, then shut the oven off and crack open the 
door to spill the heat.  Over the next minute, I slowly and gently, 
fully open the door, slide the grille out to expose the PCB to ambient air.

After about 30 seconds in ambient, I use needle nose pliers to grasp the 
board and remove it.   Meanwhile, I have a "slab" of aluminum waiting, 
this is about 3/8" (100mm) thick, by 10" X 10" (25cm X 25cm).  I gently 
slide the PCB onto the aluminum plate to suck the heat from the PCB.

What I have found is that you can leave the board in the heat for too 
long.  I tried a preheat of 3.5 minutes and the resulting solder looked 
like there may have been some embrittlement (under microscope), the 
shorting the preheat time (to boil out water) results in shiny joints.

If you reference the article on Sparkfun, you'll note that they are 
using SOP devices, fairly large.  They are manually holding the stencil 
in place.  With a significantly sized TSSOP board, it is impossible to 
maintain alignment! What I do is to "pin" the board in place by 
surrounding it with like thickness PCB material.  Then carefully 
position the stencil and tape it down.

I've found that the stencil will shift when you attempt to remove your 
fingers from contact with it.  This problem is taken care of by some 
small codiment dishes (about 2" dia - 50mm).

I do use a Madel stainless steel squeegee: 
http://www.ntscope.com/Merchant2/merchant.mvc?Screen=PROD&Return_Screen=CTGY&Store_Code=MTC&Category_Code=TAM&Product_Code=SQG-15

That sqeegee is the only "high-tech" equipment used in the entire 
process.  :-)


Regards,

TomW



-- 
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
----------------------------------------------------