[Diy_efi] Re: Diy_efi Digest, Vol 25, Issue 8

[Bill Washington]

Steven,
    As usual there are pros and cons both ways -
 the LQFP package would be the most straight-forward to use, and though 
the lead pitch is fine it can be hand soldered - but carefully with a 
very small tip and good flux - for hand soldering SMT parts a small 
small bottle of low residue liquid flux, or a syringe of paste flux is a 
great help.
the cons of this package are that it cannot dissipate heat as readily 
(heat dissipation is mainly through the legs) and it occupies more board 
space.

the LFCSP package occupies much less board space and has much better 
heat dissipation through the metal slug in its base.
The cons of this package are:
It cannot be hand mounted or re-worked (the pads are under the chip) - 
it requires a reflow oven to load and specialised equipment to remove.
The metal slug in the base must be soldered to an earthed pad on the 
board, with ground plane on all layers and at least 9 vias (plated 
through holes about 25thou diameter) to allow the excess solder to wick 
through the board, and pull the chip down into close contact with the PCB.

In my job we use both package types as well as special quad flat packs 
with a thermal slug in the base.......

For your application I would suggest that the LQFP is probably the 
better option.

Regards
Bill
>>  
>>   
>
>
> ------------------------------------------------------------------------
>
> Subject:
> Re: [Diy_efi] Surface mount
> From:
> "Steven P. Donegan" <steve at donegan.org>
> Date:
> Mon, 12 Mar 2007 16:35:35 -0700
> To:
> diy_efi at diy-efi.org
>
> To:
> diy_efi at diy-efi.org
>
>
> Since I've never done any SMT work I at present have no real
> understanding of the pro's/con's of the packaging. Any ideas in this
> area I'd certainly like to hear.
>
> On Tue, 2007-03-13 at 10:08 +1100, Bill Washington wrote:
>   
>> Steven,
>>     Which package will you be designing for, the Lead Frame Chip Scale 
>> (LFCSP) or the Low Profile Quad Flat Pack (LQFP)?
>> Regards
>> Bill
>>
>>     
>