Chris, why don't you reflow solder the parts under the shield and then wave solder the shield into the board?
Maybe you can make the shield sit into some plated through cut out's made to the board and just hold it with some holes?
That way you'll have both solder the components and the shield.
Leo Tovar
IPC CID #10037
Chris Murphy <[log in to unmask]> wrote:
>Dorothy,
>
>thanks for the info. The main reason for placing and reflowing these shields during the SMD
>process is one of cost - the shields are cheap and we can use standard P&P machines. We tried
>looking at things like shield clips, shields that were half etched in the tops so that you can
>peel off the tops, removeable lids, shields with a conductive injected material for inner
>walls. All proved to be prohibitively expensive - I'm not sure quite why - maybe there are
>patents on all these things pushing the price up.
>
>We also looked at using a chassis with segregated compartments but the RF guys didnt think
>that we could get good shielding this way.
>
>Have you had any experience with conductive adhesive? Presumably you use a dispensing robot
>in line with a P&P machine? How easy is it to rework the cans after the adhesive has set?
>
>Is there any calculation to work out the maximum hole size that a shield will allow for a
>certain frequency? This product range I think will operate between 66 and 900 MHz.
>
>Finally what do you think of IR rework for RF shields - just get the heat to the tops and let
>the shield conduct the heat down to the solder joint?
>
>Thanks again,
>
>Chris Murphy
>
>Jack Crawford wrote:
>
>> >>> <[log in to unmask]> 09/18/01 06:16PM >>>
>>
>> Chris,
>>
>> Have you thought of using shield clips or fences or conductive adhesive so
>> the shield cover can go on as a final mechanical process? If shield covers
>> were a final step then they would not be exposed to high temperatures or be
>> sucking heat from all the components under its domain and exposing the rest
>> to sometimes excessive heat. What frequency is this assembly going to
>> operate at? Can some of the shielding be in the box it is installed in
>> rather than on the PCB itself?
>>
>> As for rework, a nozzle can be made for every shield shape that is
>> nonstandard and there are many rework stations that could then remelt or
>> remove/replace a shield. Of course you could always get a laser if you got a
>> lot of extra money in your back pocket.
>>
>> Dorothy Lush
>>
>> > ----------
>> > From: Jack Crawford[SMTP:[log in to unmask]]
>> > Reply To: TechNet E-Mail Forum.
>> > Sent: Tuesday, September 18, 2001 9:49 AM
>> > To: [log in to unmask]
>> > Subject: Re: Rework of RF shields
>> >
>> > >>> Chris Murphy <[log in to unmask]> 09/17/01 11:11PM >>>
>> >
>> > Hi Technetters,
>> >
>> > I have got a board covered with SMD RF shields in front of me, ranging
>> > in size from 15mm x 15mm to 140mm x 40mm to 70mm square. The spacing
>> > between them is only 1.5mm, and they are up to 12.5mm high.
>> >
>> > I am working through the many issues with these, such as methods of P&P,
>> > board / shield warpage, and how we are going to reflow parts under
>> > them. My question is does anyone know of equipment out there that we
>> > can use to rework these shields? I vaguely recollect seeing a machine
>> > that moved a hot air nozzle rapidly around in a rectangular pattern, but
>> > I am not sure how effective it will be for larger shields that are
>> > spaced so closely together.
>> >
>> > Is there anyone else doing this type of board, and does anyone have any
>> > supplier contacts?
>> >
>> > Any replies greatly appreciated.
>> >
>> > Thanks,
>> >
>> > Chris Murphy,
>> > Production Engineering,
>> > Tait Electronics,
>> > Christchurch,
>> > New Zealand
>> >
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