be careful wave solder caps - thermal shock sometimes will result
hair line cracking of cap (ceramic) body... hard to detect by visual
and open/short test not going to fail either... but performance is
not good (usually you get field failure after some time...crack
propagation to critical length that impact performance)... just a
reminder.. Better method is wave 1st and populate the cap after
(your designer should know that at preliminary review stage - so you
have time to change build sequence by design consideration).
jk
On Mar 12, 2018, at 11:13 PM, Wayne Thayer wrote:
> Hi Carl-
>
> That's how SMT started! You don't want the caps on the bottom to be
> smaller
> than 0603. Larger is preferred, but those will work. You put the
> parts down
> in "SMT Adhesive", which is a high temperature low modulus
> material. This
> holds the part in place while it goes through the wave. You want to be
> careful about any parts going longitudinally through the wave
> because of
> the large thermal transient during travel--design the caps so both
> ends hit
> the wave at the same time, and you want to go through the wave
> relatively
> slowly.
>
> But even without that---Why solder 200+ pins instead of wave solder
> the
> pins and place the caps manually? For that method you would deposit
> the
> paste with a syringe and place the caps in the paste, then send
> through
> reflow with the connectors on there. If the connectors can't take
> the heat,
> then the caps must be reflowed using hot air rework station.
>
> Wayne
>
> On Mon, Mar 12, 2018 at 2:22 PM, Carl Van Wormer
> <[log in to unmask]
>> wrote:
>
>> Our new version PC board has a few bottom-side mounted capacitors
>> that
>> were not on our previous design. Both designs are low-quantity
>> builds of
>> about 100 per year. Our assembly house says they can’t run the
>> board
>> through their solder wave because of these parts and is planning
>> to charge
>> a significant fee to hand-solder the 200+ pins for the connectors. I
>> thought there was some sort of mask that could be placed over the
>> bottom
>> side parts, like the pink stuff they add to avoid filling the
>> plated holes
>> for mounting screws. Are there any good methods that I should
>> research to
>> help them run our boards through the solder wave?
>>
>> Also, I tried to find the TechNet archive to search for answers,
>> but I was
>> unable to use the search function. Is there a help file on
>> searching the
>> TechNet archive?
>>
>> Thanks,
>> Carl
>>
>>
>>
>>
>> Carl B. Van Wormer, P.E., AE7GD
>> Senior Hardware Engineer
>> Cipher Engineering LLC
>> 21195 NW Evergreen Pkwy Ste 209
>> Hillsboro, OR 97124-7167
>> 503-617-7447x303
>> [log in to unmask]<mailto:[log in to unmask]>
>> http://cipherengineering.com<http://cipherengineering.com/>
>>
>> This message may contain confidential and/or proprietary
>> information, and
>> is intended for the person/entity to whom it was originally
>> addressed. Any
>> use by others is strictly prohibited. If I sent this to you by
>> mistake,
>> please be nice and delete it, and then tell me of my mistake so I
>> can send
>> it to the right person.
>>
>>
>>
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