Concept Design for Daughter Cards

After dealing with poor fabrication yields for castellated daughter cards I tried to design a better mouse trap.

The biggest problem with castellated boards is router damage to via barrels as shown below.



Source:  Same Old Dog, Same Old Tricks, New Toys - Circuit Talk:

You need to qualify your fabricator very carefully for castellated boards. Be sure they have the experience and expertise to do the job right.  Many of the low cost off shore fabricators are still struggling with castellated board designs.

Concept Daughter Card

Shown below is a Concept Daughter Card.  I designed this solution to solve the router damage problem.

Note the use of the soldermask dams on the host PCB land pattern. The soldermask dams are intended control solder flow during standard SMD reflow process.

The Host Land Pattern Pads have also been extended beyond the body of the daughter card to permit hand soldering techniques to attach the daughter card. 

Solder can be feed through the VIA from the top side of the daughter card while holding a soldering iron on one of the extended pads of the host board.

Tinning the pads on daughter card and the host with solder is highly recommended for hand soldering.

Below is screen shot of a GPS Interposer board which I designed to adapt a newer GPS module to replace an obsolete GPS module.

A nice feature of this concept daughter card design is the ability to inspect the SMD reflow solder joints by looking in the VIAs. 

So what's the catch, where is the gotcha ?

If you need to remove the daughter card it will not be possible to draw the solder under the module back across the soldermask dam using a soldering iron and wick.

To remove the module you will need to apply rework techniques similar to those used to remove and replace BGAs using a hot air rework station.


Feedback and Comments are Welcome.

Best regards
Randy Clemmons CID+

Castellations - Printed Circuit Boards

Fabrication:

ST MICRO BLUE TOOTH MODULE SPBT2632C1A.AT2 

 ST MICRO BLUE TOOTH MODULE SPBT2632C2A.AT2 

ANTENOVA GPS MODULE, M10382-A1 UB  (not castellated, this is a LGA style mounted module)

"Recommendations and comments

When castellated features are required, it is best to use the following general rules when at all possible:

• Use the largest hole size possible
• Use the largest Outerlayer pad possible, both top and bottom sides
• If possible, place Innerlayer pads to anchor the hole barrel. This will also help reduce burring during the castellation process.
• If the castellation is not used for a mechanical connection (i.e. insertion of a connector device), allow additional dimensional tolerance for the castellation opening if possible."

Source: http://www.hitech.com.mk/en/technology/castell

Related Article:
Same Old Dog, Same Old Tricks, New Toys - Circuit Talk:

Soldering:

Soldering of Castellated terminations are mentioned in IPC-D-610 Section 8.2.4.

Thank you Bill Brooks for sharing the link to the old dog . . .


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