Importance of Exposed Pad In ST QFP for Set top box product Views: 917

Importance of Exposed Pad In ST QFP for Set top box product				rajeshwara	09/27/09
Importance of Exposed Pad In ST QFP for Set top box product				davef	09/28/09
	Importance of Exposed Pad In ST QFP for Set top box product			rajeshwara	10/01/09
		Importance of Exposed Pad In ST QFP for Set top box product		davef	10/01/09
			Importance of Exposed Pad In ST QFP for Set top box product	rajeshwara	10/30/09

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Date: September 27, 2009 11:41 AM
Author: rajeshwara  
Subject: Importance of Exposed Pad In ST QFP for Set top box product

We are using ST Demodulator QFP in our product which have exposed pad / heatsink from bottom side. Visually or in magnifier the solder joint or fillet looks good but if we touch up the pins with soldering guns , PCB works fine.

(http://www.smtnet.com/distributed_forums/Index.cfm?CFApp=8&Message_ID=59990)

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Date: September 28, 2009 04:15 PM
Author: davef  
Subject: Importance of Exposed Pad In ST QFP for Set top box product


That your solder connections reflow properly when heated with a soldering iron, indicates that that your reflow recipe needs improvement.
* Thermocouple the pads that require touch-up and adjust your oven recipe to assure that they reach liquidous+20*C for 5 to 10 seconds
* Use IPC-7530 Guidelines for Temperature Profiling for Mass Soldering (Reflow & Wave) Processes

We are uncertain about what you're asking us about an "exposed pad."

(http://www.smtnet.com/distributed_forums/Index.cfm?CFApp=8&Message_ID=60007)

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Date: October 01, 2009 06:22 AM
Author: rajeshwara  
Subject: Importance of Exposed Pad In ST QFP for Set top box product


We approved the Reflow Profile from Cookson Solder Paste Manufacturer we are using. Now I am suspecting on method of vias designing below that QFP.There is exposed pad for that QFP and we print solder paste there , but when i see under x-ray there is creation of voids in between QFP and Exposed pad.

(http://www.smtnet.com/distributed_forums/Index.cfm?CFApp=8&Message_ID=60027)

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Date: October 01, 2009 08:34 AM
Author: davef  
Subject: Importance of Exposed Pad In ST QFP for Set top box product


First, the reflow thermal recipe provided by your paste supplier is only a ball park guess. Beyond that, the temperature measured by thermocouples on your oven heaters are only loosely related the temperature of solder paste on your board. You need to measure the actual temperature at the component lead.

Second, voiding between the exposed pad and the thermal sink on the board is not good.
* Is the proper amount of solder applied?
* Are vias filling with solder and reducing the amount required between the board and the thermal pad?
* Is solder draining through the via to the floor?
* Are the via plugged or capped?

Finally, search the fine SMTnet Archives for more on:
* Exposed pad
* Thermal pad
* Via* void*.

(http://www.smtnet.com/distributed_forums/Index.cfm?CFApp=8&Message_ID=60031)

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Date: October 30, 2009 08:24 AM
Author: rajeshwara  
Subject: Importance of Exposed Pad In ST QFP for Set top box product


thnx davef & all
With the help of all at last i solved the problem ,
The vias are not caped from bottom , so solder paste draining through the via to the floor which creates voids between IC ground pad and e-pad.

Tnhx all again

(http://www.smtnet.com/distributed_forums/Index.cfm?CFApp=8&Message_ID=60233)