Hi Lee,
I totally agree with the the first point you make.
We bake flex boards at 130?C for 3 hours.
Then the boards should be reflowed within 6 hours or else be stored in a
conditioned environment (< 20% RH) when the batch is too large to handle
within 6 hours.
For the second remark you make ,I also prefer Full Convection reflowovens.
Once we had an experiment ,where we compared two reflow ovens.
The profiles ( not to be mistaken with the settings) were the same , but in
one of the ovens we didn't use convection .
There was no delamination observed on the pcb that ran through the full
convection oven.
But the pcb from the reflow oven with no convection , showed some
delamination.
So its my opinion that it is not quit possible to get the same results from
a IR oven.
Perhaps this wil shed some new light on the oven issue,
Jowan Iven
Process Engineer Manufacturing
Stork Electronics
-----Original Message-----
From: Lee Whiteman [SMTP:[log in to unmask]]
Sent: Friday, September 08, 2000 2:37 PM
To: [log in to unmask]
Subject: Re: [TN] Flex PCB's
<< File: ATT00001.htm >> Mick Thwaite,
1. PCB's should be baked out prior to use. Depending upon the PCB's
material
(FR4 vs.. polyimide), the board should be baked out at over 100C for
between
1 - 4 hours. I've seen instances where people have baked out boards up to
24
hours before use, but I believe 1 - 4 hours is sufficient.
2. Hot Air Convection vs.. IR Reflow. I would be more concerned with how
well you control the reflow soldering process versus the type of reflow
soldering process used. Hot Air Convection does provides better heat
transfer than IR Reflow. However, I've done IR Reflow soldering with
positive results on boards with SMT devices. I would recommend Hot Air
Convection over IR Reflow, but if you currently have an IR Reflow oven, and
you can't buy a new Hot Air Convection oven, with care you can get the same
results with IR Reflow as with Hot Air Convection.
3. Too long ago, I used an anodized aluminum vacuum fixture to hold down
parts for wire bonding, and it worked well. The deal was to design it
taking
into account the tolerances of the device.
I hope these answers help you and that I did not strike out with these
answers.
Good Luck
Lee Whiteman
Senior Manufacturing Engineer
ACI / EMPF
Telephone: (610) 362-1200; Ext. 208
FAX: (610) 362-1290
E-Mail: [log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Mick Thwaite
Sent: Friday, September 08, 2000 4:02 AM
To: [log in to unmask]
Subject: [TN] Flex PCB's
We are just starting to use flex PCB's in our production area.
Is it true that the PCBs have to be dried prior to using as they absorb
moisture quickly?
Is it also true that hot air is better than IR reflow?, and
Does anybody have any good ideas on the materials to use for the vacuum
jig to hold down the panel during wire bonding?
We have used vacuum holds as small as 1.00 mm but still find that the
PCB moves during bonding.....
Mick Thwaite
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