RAL Instrumentation Department Viraj Perera

Generic Test Module & BGAs

• Similar architecture to DSS with Virtex FPGAs

RAL Instrumentation Department Viraj Perera

Generic Test Module

• For ATLAS and CMS to test algorithms

• Delivered in December 2000– Incorrect device supplied and fitted

(XCV600 instead of XCV600E)– Component distributors took

responsibility for the mistake– Re-worked twice without successes

• This took long time December 2000 to April 2001

– However one board was usable with some bits missing

• CMS is using it now to develop their firmware

– Ordered two new boards and components• PCBs arrived on time (26/5/2001)• Waiting for the XCV1600E from Insight• Should be available for use by June/July

2001

RAL Instrumentation Department Viraj Perera

BGA Re-work

• Still investigating re-workability of BGAs– another company found with different re-work

machine (infrared - see below)– Replaced fine pitch (0.5mm) TQFP (304 and

208 pin) devices successfully on a DSS previously thought not possible with a hot air tool

• Damage to pads, components around it coming off, etc

– To gain experience, shall try the GTM with this method if there is no damage to the module after the previous two attempts

RAL Instrumentation Department Viraj Perera

ERSASCOPE

• Visual inspection after:– Assembly– Re-work

Optical Instrument

RAL Instrumentation Department Viraj Perera

ERSASCOPE Visual Inspection -Typical BGA Problems Uncovered

• Database with typical problems and solutions

immediately available to the operator

RAL Instrumentation Department Viraj Perera

Problems with BGA assembly on 9U modules!

• The manufactures do not see any problems assembling BGAs (fine pitch (1 mm) or ‘standard’ (1.27 mm)) onto a 9U module.– Discussed the CPM

• ~30 BGA packages + – ~ 20 Fine pitch BGAs

– Few things to consider:• PCB design (ground planes etc) to

prevent bowing at re-flow• PCB surface finish• BGA outline (alignment markings)

– Usually done with silk screen• Tolerance from board-to-board may

differ

– Prefer corners marked with copper• Avoid components (ICs) on back of the

module

RAL Instrumentation Department Viraj Perera

Problems with BGA assembly on 9U modules!

• Message:– With complex modules, over-the-

wall approach could cause problems!

• Designers, PCB manufacturer and board assembler must work together and understand requirements for each stage!