BARE DIE: HANDLING AND STORAGE - Power …

1 AN-1060 International Rectifier 233 Kansas Street, El Segundo, CA 90245 USA! bare die : HANDLING AND STORAGEBy Richard ClarkIntroductionInternational Rectifier supply a range of powerdevices in a variety of packages and in Bare Dieform. The bare die products are available in avariety of formats from whole wafers to of these products, whether packaged orunpackaged, require best STORAGE and handlingpractices to be purpose of this guidance note is to lookspecifically at the HANDLING and STORAGE of BareDie products. A few precautions in the STORAGE , HANDLING , die mounting and wire bonding shouldhelp to minimise product introduction time andminimise production International Rectifier bare die productsare unpassivated.

2 These products may be moresusceptible to HANDLING damage on the top sur-face of the die. The pick-up tools and collets usedby automatic HANDLING equipment may need tobe optimised in terms of design (shape) andmaterials of that: it is not the intension of thisdocument to specify or recommend ; it isonly a means of presenting some basicguidance. However, where a statement hasbeen extracted from an IR document orInternational Standard it will be appropriatelyidentified and Carrier TypeBare Die are available in several formats toaccommodate the customer s prototype orproduction requirements.

3 These include: Whole wafer Sawn wafer on film and frame, ChipPak or Waffle pack individual diepicked from sawn wafer and placed intowaffle tray. Pocket tape, tape and Reel individualdie on continuous feed containers and carriers for bare die productsare labelled and sealed to protect the die fromdamage or contamination. It is important thatthese seals are only broken when the packageis in a suitable clean environment, such as alamellar flow station of FS 209 Class 1000 (ISO14644 Class 6) or better. All receipt and inspectionoperations must be performed under clean con-ditions optimised for HANDLING bare die bare die products sold on film or tape willhave a limited shelf life due to the deteriorationof the adhesive used on the film/ tape, typi-cally the adhesion strength increases in products are built to order in order tominimise the risk to the customer.

4 Therefore, itis recommended that these products are pur-chased, stored and used in a controlled mannerwithin three months, to prevent loss of yield that this is a property of the adhesiveand not the wafer or Die products need to be stored in a tem-perature, humidity and contamination controlledenvironment. The optimum STORAGE conditionsfor bare die products are: Particle count: Class 1000 or better. Temperature: 65 F to 75 F (18 C to24 C) Humidity: <30% Nitrogen: Dryness < 4 ppm ~ -114 C above STORAGE conditions were extractedfrom JEDEC Standard JESD 49 ProcurementStandard for Known Good Die .All die products should be stored in this environ-ment when not in use.

5 This includes the as re-ceived product still in its sealed packaging andpartly used work in progress product. It may,however, be wise to separate the as received stock from work in progress to avoid any po-tential for cross contamination and to minimisethe disruption of the controlled environment inthe work in progress compartment or Die products that are stored for longer pe-riods of time than recommended by the due date or warranty period should be inspected on a rou-tine basis to verify the condition of the die to lookfor signs of contamination, oxidation or corro-sion. bare die on film or tape should also bechecked for ease of and TransferBare Die products are electronic componentsand as such should be regarded as static sensi-tive, in the same as any other electronic compo-nent.

6 Full ESD precautions should be followedduring all Die products should be handled with greatcare at all times and should remain secure intheir carriers except during unloading or inspec-tion operations at dedicated workstations. Ex-posure of wafers or bare die to the general work-ing environment, even in a cleanroom, can re-sults in contamination or die in a ChipPak tray or waffle packwill not rotate or flip provided that the paper andlid are in place. Without the lid, the slightest dis-turbance could cause mis-orientation of low volume and engineering runs it may notbe cost effective to use specialised automateddie HANDLING equipment.

7 In these situationsmanual HANDLING may be is imperative in these situations that twee-zers, of any form, are not used to pick up,transfer or place bare die . Tweezers oftencause mechanical damage to the die, the top surface in the form of scratches, or tothe bulk silicon in the form of chip-outs, micro-cracks and damage is sometimes visible during sub-sequent inspection but often does not manifestuntil electrical testing. For example, a scratchcausing a bridge between metal tracks may bevisible at inspection and if tested should causea short. But, a crack in the bulk silicon may ef-fectively introduce an area of insulation that maymanifest itself as high RDSon failure at the damage may be latent, present-ing a reliability these reasons it is recommended that anymanual die HANDLING operation use suitably de-signed tools such as vacuum pencils with care-fully selected tips for sawn-edge pick-up.

8 Thereare a number of suppliers of such recommended supplier is Research InstrumentsLimited ( ).Where automated die pick and place equipmentis used a soft silicon/ rubber tip or 4-sided in-verted pyramid collet of suitable size should beused. This is particularly important forunpassivated die where mechanical damagemay occur causing device failure. Routine in-spection and cleaning of the tips or collets is rec-ommended to avoid die to die contamination ormechanical damage. The pick and place pres-sure should also be minimised to prevent physi-cal damage that may cause failure or perfor-mance degradationMounting (Die Attach)International Rectifier wafers, and hence die, arecoated with metal on the back side.

9 Details ofthe metallization scheme are shown on the BareDie product datasheet. The purpose of the backmetallization is to provide a good thermal andelectrical interface between the die and die at-tach material. The back-metal is also solderable,therefore providing customers with the widestpossible choice of die attach options from con-ductive epoxies to specialised lead-free final choice of die attach or solder materialwill depend on the performance requirements ofthe device. All bare die product datasheets showdevice performance based on the die assembledin a specific package. The die attach commonlyused for this assembly is a lead-free die attach material is used it is im-portant that the die are placed with sufficient pre-cision to produce a uniform, void free, secureattachment.

10 For solder die attachment thereshould be minimal fillet on all sides and must notencroach onto the top surface. For epoxy dieattach there should be a fillet of at least 50% ofsidewall height on at least three side of the die,but no encroachment to the top presence of voids in the die attach or soldermay restrict thermal and electrical flow betweenthe die and circuit board. This may result in ageneral performance degradation or catastrophicfailure where localised hot spots occur at the voidresulting in thermal BondingInternational Rectifier cannot recommend bondwire selection or bonding conditions to custom-ers of bare die products.